General Information / Basics
Checking Valve Timing
Found out how to check valve timing and/or timing chain stretch
WITHOUT removing the front cover today.
Remove the distributor cap, right valve cover and the #4 cyl rocker arms
and pedestal. turn engine to TDC on the #4 cyl (rotor pionting to #4 and
timing mark on balancer lined up with 0 on the pointer).
Set up a dial gauge on the #4 intake push rod.
Rotate the engine to TDC #1 cylinder.
- If the dial reads 185-190 thousands, your valve timing is right.
- If the dial reads 125-130 thousands, your valve timing is retarded or
your chain is streched.
- If the dial reads 250-255 thousands, your valve timing is to far advanced.
These #s are for stock engines and wouldn't work for engines
with aftermarket cams.
[ Thanks to Bob Blanchard
for this information. ]
Corona Effect
The Corona Effect is what causes neon signs to
work. By inducing high voltage in the tube, the gas is ionized
and thereby lights up. In the case of plug wires glowing, the
Corona effect can happen when atmospheric conditions are
right. High humidity and low barometric pressure combined
with the high voltage of the ignition system will create an
electrostatic field around the plug wires and will in effect,
ionize the ~air~ around the plug wires. Thereby causing the
glow. Since this is a breakdown of the surrounding air
(not the wires) it will not affect ignition performance.
That is of course assuming your plug wires have not been
ahem, chewed on by mice ;-)
Also, since wide plug gaps require a higher voltage to fire
them, this will increase the chances of the Corona Effect.
Usually more visible around the plug wires
rather than the plugs. Note: not to be confused with
the Corona "after effect" of excessive consumption of Coronas
with limes.
[ Thanks to Greg Rollin
for this information. ]
Determining Accuracy of Harmonic Balancer Mark
On my old Olds engines I've had plenty of trouble with the rubber
deteriating on the harmonic balancer. Then the outer ring starts
sliding around, and the timing mark is meaningless. Eventually one
came off and rested against the front timing cover
I check it by pulling the 1, 3, and 5 spark plugs. First bring piston
1 to the top, and the mark should be close to zero. This is not a very
accurate indicator of actual crank position since piston speed is
minimum here. So next I probe down 3 and 5, and adjust the crank so
these 2 pistons are exactly THE SAME distance down. Since these pistons
are at maximum speed (in opposite directions), this sets the crank more
accurately at zero degrees
Replacing a damper with another the same age is not a long term fix. Dick
Miller rebuilds these.
[ Thanks to Bruce Roe
for this information. ]
Distributor, Crank, Cam Relationships
The distributor must turn once to feed every cylinder a spark for every
complete cycle. A complete cycle is by definition 4 strokes, or two turns of
the crank. Therefore, dist'r speed = cam speed = 1/2 crank speed. And, turning
the dist'r by say 2° alters timing by *4* crank degrees.
For an engine turning 1000 RPM at the crank, the cam is turning 500 RPM, and
the distributor is also turning 500 RPM.
Given a
firing order of 18436572 then I'd say that #8's throw will be 90° behind,
or CCW of the #1 crankppin. #4 will be 180° CCW [not that that matters for
180...], etc. As viewed from the front of the engine.
[ Thanks to Chris Witt, Al Varhus
for this information. ]
Distributor Shaft Play
Careful with this tolerance. Up and down movement is normal, but unfortunately,
too much can cause problems. Since the distributor drive gears are
helically cut, up and down play in the distributor shaft can lead to
timing changes as the distributor driven gear moves up and down
relative to the cam gear. Mr. Gasket and others sell shim kits which
allow you to take out most of this unwanted motion. These are simply
precision ground washers of various thicknesses which go between the
distributor gear and the housing to take out the end play. Just drive
out the split pin holding the gear to the shaft, place the shims over
the end of the shaft, and reinstall the gear and retaining pin.
[ Thanks to Joe Padavano
for this information. ]
Ignition Advance
The reason for ignition advance
is that the air/fuel mix doesn't burn instantaneously - it takes a little bit
of time from the moment the spark is set off to the moment when peak cylinder
pressure is reached. During that time, the crankshaft keeps rotating. So if you
lit off the mix at TDC, the piston will be well down the bore by the time peak
cylinder pressure is reached, and you'll get lousy horsepower and lots of
unburned fuel out the tailpipe. The cure is to light off the air/fuel mix
*before* the piston reaches TDC, so that the peak cylinder pressure is achieved
at just about the time the piston is positioned to take full advantage of it.
This is what we call ignition advance.
Okay, let's back up a bit. Why do we need any ignition timing advance at
all? Why not light the fire off when the piston is at TDC? The answer is
that it takes the flame some time to grow to fill the whole combustion
chamber, and during the time the flame is growing, the piston keeps moving.
The only way to get the flame to finish burning and produce lots of
pressure on the piston when it's ready to be pushed down the bore, is to
light it off early, while the piston is still moving up the bore. That is
why ignition timing is needed.
How much advance do you need? Clearly, it depends on how fast the air/fuel mix
burns, and how fast your engine is turning. Roughly speaking, if your engine
is turning faster, you want more advance; this is the why distributors have
mechanical advance in them, which puts out the spark earlier and earlier in the
cycle as the engine rpm's climb. Once you reach a high enough rpm, the
air-fuel mixture begins to whoosh into the cylinder with so much velocity that
it becomes turbulent, and consequently the flame spreads very fast; increase the
rpm, and the mixture becomes more turbulent in direct proportion, and the
flame spreads even faster. This means that once you exceed a certain high
rpm, the mixture tends to burn in about the same number of crankshaft degrees,
no matter what the rpm. Now you no longer need the ignition timing to keep
advancing with increasing rpm, so the distributor is designed to level off the
advance above some rpm.
The somewhat large overall advance numbers seem too large to believe,
and it freaked me out also. However, when I began to understand the role
of ignition timing, I began to understand why this much timing is
okay in certain cases.
Your distributor contains a mechanism (mechanical/centrifigal advance)
of springs and weights that advances the spark timing as engine rpm goes up. This is
to compensate for the fact that the engine turns faster, so it goes through
more degrees of rotation in the time the flame spreads through the chamber.
To compensate the flame is lit off earlier.
The distributor also contains a vacuum advance canister. It's role is to add
a bit of advance during certain high vacuum phases of driving, like cruise,
mainly for fuel economy.
The reason for vacuum advance is that the rate at which the air/fuel mix burns
also depends on how much of it is packed into the cylinder in the first place -
i.e., how dense the mix is. When the engine is driving around at
part-throttle, the almost-closed carburetor throttle blades restrict the amount
of air/fuel mix entering the engine (compared to wide open throttle). This
low-density mixture burns more slowly. To compensate, the ignition needs to be
fired off earlier when the engine is at part throttle (than when it is at full
throttle). The clever solution is vacuum advance. When the engine is at part
throttle, manifold vacuum is high, and this sucks on the vacuum advance
diaphragm and advances the spark. If everything is set up correctly, the extra
advance compensates for the slower-burning mixture.
Vacuum advance during WOT acceleration is a common myth. More than one mechanic
has told me this one. Part throttle yes, but not all out acceleration.
When the engine is at part-throttle (cruising
at constant speed on level road, for instance), the intake manifold vacuum
is high and engine load is low. That is to say, the resulting air/fuel mix is lean.
And it turns out the speed at which a flame spreads in an air/fuel mix
decreases when the air/fuel mix is thin. So the flame takes longer to spread from
the spark-plug and fill the whole combustion chamber. If we want the
combustion process timed right, then, we need more ignition advance at
part throttle, to compensate for the slower flame burn in the leaner
air/fuel mix. And this is exactly what the vacuum advance does: the vacuum
cannister measures engine vacuum, which is to say, it measures engine load.
The lesser the engine load or need, the more the spark gets
advanced. Exactly what the engine wants, and a very clever idea!
During acceleration, there is less vacuum signal. Vacuum advance is less
when there is less vacuum, using either manifold or ported sources, as I explained above.
Most vacuum advance units are not adjustable - the factory figures out what
works to meet emissions requirements, then presets that amount in the
vacuum cannister design. Some Mopar units are adjustable from the factory.
For Fords and GM cars you can buy aftermarket adjustable vac. advance units
(Accel, Crane, etc).
VACUUM ADVANCE:
If you didn't disconnect the vacuum advance when setting the timing, it
is probably bumping up your advance as you hit third gear, since
your vacuum starts to come up as you approach top speed.
It dials in greater ignition advance, which is necessary when you've got a
thin or lean air-fuel mixture such as at part-throttle; you have to start that
mixture burning quite early in order to get all that fuel combusted by the
time the piston is passing TDC.
It greatly improves part-throttle fuel-economy. You can disable it
temporarily with a golf-tee plugging the line to the canister.
It also bumps your idle speed up. That's it. Makes little to no difference for
actual driving, only for idle emissions quality.
Bob Barry
The total amount of advance or overall advance depends on many things (compression ratio,
head design, rear-end ratio,
weight of your car, etc) but I've been told numbers of around 10° to 15°
advance at idle, around 36° full mechanical advance (with
the vacuum advance disconnected). At part throttle, high rpm, with vacuum
advance, the ignition timing should be somewhere in the range of 50°.
That number surprises many, but that's what's needed for maximum
fuel economy at part throttle (cruising).
Total advance at high rpm and wide open throttle = initial timing +
mechanical advance
Total advance at high rpm and part-throttle = initial timing + mechanical
advance + vacuum advance
One rule supercedes everything else: if the engine detonates, reduce the
timing immediately till all traces of detonation are gone. Detonation will
kill your engine in a very short time (it breaks piston rings, crumbles
pistons, etc.).
The best way to set ignition
timing is to modify the initial advance and advance curve to get the best power
at WOT at all rpms. Do this with the vacuum advance disconnected. Once the
mechanical advance is dialed in, connect the vacuum advance, and dial it in for
best *part-throttle* power with no pinging or surging. This last step is
universally omitted when the car magazines write about engine buildups.
A 2.56:1 rear is a pretty darn stiff rear ratio, which means the engine
sees a much bigger load (less torque multiplication through the rear gear).
A bigger engine load means increased cylinder pressure and increased
tendency to detonate. Translation: be cautious in going to lighter and
lighter distributor springs, as your engine is working harder than most due
to the very stiff rear end. Again what I've heard for Mopars is to use full
advance by roughly 2500 - 3000 rpm.
If you can get away with full advance
at lower rpm with no pinging, fine. Just be very careful not to run into
even mild "silent detonation" which can still break piston rings and damage
pistons without being loud enough for you to hear over the sound of the
car. Once you find the point where the thing pings, back off a few degrees
to give it a safety margin. Also a hotter day or a tank of bad gas might
come your way and needs a safety cushion. Better an engine a few % down on
torque than one that needs a rebuild due to detonation.
Race engines don't need vacuum advance, because they're never at part-throttle
anyway. Any street engine spends more time at part-throttle than WOT, and can
always benefit from having vacuum advance. Magazines like Hot Rod test engines
at WOT (Wide Open Throttle) on a dyno, where vacuum advance plays no role, so
they leave it off the engines. Then they tell you that you need 36 deg, or 32
deg, or whatever, of mechanical advance. They totally fail to inform you that
your engine will run better on the street with additional vacuum advance over
and beyond that 36° or whatever.
See the Tuning section for how-to details.
[ Thanks to John Carri, others
for this information. ]
Pinging
You have to reduce ignition timing; the only question is where, and by how
much. If it pings only under part-throttle, you can use an adjustable
vacuum advance unit to reduce the timing provided by the vacuum-advance. If
it pings under all wide-open throttle, you can back off total mechanical
advance by reducing base ignition timing. If it only pings at certain rpms
at wide-open throttle, you can use heavier springs on the advance weights
to reduce the rate at which the mechanical advance comes into play.
You might also have to change the jetting to compensate for the
vastly-different gasoline formulations available today.
[ Thanks to Bob Barry
for this information. ]
Spark Quality
Does a "hotter" spark realy create a faster burn?
"Hotter" isn't what you think. High energy ignitions allow the plug gap to
be increased, and also make "fatter" sparks. More spark surface area exposed
to the mixture makes for more complete combustion. The other main
performance item is the *duration* of the spark. Longer is better. Making a
long duration spark has practical engineering limitations. MSD found the
same results can be achieved with multiple short duration sparks.
Getting the chemical reaction started is the big deal. Once it has started
it will go as fast as it can react.
I don't believe they spark during the exhaust cycle, like some distributor-
less (DIS) ignitions.
Funky stuff happens during the first few microseconds of ignition. It's a
complicated thing. The flame can actually "blow" itself out under certain
conditions, and reignite an instant later. Power lost. "Hot" spark helps a
good deal.
[ Thanks to Dave Cullen
for this information. ]
Oldsmobile Distributors
Date Code
You should find a 3 digit alphanumeric
code which is the date-code (date of manufacture) of the distributor. An
example would be 1A7 where the 1= Year (1971) and the A=
Month (Jan.) and the 7=day of the month (7th). If it is the original
distributor, this code should correspond somewhere near the date your car was
manufactured. GM did not use I's in these codes because of
confusion between 1's. Otherwise M would be the 13th month which does not
exist, and again 7 being the 7th day of the month.
[ Thanks to Kevin Hoopingarner, Chris Witt
for this information. ]
Olds Distributor Specifications 1965-1975
- Chassis Service Manuals' listing of all numbers known.
- W-options may not be mentioned.
- All dist #'s from the OCSM's [Olds Chassis Service Manuals]
- L-6 [Chevy] engines not included.
- For a few of the hotter units, I included the advance curve specs.
Note that factory vacuum advance canisters generally are stamped with the last
3 digits of the part# and the total vacuum advance it makes, in degrees. E.g.,
the first 1965 unit shown should be stamped "210 16" if it provides 16°
of vacuum advance.
Dist # Vac Unit Applications
-1965-
1110322 1116210 All 33xx, 35xx series [Cutlass]
1111029 1116232 34xx-36xx all, 3855, 3865, 52xx w/L65 [L65= 330 LC]
1111048 1116232 3827, 3837, 3867, 52xx exc. L65, all L74 & L76
[U500003G, T500003G engine ID's 330-4V 10.25 CR]
1111042 1116232 54-86, 34, 36, 38xx w/L77 or L78
1111089 1116232 56-58 w/L65
-1966-
1111048 1116232 330 HC & L74, L76
1111048 [specs: VA begin 6-8 inHg, 9 deg @15.5-19.5 inHg.
Mech 0-2 @400RPM, 7.7-9.7 @1025, 14-16 @2000]
1111029 1116232 330 LC
1111042 1116232 400/425-2V HC
1111151 1115361 425-4V HC
1111151 [specs: VA begin 8-10 inHg, 9 deg @16.5-18.5 inHg.
Mech 0-2 @600RPM, 3.5-5.5 @900, 8-10 @2100]
1111089 1116232 425 LC
-1967- *= UHV or Capacitive Discharge Ignition System
1111048 1116232 330 HC & L74, L76
1111029 1116232 330 LC
1111042 1116232 400/425-2V HC
1111188 1116232 UHV dist'r for 400/425-2V HC
1111151 1115361 425-4V HC
1111179 1115361 UHV dist'r for 400/425-2V HC
1111089 1116232 425 LC
1111189 1116232 UHV dist for 425 LC
-1968- *K66= UHV or Capacitive Discharge Ignition System
1111286 1973406 350 LC
1111299 1115361 350 HC
1111466 1973407 400 LC
1111287 1973408 400 HC MT exc. W30
1111290 1973408 400 HC MT exc. W30, w/UHV
1111290 [specs: VA begin @8-10 inHg, 12 deg @18.5-20.5 inHg.
Mech 0.4-2.4 @500RPM, 8-10 @900, 10-12 @2000]
1111468 1973418 400 HC AT & all W30
1111468 [specs: VA begin @10-12 inHg, 8 deg @16-18 inHg.
Mech 0.5-2.5 @450RPM, 7-9 @1000, 9-11 @1900]
1111470 1973418 400 HC AT & all W30, w/UHV
1111288 1973407 455 LC
1111291 1973407 455 LC, w/UHV
1111289 1973408 455 HC exc. W34; also H/O with A/C
1111292 1973408 455 HC exc. W34, w/UHV
1111469 1973408 455 HC w/W34
1111471 1973408 455 HC w/W34, w/UHV
-1969- *No K66 [UHV ignition system] listed in CSM
1111961 1973408 350 LC
1111930 1115361 350 HC
1111933 1973418 400 HC AT & all W30
1111933 [specs: VA begin @10-12 inHg, 8 deg @16-18 inHg.
Mech 0.5-2.5 @450RPM, 7-9 @1000, 9-11 @1900]
1111932 1973408 400 HC MT exc. W30
1111932 [specs: VA begin @8-10 inHg, 12 deg @18.5-20.5 inHg.
Mech 0.4-2.4@ 500RPM, 8-10 @900, 10-12@ 2000]
1111934 1973407 455 LC
1111935 1973408 455 HC exc. W34
1111936 1973408 455 HC w/ W34
1111936 [specs: VA begin @8-10 inHg, 12 deg @18.5-20.5 inHg.
Mech 0-2@550RPM, 5-7 @1000, 9-11@1800]
-1970- *No K66 [UHV ignition system] listed in CSM
1111975 1115361 350-4V A-body AT, AT w/AC, MT, AT or MT w/W31.
[QN,QP,QV,QX,QD]
1111976 1973408 350-2V A-body AT, AT w/AC, MT [engines QA,QJ,QI]
1111976 1973408 350-2V B-body AT, AT w/AC, MT [engines TD,TC,TL]
1111981 *1 1973427 455-2V-HC A-body [TX,TY]
1111982 1973427 455-4V-HC A-body [TW,TV,TU]
1111979 1973427 455-4V-HC A-body AT w/W30 [TT]
1111979 [specs: VA begin @10-13 inHg, 4.2-7.3 deg @16 inHg.
Mech 0-3.5 @375RPM, 7- 10.3 @575, 14-16 @1500]
1111977 1973427 455-4V-HC A-body MT w/W30 [TS]
1111977 [specs: VA begin @10-13 inHg, 4.2-7.3 deg @16 inHg.
Mech 0.4-2.4@ 500RPM, 8-10 @900, 10-12 @2000]
1111981 *1 1973427 455-4V-HC Vista Cruiser AT [TQ,TP]
1111980 1973408 455-2V-HC B&C-body (88 & 98) [UC,UD,UJ]
1111981 *1 1973427 455-4V-HC AT B&C-body (88 & 98) [UN,UO]
1111982 1973427 455-4V-HC AT B&C-body (88 & 98) Police W-33 engine [UL]
1111981 *1 1973427 455-4V-HC AT E-body (Toronado) [US,UT]
1111982 1973427 455-4V-HC AT E-body (Toronado) w/W34 [UV,UW]
1111978 *2 1973430 All where 1111981 is used above
*1= 1st type, *2= 2nd type
-1971-
1112079 1973407 350 A-body [tune-up label OA,OB]
1112085 1973407 350-4V A-body [tune-up label OB]
1112079 1973407 350-2V B-body [tune-up label OA]
1112033 1973408 455 A-body [tune-up label OD,OF,OG,OK]
1112036 1973407 455 A-body [tune-up label OE]
1112034 1973407 455 A-body [tune-up label OE,OL]
1112033 1973408 455 B&C-body [tune-up label OF,OG,OJ]
1112078 1973408 455 E-body (Torondo) [Engine US,UT] [tune-up label OH]
-1972-
1112106 1973407 350-2V [code QA,QB,QC,QN]; 350-4V-MT [QD,QE]
1112085 1973407 350-4V-AT [QJ,QK,QP]
1112033 1973408 350-4V exc. MT/W30/Toronado [UA,UB,US,UT]
1112034 1973407 455-AT-w/W30 [UL,UN.UO]
1112036 1973407 455-MT-w/W30 [UL,UN.UO]
1112036 [specs: VA begin @6-8 inHg, 13 deg @16-17.5 inHg.
Mech 0.4-2.4 @500RPM, 8-10 @900, 10-12 @2000]
1112172 1973408 455-4V-AT Toro & MT [UD,UE,UU,UV]
1112033 1973408 455-4V-MT [UD,UE,UU,UV]
-1973-
1112226 1973468 350-2V L-32 & L-33; Omega, Cutlass [code QP,QQ,QS,QT];
"88" [code QN,QO]
1112195 1973453 350-4V L-34 AT (exc. wagon)
Omega, Cutlass [code QA,QB,QJ,QK]
1112225 1973453 350-4V L-34 AT wagon Vista Cruiser [code QU,QV]
1112222 1973453 350-4V L-34 MT Omega, Cutlass, V.C. [code QC,QD,QE,QL]
1112197 1973232 455-4V L-75 MT Cutlass [engine UD]
1112197 1973232 455-4V L-74 & L-75 AT Cutlass, 88, 98 [engines UA,UB,US,UT]
1112198 1973466 455-4V-AT L-78 AT Toronado [engines UU,UV]
-1974-
1112195 1973453 350-4V L-34 AT (exc. wagon)
Omega, Cutlass [code QB,QC,QL,QO]
1112226 *1 1973468 350-4V (Calif.) L-34 AT (exc. wagon)
Omega, Cutlass [code TB,TC,TL,TO]
1112828 *1 1973468 350-4V (Calif.) L-34 AT (exc. wagon)
Omega, Cutlass [code TB,TC,TL,TO]
1112550 1973427 455-4V L-76 [UV,UX] Cutlass
1112225 1973453 350-4V L-35 [code QU,QW] "88" cars;
L-34 wagon AT [QU,QW] Cutlass, V.C.
1112197 1116232 455-4V (Calif.) L-74 &L-75 AT [UA,UC,UL]
Cutlass, wagons, 88, 98.
1112531 1973496 455-4V (Calif.) L-74 &L-75 AT [VA,VC,VL]
Cutlass, wagons, 88, 98.
1112506 1973474 455-4V w/K-86 L-74 [UB,UD,UN] 88 & 98
1112532 1973499 455-4V w/K-86 (Calif.) L-74 [VB,VD] 88 & 98
1112827 1973497 455-4V-AT L-78 [UO] Toronado
1112825 1973496 455-4V-AT (Calif.) L-78 [VO] Toronado
1112830 1973500 455-4V-AT w/K-86 L-78 [UP] Toronado
1112829 1973499 455-4V-AT w/K-86 (Calif.) L-78 [VP] Toronado
1112172 *2 1973408 455-4V L-78 [VS] Ambulance, Hearse; [VV,VT] Motor Home
1112082 *2 1973408 455-4V L-78 [VS] Ambulance, Hearse; [VV,VT] Motor Home
417923 -none- 455-4V-LC [BA] Marine
417961 -none- 455-4V-HC [BC] Marine
1112228 1973430 455-4V [CE] Irrigation motor
NOTES: *1) 1112226 = 1112828; *2) 1112172 = 1112082.
-1975- including 400 Pontiac motor info but not 231 V6 or 250 I6.
1112951 1973556 260-2V (Calif.) LV8 AT (Calif.)
[code TE,TJ,TP,TT] Omega, Cutlass
1112956 -none- 260-2V (Calif.) LV8 AT (Calif.) [code TE,TJ,TP,TT]
Omega, Cutlass
1112896 1973525 Omega 350-2V L-32 (exc. Calif.) [RS,RT];
350-4V L-77 AT (exc. Calif.) [RW,RX];
350-4V L-77 AT (Calif.) [PA,PP]
1112936 1973531 350-4V (Calif.) L-34 AT
[code QL,QO,QX,QU,Q2,Q3,Q4,Q5] Cutlass, 88.
1112953 1973536 350-4V (Calif.) L-34 AT [code TL,TO,TX,TU,TW,TY] Cutlass, 88.
1112500 1116493 400-2V L-65 AT (exc. Calif.) [YH,YJ] 88 exc. Wgn.
1112928 1973493 400-4V L-48 AT (exc. Calif.) [YM,YT]
(YM= early prod.) 88 Wgns, 98.
1112958 1973514 400-4V L-48 AT (exc. Calif.) [YL] (late prod.)
88 Wgns, 98 sedans.
1112937 1973563 455-4V L-74 AT (exc. Calif.) [UB,UC,UD,UE] &
(Calif.) [VB,VC,VD, VE] Cutlass, 88, 98.
1112952 1973563 455-4V-AT L-78 [UP,U2] Toronado (exc Calif)
or [VP] (Calif.)
1112893 1973523 455-4V-AT L-78 [RA,RC] (exc. Calif.) Motor Homes
1112945 1973560 455-4V-AT L-78 [RB] (Calif.) Motor Homes
417961 -none- 455-4V-HC [ML] Marine
418482 -none- 455-4V-LC [MK] Marine
550360 -none- 350-4V-LC [engine MJ] Marine
1112228 1973430 455-4V [CE] Irrigation motor
[ Thanks to Chris Witt for this information. ]
Distributor End Play
Please be aware that the instructions on shimming the distributor shaft
for minimal endplay are *wrong* when it comes to Oldsmobile
distributors. Carl Dudash, who used to be on this list, pointed this out
about a year ago. I'll paraphrase his original explanation:
Chevy distributors turn clockwise, seen from above; consequently the
distributor shaft is pushed up, out of the engine block, by the angled
cam gear when the engine is running. To prevent exceeding the maximum
air-gap the Pertronix module can tolerate, Chevy distributors have to be
shimmed.
Olds distributors turn anti-clockwise, and are pulled downwards, into
the engine block, when the engine is running. The end of the distributor
shaft is actually pulled down into contact with an internal thrust
surface in the block. For this design to work, the distributor *needs to
have* some endplay; shim it and you'll eat up the shims and may damage
the distributor too. To set up the Pertronix module in an Olds
distributor, push down on the distributor shaft so it bottoms out in the
distributor housing, then set the airgap.
As another listee pointed out, Pertronix now has a better designed
system which no longer uses the cheesy warped plastic magnet ring, but
instead triggers off the cam that used to operate the points formerly.
This system is not sensitive to distributor shaft endplay, and is a much
more elegant solution IMHO.
[ Thanks to Carl Dudash, John Carri
for this information. ]
Ignition Types
Mechanical vs Solid State
It depends on if it is a mechanical or electronic (also called
"solid-state") regulator. While heat is definitely bad for all electrical
devices, whether mechanical or not, the firewall above the distributor is
usually cool enough.
A mechanical voltage regulator is just that -- mechanical. It consists of a
couple of relays, a couple of resistors, and (in some regulators) a diode.
In the mechanical regulator the armature is a flexible, spring metal arm
with contact points on the end. Like ignition breaker points, these points
can arc, corrode, pit, and accumulate deposits. Also, with the constant
flexing of the armature (many times a second), the relays may get to a point
where the armature no longer actuates properly. Also, the resistors are the
wire-wound type and may eventually burn through, or lose their resistive
tolerances, though that last item is unlikely. So, in a mechanical
regulator failure is often due to mechanical failure or similar mechanical
problem, like burned or corroded contact points.
An electronic regulator accomplishes regulation by means of semiconductor
devices (transistors, diodes, etc.). No mechanical action exists. As such,
they can be made smaller than their mechanical counterparts. Hence, it's
just convenient to install it in the same case as the alternator. However,
some manufacturers (Ford and Chrysler) initially just replaced their
external mechanical regulators with external electronic versions and made
little change to the alternator itself.
Failure in an electronic regulator can be due to heat. Severe short
circuits can also damage them. Then there's entropy. That is, everything
decays. The constant voltage handling can just eventual wear the
electronics out, in the same way an electronic ignition module just goes bad
or gets flaky. The transistors can eventually short or open. However,
electronic regulators do a superior job of voltage regulation and ensure a
far more stable power supply than any mechanical regulator could accomplish.
That's why they're preferred for HEI.
[ Thanks to Thomas Smith
for this information. ]
Points
The points are just a mechanical switch. The cam in the
distributor pushes open the points and spark happens. In an electronic
ignition, a solid state device takes the place of the points. No wear,
no adjustments required. And because of certain electrical advantages
(I'll spare everyone the techno-babble), electronic ignitions make a
higher voltage spark and perform far better at high rpm's than points
ignitions.
You need about 15,000 volts to fire a plug with a .035 gap. Higher
compression in the cylinder requires even more. Larger plug gap requires
still more. A larger gap means a longer spark, which helps combustion
effieciency by providing ignition to a bigger area of mixture in the
combustion chamber. This will help mileage, emissions, and power. The GM
HEI units provide about 30,000 volts. Bzzzzt.
When the points open, the condenser is
there to PREVENT the spark from continuing to jump the points gap by
absorbing the surge of current that results from the points opening. In
fact, if the system worked as you describe the ignition system would work
very poorly, if at all. You may note that electronic ignition systems do
not require a capacitor as this problem of current continuing to flow across
the points gap does not exist there. The circuit interruption is quick and
complete. Capacitors in electronic ignition systems work to prevent radio
interference only.
The way the system works is this. With the points closed, current flows
through the primary side of the coil to ground. The current level in the
primary side is being brought to that allowed by the entire circuit. This
takes time. As the current flows through the coil, it creates a magnetic
field which is concentrated by it's iron core. When the points open, the
magnetic field collapses in the primary which increases it's level to
hundreds of volts. That's right. Hundreds of volts will be felt by both
windings. A mere 12 volts is
not simply stepped up to the thousands required for a spark. It first
builds to hundreds as the magnetic field in the primary side collapses.
This voltage level is stepped-up by the secondary windings to thousands of
volts. It is this voltage which fires the plug.
Electrically, it's e = L di/dt, or voltage = the coil inductance times the
rate of change of primary current as the stored coil current discharges.
Calculus in yer Oldsmobile.
Now, if the condenser provided the energy for the secondary coil windings,
it would actually oppose, thus
slowing, the magnetic collapse in the primary winding as it would allow
current to continue flowing across the points, when complete stoppage is the
goal. This would create a very poor spark.
Besides getting virtually no spark, a missing or open condenser (capacitor)
will cause the points to burn out very quickly. Just take that as FYI.
However, for optimum
performance, the collapse of the magnetic field int he primary side must be
as rapid and complete as possible. Any sparking across the points gap slows
and reduces the completeness of the collapse. The condenser stores most of
the current that attempts to continue across the gap.
Note a few crucial facts. First, an ignition coil is simply an iron-core,
step-up autotransformer. Nothing more. Nothing less. As such,
transformers DO NOT work with direct current. The only reason they work in
a car's ignition system is that the breaker points (or electronic ignition
module) constantly and rapidly makes and breaks the circuit creating a
quasi-AC current. When the discharge (spark) begins, the coil secondary
inductance and distributed capacitance becomes a tuned circuit, and
resonates at some natural frequency. If you ever looked at a spark with an
oscilloscope, you'll see that it is in fact a high frequency ac signal.
That's why it can interfere with radio.
In fact, at 600 rpm, the frequency of the ignition
circuit in a V8 engine is 40 Hertz. In fact, it is this making and breaking
of the circuit which causes the primary current to be induced into the
secondary.
Second, since an A
C-type of signal is felt by the points, this is precisely
the reason the capacitor (the real word for condenser) works. Capacitors
act simply as open circuits to direct current, but they act as shorts to AC.
So, the instant the points open the change in current acts as AC and the
surge is stored by the capacitor. The charge stored by the capacitor is not
released until the points close again.
[ Thanks to Thomas Smith, Dave Cullen
for this information. ]
Dwell:
"Dwell" is the amount of time, as measured in degrees of rotation, that the
primary circuit of the ignition system is closed, allowing the ignition coil
to build a charge. In short, the higher the dwell, the longer the coil has
to charge. However, there are only 360° in a circle, so the more
time you give the coil to charge (higher dwell) the less time you allow for
the coil to discharge, firing the spark plug. The goal is to find the ideal
balance between the two.
Bear in mind, once an inductive circuit (i.e., ignition coil) has built to
its maximum charge, any more time allowed for charging is unnecessary and is
a waste. So, if only 30° of dwell are required to charge the coil,
allowing 38 degrees only results in 8° of wasted time that could be
used on coil discharge, hence, spark plug firing.
On the other hand, allowing too little dwell results in insufficient coil
charging which produces a weak spark.
Both spark power (wattage: voltage X amperage) AND spark duration are
necessary to promote complete combustion and efficiency. So, you need enough
dwell to provide sufficient spark power but not so much that you have
insufficient spark duration.
The points distributor will have a metal "door" which slides up and down
(normally down to close) so you can set the dwell for the points. The
points are normally closed to produce a field in the ignition coil. When
the points open, the field collapses. The energy of the collapsing field is
used to fire the plug. You need to have the points closed long enough to
produce a field in the coil.
Anywhere between .016 and .018 is correct for a starting point. This will
get the car started. Once that's done, the points should be readjusted
using a dwell meter as the car is running.
I had instructions years ago for easy setting of dwell:
Start with "about" 0.020" gap. Start motor. Turn points adjusting screw CW
until engine begins to misfire. Back out 1/2 turn.
I did this, then checked with dwell memter; it was right on the money. Optimal is
30°, acceptable range is +/- 2 degees.
Be sure to set dwell, THEN timing, as changes in dewll change the timing...
because the spark occurs when the points open. Change when they open [the
dwell], you change the spark time.
[ Thanks to Dan Lacey, Thomas Smith, Chris Witt
for this information. ]
Points for Performance:
First buy a recurve kit. Put the weights on and one light
spring and one medium spring. Next set timing at 10° to 12°. Next you
need to check total timing at 1800rpm's. Oldsmobiles like 36° for
this. Next replace the stock points with Standard Ignition Performance
Points. It has a heavier spring to stop floating of the points. I check my
plugs a couple times a year to check for fouling out or if the electrode is
wearing down. For your car, it depends on how much mileage you put on the
car. Check the rotor and cap once a
year for carbon tracks or burnt up tips. Wires replace when you feel the
wires are old and brittle. A good indicator is when the cap is trashed, so are
the wires.
[ Thanks to Mark Prince
for this information. ]
High Energy Ignition (HEI)
HEI is a big distributor that sits on the back of 1974 and later oldsmobiles.
The caps and rotors are noticeably bigger than points type distributors.
For reference compare the 1974 and up with the late 60s and you'll see
the height and diameter size difference in the units. Another way to tell
is that the points type distribs have the coil mounted separately on the
intake manifold, whereas in the HEI it sits on top of the cap. Both are
black if the caps are factory.
The HEI (high energy ignition), was standard on GM cars from about '75 up
till the change to fuel injection. Avoid the '81 up unless you have a
computer in the car. The distributor itself it pretty distinct. It's
larger in diameter than the points type, and the coil (about 3", cubical,
but usually covered by a plastic cover) is incorporated into the
distributor cap. They also came with a plastic "ring" that snaps on top of
the distributor that holds down the wires and has the firing order written
on it, although these rings are frequently gone. On the lower side
(usually driver's side) of the distributor cap are spade connectors for the
ignition, ground, and tach.
If you really want to be sure you can ID an HEI distributor, go to the
local parts store and look at the HEI distributor caps. They're certain to
have dozens of them out on the racks.
Reasons to use an HEI: First, the performance of a brand new points system
vs a new HEI may appear to be identical, but they are not. Some partial
misfires will occur, and any extremes such as temperature, gas mixture
variations, idle or max RPM, or less than perfect engine breathing will
increase these. I realize some will they can't feel any difference, but I
have found some "can't feel" differences may be quite obvious on a stopwatch. By
putting more energy into a wider spark gap, the HEI minimizes these effects. A
good aftermarket booster (I use Jacobs) will do even better
Second, the whole points system is marginal, and new parts start degrading
almost immediately. The cap and wiring are only up to the job when new and
dry; remember the wet ignitions, the sparks across a frosty cap and less than
new wires? For that reason an ignition booster may not do much good under
extreme conditions. The points ability to deliver maximum energy will start
degrading as soon as you drive it out of the garage; my high compression 63
Cutlass would be quite noticable after a few thousand miles. Wear on the
block can shift timing. The HEI system has enough margin built it to deal
much better with extremes, even with a booster. And instead of constantly
deteriorating, the HEI maintains a consistent superior level of performance
for a very long time
Third, maintenance. Since the HEI isn't stressed to the limit, there isn't a
constant need to change cap, wires, and plugs. And no points! I prefer to
sandblast and regap plugs at 15,000 mi, replace at 30, still a huge improvement
Fourth, simplicity. I always found the separate distributor, coil, and ballast
with low and high tension wires connecting things pretty annoying. The HEI is
a single unit with a single 12V wire. When troubleshooting, the whole system
(except plugs) can be popped out in a few minutes and another dropped in
[ Thanks to Chris Fair, Tom Lentz, Bruce Roe
for this information. ]
GM MISAR HEI Variation
I remember the 1977-78 ignition system on the Toros was called MISAR. They
are a bit of a strange HEI. The vacuum advance is replaced by an early computer with a lot
of extra wiring and sensors. I actually transferred one of these complete 78
Toro systems to my Delta 88 with the 403 engine. Later I found a simple 79
Toro HEI had exactly the same performance, so I switched to that
There is a standard way of putting in HEI so that connections line up, and
there is room for some timing adjustment. However in theory there are a
multitude of ways of putting it in a non-fuel injected engine that will
work. The critical thing is that the rotator points to the correct wire at
the correct time. The gear has 19 teeth, so there are 19 ways to insert the
shaft. Sometimes things hit when the HEI is rotated to set timing, so I just
pull the whole thing, rotate everything 1/19 in the direction to give more
room, and set timing here
For any orientation of the HEI rotator, there are 8 possible positions for the
body (for a V-8). However the plug wires must maintain a fixed relation to the
rotor, so they would be moved from hole to hole on the cap. The cap is keyed
to only go on the base one way.
[ Thanks to Bruce Roe
for this information. ]
GM Capacitance Discharge
In 1967 Oldsmobile introduced a Capacitor Discharge
ignition system. Option code K66. This was available
on the 400 (including W-30) and 425 engines. Although
I do not believe this was a factory option on the
330's, it certainly could have been added by the dealer or
installed with over the counter factory parts.
The UHV, (Ultra High Voltage) system is an early
electronic ignition. These utilized a magnetic pickup,
which was triggered in a similar manor as an HEI.
Although they were (are) a reliable system, it was
not a particularly popular option. (Perhaps people
preferred points/cond. over this new fangled
electronic stuff). It was discontinued in 1968.
This system first available in 1967. This truly was the
forerunner of HEI, using the same magnetic pickup in a
standard small (points-style) Delco distributor. The
electronic control module was an MSD-sized unit mounted to
the inner fender, while the coil looks like a standard Delco
external "points-style" coil, however it is different
internally and painted red instead of black. I think UHV
was available at least through 1969.
If you are planning on purchasing the setup, be sure
to get all of the pieces. As some individual components
are getting somewhat hard to find (read $$$).
This includes the special red coil. A similar system
was used on late 60's Corvettes. And was more popular
with the Vette buyers. Consequently, some of the
distributors internal components are available through
suppliers of Corvette parts. Although Olds used a
different amplifier than the Corvette, they can be
repaired by anyone who does the Vette repairs.
Spark plug gap was increased to .045 with the
UHV system.
[ Thanks to Greg Rollin
for this information. ]
Aftermarket
The benefits of high performance aftermarket ignitions in stock, low compression
setups can vary. Sometimes the benefits are negligible. For instance, a book I
have on electronic ignitions indicates that stock low compression setups often
only demand 6,000-8,000 volts from a coil, regardless of it's advertised
output. In fact, advertised output is just that -- ADVERTISED. It is a rating
that is usually only realized in a lab. I have that on the word of a tech at
MSD, itself.
However, hipo ignitions can provide the extra punch necessary to fire high
performance, high compression, dense mixtures. One thing they all have in
common is electronics. Some are analog, some are digital. However, the
precision offered by the electronics produces much cleaner current switching --
allowing greater coil efficiency, and much more precise timing than could ever
be achieved with points. So, I think such systems are often a good idea in
replacing points, even in a stock installation. Their benefit over a stock GM
HEI is much less significant than points, however. Many folks insist, though,
that they noticed an improvement when they hooked an MSD up to an HEI.
What they do varies with design. Some increase spark duration for a more
complete burn. Some, like the MSD fire multiple sparks (actually, MSD is an
acronymn for Multiple Spark Discharge). Most advertise at least some increase
in spark current, which will produce a higher wattage spark making for a hotter,
fatter spark. One of their main benefits, especially when compared to points, is
more consistency against misfiring. Many also incorporate rev controls and
adjustable timing.
My guess is that if you already have an HEI, just the MSD would be all you
should need to add. Installing a remote mount coil (to keep it cool) and using
a higher output coil, if you're running high compression would also be helpful.
[ Thanks to Thomas Smith
for this information. ]
Upgrade Cautions:
One point seems to be getting lost in some of the responses tho. There is no
way that Mallory, Pertronix or any other aftermarket mfr can come close to
the development investment by GM and the experience of millions of systems
installed. The only systems that can claim even a smidgen of that are those
that have been out there for many, many years. And by aftermarket
definitions, they are probably already obsolete and have certainly been
"updated" based on the experiences of us, the people who paid money only to
have them crap out. Ask me about the adjustable timing device by a big name
supplier I bought some years ago. It was so good, as near as I can tell, it
isn't offered anymore. When it failed, the backfires it caused cost me damn
near the entire dual exhaust system on a motor home! Now that was an
expensive R&D effort - for me! Not to mention that the episode scared the
hell out of the wife who was afraid to even get back into the beast. These
kinds of experiences I don't need.
If you store you prized classic Olds in a place where the points are going
to deteriorate at such a rate that they become unreliable in a short time,
you have much bigger problems to worry about than frequent tune ups! Points
just are not that unreliable. They work quite well actually. Obsolete
doesn't mean it doesn't work. Carburetors are obsolete too, but don't tell
Holley, Carter, Edelbrock, etc.
If it was my car and I wanted stock appearance, and I drove the car any
distances at all, I'd run points. Or buy, and carry at all times, a second
version of the solid state gizmo I used to replace them. That's a pretty
expensive alternative to points which are probably, admittedly IMO, more
reliable than the gizmos.
I definitely do not like being stranded in the middle of nowhere with
equipment that needs a well stocked specialty store, or for these items
maybe a phone order catalog, to get the parts I need to get up and running
again.
Kurt Heinrich has noted OAI systems can clear the HEI. A friend of ours has
a 69 Cutlass (non OAI) with an HEI, his barely clears and he had to put a
piece of heater hose between the HEI and air cleaner. It was arcing to
ground. Now that's a SPARK! He shows his car at OCA National Meets and
hasn't been dinged for the HEI yet - it can't be seen under that big air
cleaner!)
If it was my ~70's OAI air cleaner and clearance was a problem, before I
used a F*rd service tool on it
I'd look at possibly using a non-OAI base, just for cruising. They fit, are
easy to find and are cheap. Paid $5 for the last one I bought.
Since I run an Edelbrock Troker intake on my 67, there's no clearance
problem with the HEI, like an inch and a half to spare! The problem is the
OAI air cleaner interferring with the hood - which is what originally
spawned the scoop you can see on the Bryceman's page. I wasn't about to give
up my OAI shroud either!
The point of my comments were to point out the reliability of the HEI versus
aftermarket stuff. I am a firm believer in doing what you like to your
car. Neither of ours are offerings to the gods of correctness. Like I used
to post at the end of my messages, "Enjoy The Ride!" (Too bad it wasn't a
US mfr who coined that one.)
BTW, dual points used to be the "hot setup" way back when, and single point
systems were "obsolete". WHAT A PAIN IN THE #$$% they were!
Here's something to think about with light sensing distributor set ups. If
this is strictly a race car or show car that only goes out in nice weather.
then thats fine. But if this is a daily driver, don't be suprised if on
cool damp days the car runs poorly...or not at all. This is due to
condensation refracting the light beam. Try diagnosing that one when it
happens. Car starts...runs fine for the first few minutes then either
starts missing or stops altogether. 10 min.s later repeats the cycle.
Been there many moons ago with a 68 AMX....not fun.
Pertronix is one approach, also consider the MSD and similar Mallory systems.
You can hide the control box, if you want. Since the points are only used
to trigger the unit you've still solved a problem by cutiing the amperage
across the points to darn near zilch. The current flow is what eventually
kills a points set.
[ Thanks to Bob Handren, R. Kevin Noon
for this information. ]
Stringer
Also, for those of you who want to keep the stock look of a points-style
distributor without the hassle points can be, check out the Stinger ignition
system. It can be installed so that it's practically invisible, yet has the
modern convenience of electronic ignition. Call Dave or Karen at Dave Smith
Engineering (909) 371-7040.
I have used the Stinger system on both street and circle-track Olds engines
with real good results. It could be hidden for that "untouched stock" look,
since the trigger box (ignition control) is small. MSD ignition boxes will
work with the Stinger-equipped distributor as well.
Dave Smith Engineering sells a kit that replaces the points with a magnetic
trigger and a box to control the coil. Everything's bolt-in after you
install the kit on the distributor. I had one on my race car in '92 and used
one on the street until the distributor's bushings wore out. That's the only
caution I'd post about it, be sure the distributor's bushings are in good
shape before you install the kit. It uses the stock coil (most hi-perf coils
will fry the box) and everything else that the points-type unit did, making
it a low-cost alternative to points. Contact Dave Smith Engineering at
(909) 371-7040 (Corona, CA).
[ Thanks to Ken Snyder
for this information. ]
Pertronix
Just did this on Quincy's new 455. I used the PerTronix conversion. It came
with two components. The trigger that replaces the points and a circle of
magnets. The rebuilt engine came with a point distributor because an HEI
wouldn't fit with this Offy intake. It's real simple to install.
Unscrew the points, and remove saving the screw. Now screw down the
electronic trigger in place of the points. In my case there was a vacuum
advance screw head in the way of the electronic trigger mounting bracket
from mounting flat. I needed trim a notch in the trigger mounting bracket
for the screw head to fit into. This did immediately void my warrantee but
without cutting this notch, there was no way the trigger was going to mount
flat. The screw head was part of the mounting structure for the vacuum
advance system under the points plate and could not be removed or relocated.
You can run the triggers two wires through the distributor caps points
adjusting window and out to the coil. You can also run the wire down through
the distributor and out the hole the original points wire ran. This will
probably require removing the distributor to do so I suggest for at first
you run the wires through the cap metal window until you've run the
electronics a bit. Make sure it's installed right and runs OK with the new
components. The wires simply go to both the positive and negative posts on
the coil.
Remove the rotor, and than the screws from the rotor. The ring of magnets
slips over the mechanical advance weights and platform on top of the rotor
shaft. Than screws up to the under side with screws supplied. these screws
go up through the advance weights platform and through your rotor holding
the whole assembly together. There is to be between .010 and .060 of
clearance between the magnet ring and the trigger. The kit supplies spacer
washers that you install above the magnet ring and the advance weight
platform to drop the magnets closer to the trigger.
Use the original Positive electrical feed for the distributor. Use the
original coil for the points system as if it required a ballast resistor it
will probably already be on the positive feed for the coil. If you use a new
coil you will need test it to see that it has 1.5 ohms of resistance. If not
you will need buy a ballast resistor and install it. This is very important
as without this resistance either within the coil wiring or via external
resistor, the electronic trigger will burn out. You should be able to take
your new coil to a Radio Shack to test for proper resistance. Most repair
shops have an Ohm meter and can also test the coil.
Except for finding someone who could use an ohm meter, This was an extremely
simple conversion. I've yet to pull the distributor to run the wires through
the original points wire hole. The whole process didn't take 10 minutes. It
sounds much more complicated that it is actually.
My PerTronix system cost just under $60. Personally I prefer it to the
unilight as the unilight requires a beam of light that can be effected by
moisture and heat. The magnet trigger system of the PerTronix doesn't have
this problem. Not to mention that the Unilight system costs about 50% more
than the PerTronix system.
There are two styles of the Pertronix for GM vehicles. The
older style uses a magnet ring and the newer, easier style uses a lobe
sensor. It seems as if you have the older, magnet ring style. Now, to your
question:
The Pertronix instructions stating that you need to shim an Olds
distributor are wrong.DO NOT shim
an Olds distributor, you'll chew up the shims and maybe the distributor
and/or cam gear too. Just push the shaft down lightly when you're setting
the air-gap.
The advice to remove the distributor applies
to engines, such as Chevrolet, which acutally force the distributor
shaft up as it spins. This
necessitates installation of some shims between the drive gear and the shaft
housing to keep the shaft from riding up too high. However, you're in luck
because you have (drum roll) an OLDSMOBILE! Since Oldsmobiles spin the
distributor the opposite direction of Chevrolets, they pull the shaft down,
usually negating the need for shims. So, the air gap won't change. You
should be able to install the kit without removing the distributor, but it
is easier if you do remove the distributor. You
will, however, still need to make sure the air gap is okay.
Follow this link for more information:
http://www.vintageperformance.com/retrorockets/gm.htm.
[ Thanks to Gary Couse, Thomas Smith, John Carri
for this information. ]
Points to HEI Ignition Conversion
Overview
It is clearly superior (to me) for the following reasons
- Smoother idle.
- Better economy, slighly more power.
- Reliable so long as you stick with GM, not aftermarket, parts.
- Reliable so long as you keep an extra ignition module in the
glove box.
- No points to adjust or dwell to scr*w with ever.
- Fun swap.
- Bolt in mechanically, though wiring changes are required.
- More modern. If the GM engineers had found points were better
they would have stuck with 'em.
Cheap, it simplifies tuning, reduces radio noise, smooths the idle,
and provides more consistent timing on the top
end. No drawbacks except it costs $40 bucks or so in the junkyard and
maybe $200 for a new one. Get the air cleaner assembly from an
HEI engine as well, as the original air cleaner will hit the HEI
distributor cap.
Simply put, in the old days (points) there was a resistor used to drop
the current availble to the ignition during normal running conditions to
prevent the points from burning out quickly. For starting, the resistor
was bypassed so you could get a nice, "hot" spark for easy starting.
The HEI does not need this current reduction, and it can acutally be
harmful to the HEI module if it is run thru the resistor. Therefor, the
HEI needs just to be connected so that it receives a full 12 volts in
either of its to states - running or starting.
You hit it right on the head (ouch!). The module in the bottom of the HEI
does the same thing the points did in the old days, only now it's all
electronic and unlike the points it's non-adjustable for dwell degrees. But
you'd be hard-pressed to find someone who switched back to points after trying
an HEI. The units do a fine job, even straight out of a salvage yard - did
that on Grace when she was a street stock. You can run more plug gap, and in
turn have less chance of plug fouling, even though I can never remember
fouling out an Olds.
What we are doing on Grace now is using a computer-controlled HEI. These
units don't have vacuum or mechanical advance, which we don't want on our
circle track engines. The MSD system wires hook up directly to the pick up
coil in the bottom of the housing, and route out to the ignition box (to give
you an idea of how much more powerful MSD boxes are, remember that the red box
takes the place of the module that's usually in the bottom of the housing),
where it's processed to the coil (and tach) and then to an external coil. MSD
also sells an adapter that allows you to attach that external coil through the
HEI cap.
The benefits we get from the HEI system is simplicity, reliabilily, and plenty
of spark! We particularily like the large cap, it keeps the spark from arcing
to the wrong terminal inside the cap.
The only disadvantage of the HEI is the lack of a rev limiter. I guess
you could deem point bounce a rev limiter.
Stock HEI is not intended for high RPM (5000+ RPM), but upgrade modules are
available for such applications. Beware of coils that advertise more voltage
(at the cost of less current), what is useful is more energy. The breakover
and ionized voltage will be determined by the geometry of your combustion
chamber; the ignition can only control the current. HEI are available with
computer controlled advance; I would only use one if converting to electronic
fuel injection
Factory Option:
HEI was offered as an option on 1974 (available in last half of 1973)
Oldsmobiles, and became standard in 1975. Sales literature and parts
catalogs all indicate this.
For 1973 models a "unitized" ignition system
was offered. From the illustrations it looks similar to HEI (coil in cap,
etc.) but with some differences.
[ Thanks to Bruce Roe
for this information. ]
Technical Overview
HEI Types:
This non-computer controlled version (used 1974 - 1979) is referred to
as the 4-wire HEI, as there are four wires (or connectors) that attach
to the module. It also uses a vacuum advance pot. In Canada, carbureted
V-8 (haven't checked V-6's) models didn't receive CCC until 1986.
Therefore, some Canadian '80-'85 models could serve as HEI donors.
A 5-wire HEI was also used for a few years.
The fifth wire exits the dist. on the opposite side from the usual wires,
and this one still has the vacuum advance. Indications are that the 5th
wire goes to a special knock sensor. This sensor module instructs the
HEI module to retard timing if knock is detected.
This is a pre-computer attempt at timing control.
I think the system you are referring to is known as ESS (Electronic Spark
Selection). Basically, the ESS decoder advances or retards the spark
curve in response to the following inputs: engine vacuum, coolant
temperature, crank signal. A delayed spark is desirable during
cranking to reduce the load on the starting system, especially on a hot
engine. The spark is advanced above the normal setting during cruise
conditions, identified by a high manifold vacuum and greater than 1350 rpm
(1200 for some) engine speed. The spark isn't modified during other
conditions. The preceding is from a 1980 Cadillac service manual.
Olds V8's didn't receive a knock sensor until '88.
There is also a 7 wire HEI distributor and module used on later computer
controlled cars. This HEI has no vacuum advance pot as the computer controls
that function. The 7 wire HEI was used in Olds models from 1980 to 1988
(Cutlass), and possibly 1990 (Custom Cruiser). Probably any carb equipped
engine within these years is a donor for this 7 wire HEI. Modules don't
interchange between 4 and 7 wire. The 7 wire are more expensive as well.
The HEI coil is different from 1974-75, 1976-79 and 1980-onward.
Basically in the resistance of the secondarys.
The GM service part for the wire harness from the coil to the module
was updated at some time. The newer harness (p/n 1892261) has a
moulded plug for the module instead of seperate spade terminals and
has the capacitor built in.
HEI to use:
When replacing a points distributor, you will want to use the 4-wire HEI
found on 1974 to 1979 vehicles. The same Olds HEI or points distributor
will drop into a 330, 425, 350, 455, 403, 260, or 307.
All 1964-1990 (except 394) Olds engine
distributors interchange, including points distributors. Since, each GM
division used a distributor with unique shaft dimensions, you will need
to get one from an Olds engine to work in an Olds engine. Buick for
Buick, etc. The aluminum shaft of the distributor is unique for Olds,
having distinctive shapes to parts of the shaft. It usually has some blue
overspray on the shaft as well.
In regards to which
HEI is more performance oriented, well, you'll have to figure that out
yourself, but in general, they are all about the same. For more performance,
the distributor will have to be recurved. See the Tuning
section.
There are lots of HEIs in the salvage yards for cheap. A 1979 Firebird 403
would be good; a 1979 Toronado 350 may have a better curve. Grab the wires too
if converting (for 12V and tack). A lot of places have rebuilt ones; a few
build them from scratch (translation: expensive). Get new plug wires and cap
at least. Probably some work will be required to clean, lube, and recurve them.
Number of Wires Needed:
Since the points system uses a start circuit (full
12 V) and a run circuit (with resistance in line) there will actually be
two wires. You must replace the resistance wire with a standard wire (or
bypass the resistor wire) to ensure a full 12 volts to the coil at
all times. You end up connecting the start and
run wires to the single connection on the HEI. So there is only one connection
but both ignition wires on that connection.
Coil:
The coil sits in the top of the HEI distributor cap.
Grounding:
The body of the distributor still contacts the block, but the hold down
clamp and bolt act as the primary ground. There's also the cam gear, oil
pump shaft, etc. There are plenty of places to act as a ground.
Hooking up a Rally Pac:
This gets connected to the "TACH" terminal on the HEI coil where the rest of
the wires connect on the HEI coil. You will find the words "BAT" and "TACH"
topside of where to connect your tack wire. Use a spade terminal. Aftermarket
tacks are plugged in here also.
Distributor Shaft Free Play:
There should be a little play, but rule of thumb, the less play the
better. If you hold the body of the HEI in one
hand and grab the drive shaft in the other I get about 0.05" - 0.1"
of axial motion. Check the mechanical
advance weights and make sure they are free. WD-40 to the rescue again!
Although you do want to wipe up as much WD-40 as possible to keep from
attracting dirt.
Testing the HEI Unit Before Cutting Wires:
Just to test the thing out before patching in wires and disconnecting
others, you could just swap in the HEI and run a jumper wire straight
to the (+) positive battery post. It shouldn't hurt to drive around
the block a few times. You won't be able to shut off the engine unless
you add a switch to your jumper wire. But you shouldn't be worrying
about patching wires. This upgrade will benefit you tremendously. Just do it.
Maintenence and Replacement Parts:
I've heard alot of people say they don't trust the HEI modules since they can
just go, but just keep one in the glovebox as a
spare. And alot of people will also tell you that with points at least I
can see what's wrong, etc. but with most electronics today, it's not a
problem normally (you didn't buy cheap stuff, and save money, right?), and
any problem with the units when they came out (heat, vibration, unreliable)
has been worked out over the years. There are also millions of spare parts
available for these units everywhere.
Distributors wear out like everything else; it takes a lot longer
if they are properly lubricated. The oil rail (in an Olds) for the drivers
side valve lifters ends just before the distributer. It should have a pipe
plug with a .040" hole to spray oil on the distributor gear. If someone put
in a plug with no hole, the gears and lower distributor bearing will have a
short life. The lower bearing must take the strain of driving the oil pump, and
it may be worn oval shaped. Fortunately it can be replaced, but a special size
reamer is needed to finish it (yes, I have one). The upper bearing will have a
long unstressed life, providing you repack the grease cup around it at reasonable
intervals. Because of the pickup coil retainer groove and lube holes, the only
satisfactory replacements I have found are used ones from a "donner" unit (like
a Pontiac or Chevy). If the pickup coil is so old the insulation on the wires
is cracking, a new assembly can be purchased. Napa has them, but Rasco is a lot
cheaper. Weight pivots tend to wear; I put a tiny bit of brakelube on them
frequently to slow this down. If its too late, there are pivot repair kits (an
oversized plasic bearing over the pin). Last resort is a new shaft assembly. The
cap and wires have a long life, esp if you use premium parts. However I would
not try to run the same set over the life of my car (300,000+ mi). I run coils
and modules until they fail, a rare event.
Clearing A Dual Snorkel Air Cleaner:
If you need a dual snorkle to clear the HEI, get a 74 dual snorkle. Designed to
clear HEI. Hard to find but at least you don't have to ruin another.
The '76 Toro distributor is designed to have the cap mount 180° off.
As long as it is set up as it should be in a '76 Toro, all will be well.
My suspicions are more on the line that the module (you mentioned that a new
one had been put in) is the generic "all except Toro" module instead of the
correct one for the '76 Toro distributor.
Costs and Time Required:
This should take no
more than 2 hours, unless you have that great combination of 455 and
A/C, in which case you will have to add 4 hours to get to plug
#8. Just kidding, it is quite easy to get to from underneath.
~$50-$100 and one hour, to install a junkyard HEI.
~$80 and one hour, to install a Pertronix Ignitor.
~$150 and one hour, to install a Mallory electronic conversion.
~$250 and one hour, to install an aftermarket electronic distributor.
Add another hour or two (or three or four or...) if this is your first time
replacing a distributor and working with automotive electronics.
I spent about $220 in total. Time was about 4 hours total. Would have
been about two hours less if I hadn't spent so much time trying to
make it work with only a "run" position 12V source.
| Distributor | $150 |
| Coil, cap and rotor | $25 |
| R46SX plugs (AC) | $16 |
| HEI wires | $25 |
| Cap and plug from junk yard | $5
(took the cap just to get the ground strap under the coil). |
If you want to chance a junk yard distributor you can probably get it
(complete), for less than $40.
Oh, and if you don't already have an internally regulated alternator,
you'll need to buy one of those. I think they're about $35 to $40
rebuilt (usually with $15 core charge rebate).
Even with all new parts it was worth it to me.
[ Thanks to
Bob Valentine, Ken Snyder, Fred Nissen, Bruce Roe, Mick Gillespie
for this information. ]
Early Olds Rocket Engines:
No HEI unit will fit because the 1949 - 1964 303, 324, 371 and 394 engines
are physically different than the 1964+ Olds V-8's.
[ Thanks to Bruce Roe
for this information. ]
Sourcing Parts
Salvage Yard:
I'm in the middle of gradually accumulating HEI components now for my own swap
(although I may still end up not doing it). Here's what I have discovered. I
don't think newer ones are a better quality, per se, just more likely to have
fewer miles, which is important. Get the distributor that has the least number
of miles on it. All the internal electronic parts are replaceable and are
available from SuperCars Unlimited and Year One. The main worry about the
distributor itself is wear of the bushings and shaft, which can be expensive to
replace. As for comparing '75 and '76, I ~believe~ the internals are the same
on those two. The FAQ lists differences in ignition coils for different years.
I know, for example that there are coils that have red, black, and yellow wires
and others that have red, black, and white. I think the main difference among
those is in the resistance of the primary circuit. If anyone can comment on the
better of the two, I'd be interested.
After taking my distributor to the shop to have the lower bushing
made, I want to pass a word of warning along. Maybe some of you know this, but
I just learned it. That lower bushing is the first thing to physically go in
these distributors. And it ruins the shaft. Cost me $35 to get the bushing
made and pressed in, but I still have to come up with a new shaft (computer
ones, unfortunately, have a slightly different set up on the top) that I
didn't know about until I pulled it apart completely. What a disappointment. I
will now be careful to check that on every distributor that I pull.
If you go with a junkyard, GM HEI, make sure everything is working.
The best bet is to get a new (rebuilt) one and also buy a new cap,
coil and rotor. Oh yeah, get the connector for the 12v source and the
tach to plug into, and also the ground strap that fits under the coil
(this doesn't come with a rebuilt unit). So you'll have to go to the
bone yard. If you grab the whole cap, it's easy to see how the new
one should hook up and they probably won't charge more than $5.
Mick Gillespie
[ Thanks to
Mike Bloomer, Thomas Smith, Dorian Yeager
for this information. ]
Conversion Procedure
I'm convinced, give me the steps to convert!
Installation procedure is as follows (details follow this list):
- Remove the old distributor.
- Install the HEI unit.
- Change plugs to HEI resistor plugs.
- Change plug wires to HEI wires and install them.
- Sort out the wiring, and Perform the electrical hookup.
- Start the car and set the timing.
- Perform some might-as-wells..
Remove the Old Distributor:
The installation of the HEI unit will be easier if you turn the crankshaft
so that cylinder #1 is at TDC and index the outside of the HEI housing.
You will also remove the coil, plug wires and wire from the starter
solenoid stud labeled 'R'. This wire is specific to points ignition. It
feeds 12 volts to the points when the starter is turning, and the 'S'
solenoid stud feeds 9.6 volts while the engine is running. HEI runs on 12 volts
whether in run or start.
Always remove the low voltage wiring from ANY distributor before
pulling it. Otherwise a spark could occur when the shaft separates from the
block at that location, possibly causing crankcase fumes to explode.
Bring the engine to TDC BEFORE taking out the old distributor. Do
it by taking off the dist. cap and jogging it over until your rotor
is pointing at #1 spark plug wire position. Confirm that your timing
mark on the balancer is also close to the 0 deg position on the timing
plate. If you can't see the saw cut, it might mean that the balancer
has to be replaced, or a repair sleeve installed. It might also mean
that your timing was out a mile to begin with.
When you install the new distributor, all you have to do is line up
the rotor at #1 position and drop it in. Try to keep the vacuum
advance cannistor in roughly the same position as the old one.
This is a whole lot better than trying to find TDC with your thumb
over the #1 spark plug hole.
The majority of the problems are due to a hardened O ring on
the dist shaft combined with a build up of "gunk". On ones
that are particularly stubborn, try working in some kind of
solvent like carb cleaner. By working it back and forth it will
give the solvent a chance to loosen things up. Also make
sure that the dist shaft isn't binding against the cam gear as
it comes out. It will have to rotate backwards about 1/4 of
a turn before it disengages from the cam.
The problem will be that the oil pump drive rod, which is held in place in
the block by a washer, is also stuck in the bottom of the distributor. It's
a hex-shaped drive rod, and the bottom of the distributor has a 5/16"
hex-shaped hole (yeah, I guess you could use an Olds distributor as a socket
wrench...), and the points of the drive rod eventually get worn into the
flats of the hole.
Try grabbing the distributor shaft
and pushing back and forth. Then yank the distributor up and down. Now
try pulling the distributor up and out of the block. This should get most
distributors out.
If not, try a lot of yanking and tapping. Try tapping on the top of distributor
drive shaft (remove all parts above the shaft itself) with a drift punch,
yank up on the distributor a couple times (it should move up about a
¼"-½" or so, doesn't it?), tap some more, yank some more,
tap, yank, tap, yank, and so on, until it comes free.
One of two things will happen: either the oil pump drive rod will loosen up,
and you'll be able to pull out the distributor alone, or (more likely), the
washer retaining the oil pump drive rod will come loose or break, and settle
in the bottom of your oil pan. If the second happens, don't worry, the
washer will just sit there, perhaps adding to the stuff already clogging
your oil pump screen, but not enough to hurt anything, and you can just drop
the driveshaft back into the block (the rod will stay in place fine without
the washer).
Install the HEI Unit:
Hopefully you turned the engine over so the #1 cylinder is at TDC, and marked
on the firewall where the old points rotor was pointing. If not and the
points distributor is still in the block, do that now.
Put the HEI distributor in the hole, and line up the rotor with the firewall
mark. Wiggle the distributor a bit to get it to seat in the hole. Now check
cleanences with the firewall. The advance unit should not be right up against
the firewall. Try about 1" or so in order to initially fire the engine. You
will set the timing more accurately later.
Change Plugs:
When I converted my 1970 Cutlass to HEI, it ran badly until I regapped
the plugs from 0.030 to 0.065. I had newish platinum plugs and figured I'd
give the old ones a try.
If you have converted to HEI, you might notice a shortage, or absense
of spark plugs for your Olds engine. An appropriate substitute is AC-Delco
R46SX. When using R46SX plugs, the book says to gap them at .080" but
try .060". It make a difference in power with no harmful effects.
I found out today that the SX series of AC plugs has been
superceded by the SZ series and a local NAPA store was able to order them
for me.
With the MSD you might try getting something a bit heavier duty, perhaps platinum
or if they make the "truck plug" version of the R46SX.
If you are using the MSD 6AL box, I would recommend NGK 5670-6
spark plugs. They are like the NGK X45 but a little better. These plugs
are set at .040" gap. Make sure your timing is set
at 36° total. The inital advance should be around 18° if you installed
a recurve kit. If not, buy the kit, and put on one light spring and one
medium spring, and that will get the timing close.
Basically you run the largest gap possible.
The larger the gap, the greater the voltage required to jump the gap.
The greater the voltage - the sooner the leakage - the sooner the
cross-fire etc.
Bottom line, with a stock rotor, your pretty much stuck with the stock
gap. HEI systems can take up to a .060" or even larger gap. Most
engines are good for about .035". Higher cylinder pressures will require
higher voltages to jump the gap - you might need to upgrade wires to
accomplish this without cross-fire.
I have experiemented with gaps - going from .025" to .060" on a stock
system. The car basically ran the same. With the .060" gap it
sometimes misfired at idle and high rpm. The factory manual calls for
.035" and .045" works fine. Without dyno testing I couldn't tell what
was optimal.
I guess the standard ignition system rules apply - if it fires all
cylinders under all conditions than don't mess with it (save your time
and money).
Don't reduce the resistor spark plug gap to that of the non-resistor plug
gap (from .060" to .030"). This
prevents the HEI from providing its best advantage, a hotter spark.
Electricity will jump to ground as soon as it can. The smaller gap reduces
the voltage in the spark to no better than the points setup.
[ Thanks to
Mark Prince, Tom Lentz, Scott Parker, Bruce Roe, Dirk
for this information. ]
Change Plug Wires:
The wires from your points ignition are for non-resistor spark plugs,
while HEI uses resistor spark plugs and wires. For a bit more than generic HEI
replacement wires, you can buy a set of performance resistor HEI
compatible wires.
Sort out the Wiring and Perform the Electrical Hookup:
The HEI cap has 4 connectors. 2 are taken up by a connector from the
distributor. One is for the TACH, and is so marked. The last one is
marked BAT, and that's where you feed it 12v. Mine is wired straight from
the fusebox to the HEI, but you can use any 12v source which is activated
by the ignition key. I am sure there are "prettier solutions than going
through the fusebox, but I was in a hurry and that was the easiest way to
do it. You could also use this as an excuse to install a hidden kill switch.
The only wiring involved is finding the switched 12v source (hot with
ignition key in "START" and "RUN" positions) and running a
wire to the HEI BAT terminal.
The existing points distributor wire contains a resistor wire, which
knocks the voltage down to 9.6 volts. Follow that wire back to find
out either 1) where to eliminate the resistor, or 2) which wire not
to use. If you eliminate the resister, you can use that wire to supply
12 volts to the coil. If you decide to leave the wire alone and
patch in a new wire, just disconnect and safely secure the bare ends
of this points distributor wire. Maybe put some shrink wrap tubing
on the ends.
Just don't splice into the points supply wire and use it
for the coil. HEI needs a full 12V. You need to get rid of the resistance
wire completely. You also need this HEI supply wire to be hot, both for cranking
and in "run" mode. You can't use an alternator wire for this. The easiest
way is to follow the "resistance" wire into your fuse block. It
plugs in to the position marked "IGN" with a spade connector. Just plug
the HEI supply wire in that position, removing the points supply wire.
This gives you all the connections you need except the tach.
Plug your tach into the HEI in the position marked "Tach".
You also need to disconnect or remove the Hot wire from your
starter that connects to the old coil.
Finally, clean all of your electrical connections thoroughly and
apply some dielectric grease. Even if they look clean, don't assume
they are. I even had to replace my negative ground connector on the
battery cable. It looked perfect from the outside but was dirty and
out of round enough that it wasn't getting a consistantly good
connection. My cranking power doubled when I replaced it.
Resistor Wire
The resistor mentioned above is
actually a nichrome (sp?) resistance wire; Mopar uses a conventional sand
resistor, and I don't remember what dorF uses. I've also fixed a few which
would start only when the key was *released* from the start position.
You either have a porcelin ballast resistor or a resistor wire: a ballast
resistor is hard to miss. It looks like a small rectangular box and is
porcelin; a resistor wire is almost always covered with a woven material and
is usually silver.
In a point system you can tell if you have a resistor or not by connecting
a volt meter to the plus side of the coil and to the negative battery post,
make sure the points are closed, iginition key should be turned to run
position, if you have 6 volts there is a resistor present.
HEI Feed
The best way to find power for your HEI (at least it's how I've done it
on 20 or so conversions) is to take it from the fuse panel. Get out your
test light and find one of the spare terminals which lights the test light
in both run (ignition key in "run" position) *AND* start (key in start
position). Hook a wire from here to the HEI's "BAT" terminal and you're
set to go.
There was an empty receptor in the fuse panel marked "IGN" on my 69. By
plugging into this, I was able to eliminate the wire from the starter. Just
a guess, but I would assume the resistor wire gets (+) voltage only in the
run position. If it got both, there probably wouldn't be a need for the "S"
wire on the starter.
The 12 volt source has to be hot when the ignition is on, but it
must also be 12v at the start position (while cranking). I finally
ended up finding the IGN. position on my fuse panel and using that. If
your lettering is worn off the panel, try tracing back the old
resistance wire that want to the positive coil terminal on your old
setup. You can check the
fuse panel with a test light if you don't have a spot clearly marked.
If that doesn't work, there is a diagram in the chassis manual,
that shows the fuse panel and all the connection locations. You could
also run a second wire from the "R" terminal on the starter and you
will be sure you have 12V for cranking. You would just splice the two
together.
I ran a #14 wire from the fuse box on the ign terminal through the hole on
the firewall where the A/C wiring harness goes through. Nice and clean
because the hole is right behind the distributor.
There is a power window terminal on the fuse block.
This supplied power to a relay, through the ignition switch.
The main feed for the window motors came from the horn
relay/junction block, through a 30 amp circuit breaker, and
then to one side of the relay. When the key was turned to the
"on" position, the relay was pulled in, completing the circuit.
One wire from the ignition switch to the BAT connection on the HEI unit.
Keep in mind, if you are replacing an original points unit, the wire,
purple I think, from the fire wall to coil, is a resistor wire. This is
to lower the voltage to the coil. You need to replace this wire with a
regular non resistor wire.
I went to the junk yard and pulled the entire wiring harness from the
fire wall from a donor 71. I then pressed the spade connector out of
the molding then did the same with my molding and pushed in the non
resistor wire.
I know I'm not being clear but just make sure the wire connected to your
distributor is not a resistor wire or you will not get as strong a
spark.
You can run your twelve volt wire right off the iginition switch or
splice on to a wire going into the fuse panel, but not directly to a fuse;
because this wire will get hot.
Start the Car and Set the Timing:
Check cleanences with the firewall. The advance unit should not be right up against
the firewall. Try about 1" or so in order to initially fire the engine. You
will set the timing more accurately once the engine is running.
Start the engine. You may have to retard (move distributor counter-clockwise) or
advance (move distributor clockwise) to get the engine to start. Once running,
make sure you disconnect and plug any vacuum advance on the distributor, to set
you initial timing. Of course you want to reconnect the vacuum advance later.
See the Tuning section for timing details.
Recommended Might-as-wells:
See the Conversion Recommendations section.
[ Thanks to Bob Valentine, Mick Gillespie, Bruce Roe, Thomas Smith
Mike Schlottman
for this information. ]
Conversion Testing
The first thing to check on your HEI conversion is the 12V source. The
point distributor had a series ballast resistor somewhere, which is shorted out
when starting. Sometimes its just a special high resistance wire between the
ignition switch and the coil. This resistor must be shorted out for an HEI
distributor. A test for this is connecting a wire directly between the HEI
input and the battery (alternator stud is good); if the problem stops you need
to fix your IGN wiring. Of course you will need to pull the wire to stop the
engine.
If you are not sure you have voltage while cranking you can run a wire
from the starter solenoid (R terminal) into the wire you are using for your
twelve volt source.
Any ballast resistor circuits will have to be eliminated. The HEI needs
pure 12V.
I've done two conversions to HEI for my 66 big cars. Once you get 'em
running they're truly better than points. I'd go get a known good module
(i.e. new) and known good coil (i.e. new) and substitute them for your
boneyard parts.
These have been critical to the functionality of my HEI's. In one case my
coil went bad and the car stopped dead. Dead. With the module there's really
no alternative to replacing it since it is electronic.
Be sure that once the car is running that you've got a full 12 volts to the
BAT terminal on the HEI. I think you're right that you need to remove the
ballast resistor, not put one on.
If you pull the HEI back out of the car, you might check for distributor
sloppiness. Like lots of up/down travel of the shaft, or the ability to move
the shaft around inside it's housing.
Be aware that I rewired the switched BAT lead with thick (~10gauge) red wire
in place of the original distributor lead. This neatly removed the ballast
resistor and insured minimal resistance between the ignition switch and the
HEI unit.
The only dumb (or supposedly so) thing I did was to also run the electric
choke wire off that big 10 guage lead as well. I've not had problems but some
listers feel very strongly about not doing this.
[ Thanks to Chris Fair
for this information. ]
HEI Trouble Shooting
Coil:
Clean it up and look at the clear epoxy for signs of arcing to ground.
___________
| | (View of an upside down HEI coil)
| _ |
| /A\ | A - coil secondary output terminal (where the
| \_/ | carbon brush spring makes contact)
| | B - RED wire (BATT terminal connects here)
|_________| C - BLACK ground (held down by a coil mounting screw)
| | | D - YELLOW (or WHITE) wire (TACH terminal)
| | |
B C D
| Using this chart, make the following Ohm Meter tests.
Any failing test means replacing the coil. |
| | Probe Points | Expected Results |
| | B-D | about 1.6 ohms |
| | A-C | 8.1-8.2 kiloohms |
| | B-C & C-D | > 1.2 megaohms, but not infinite |
| | A-B & A-D | infinite |
Check if the ground strap is in the coil. A broken or loose strap will arc,
making a sound like the advance weights clicking against the side of the cap.
Some new kits don't come with this strap and many forget to put it on.
GM HEI (internal coil) 1974-1975 6k-30k ohms secondary
GM HEI (internal coil) 1976-1979 Infinity
GM HEI (internal coil) 1980- (see text)
The resistance between the primary terminals of the coil should be
no more than 1.0 ohms. The resistance between the secondary output
terminal and the primary should be between 6k and 30k ohms. Integral
coils on applications later than 1975 should have infinte ohms between
the secondary and the primary. However, 1980 and later applications
should be replaced if there is infinte ohms between both the
primary and tach lead. This is also true of applications later
than 1980 with an externally mounted coil.
Q: My question is why measure for DC resistance between one lead of the
secondary and a lead of the primary anyway? Shouldn't this always
be infinte?
It would for what you might think of as a regular transformer but the
coil is an "autotransformer" -- no pun intended. It's like a transformer
with a centertap and no secondary. The "primary" would be from the
centertap to one side. The "secondary" across both sides like so:
Secondary -> ----)
| )
| )
| Primary ----)
| | )
| | )
|--> |--> ----)
So the primary and the seconday windings aren't electrically isolated
from each other.
| Module: |
C B G W
__ __ __ __
\_\_ \_\ /_/__/_/
\ \___________/ /
\ /
\ (G) ( ) /
\___________________/
|
|
Modules
I've seen have the terminals labeled. This may help if yours isn't. The
(G) is the ground terminal, and it is one of the holes that the screw runs
through to attach the module to the distributor.
|
-
Remove the module from the distributor. (watch out for that nasty
dielectric grease on the underside, It's relatively hamless, but goopy)
Connect a test lamp between the B and C module terminals and jumper +12
volts to the B terminal and then ground the module at the (G) terminal. If
the lamp lights then the module is bad.
-
If the module passes step one, then jumper between the B and G terminals.
The lamp will light if the module is ok.
If you suspect the module at this point, you might as well take it with you
to the parts store if they'll test it for you, and confirm your diagnosis
before you buy a new one.
Pickup Coil:
-
Remove the pickup coil leads (carefully) from the module. Connect the
ohmmeter to the base of the distributor and the pickup coil lead. The book
doesn't specify which one, so I assume either one will do. Personally, I
checked both. Operate the vacuum advance through it's full range. (I didn't
have my vacuum pump with me so I sucked on the vacuum line going to the
advance. If you use that method you're likely to spend the rest of the day
spitting. I don't reccomend it, but it'll do in a pinch.) The meter should
read infinite in all positions.
-
Connect the ohmmeter between the leads coming from the pickup coil and
operate the vacuum advance through it's full range with a vacuum pump.
The meter should read 650 to 850 ohms in all advance positions.
Conversion Results
Took about 2 hours (took a half hour just to get the old one
out!) to replace it, make the plug wires and set the timing.
Went done the road to do a burnout, what a difference! Before I could
lay rubber until about 30mph and get a good 1-2 second chirp when I
shifted into 2nd. Now it layed rubber to 60mph! The car runs smoother,
takes off better and really runs like a bat out of hell when I punch
at 80mph. Take my advice, get an HEI.
I did NOT have to dent my aircleaner. The Accel super coil has a
lip that extends over the plug wire on the distributor that was in the
way. I simply pulled out the Dremel, cut it off and the OAI airclener
base just fits.
The conversion to HEI is complete and the car has never run better. It
feels like I have 455 in there ;-). I highly recommend this conversion
to anyone who is still running points.
Starting, hot, or cold is instantaneous and it runs through the gears
(took it up to 5000 rpm max.) like a true muscle car ;-). I foresee
better gas mileage too, as a lot less throttle seems to be needed to
get up to cruising speed.
[ Thanks to Mick Gillespie
for this information. ]
Post Conversion Recommendations
Air Cleaner:
Get the air cleaner assembly from an HEI engine as well, as the original
air cleaner will hit the HEI distributor cap.
There may be some air cleaner clearance
problems; the HEI engines tended to use an air cleaner shifted forward instead
of centered around the carb.
You might want to massage the original cleaner housing, but there is a sort of more
elegant solution. A trimmed tomato juice can is used to space the air cleaner
up about a 1". Spacers and adapters are frequently included in aftermarket
one-fits-all chrome aircleaner. But a Rochester 4V has a smaller ring diameter.
This solution is pretty clever, and the basic approach applies to all carbs/air cleaner housings.
Coil and Module:
The HEI should work fine for street motors, and if you're concerned about
getting a hotter spark, you can replace the stock coil w/an aftermarket one
for reasonable money. Of course, if you like the RPM limiter (don't need for
an auto trans unless you manual shift, of course), then spring for the
aftermarket types.
Be careful of the type of rev limiter used with an HEI and other electronic
ignitions since some styles can damage them. If I want that capability, I'd
probably get an MSD 6A-L or equivalent.
Electronically Regulated Alternator:
You must convert to a electronically regulated (non-vibrating regulator)
alternator. Converting externally regulated GM alternators (pre 1971) to
internally regulated post-71 alternators is a relativly easy affair.
You will be burning out HEI modules at record pace if this is not done!
I took a look at the mechanical regulator and I could see how it would give
my HEI a hard time, causing it to fail shorty after installation. One set
of points in the regulator is
eaten up pretty bad, and it turns out the regulator was causing some
problems with dim lights, and what appeared to be generally low battery
voltage. When I started the car after installing the new regulator the
ammeter indicated about a 25 amp charge. The mechanical regulator was not
correctly sensing the battery's charge.
My '71 had the mechanical regulator stock from the factory. However, my
Olds Service Manual indicates some cars of that year had the solid-state
regulators in the alternator. To check, if you see a black box above the
distributor about 3" square on the firewall you likely have a mechanical
regulator. I say, "likely," because some replacement, aftermarket
regulators are made now that install in the same location and look the
similar but have solid-state, electronic guts.
To confirm whether or not you have a mechanical regulator or an electronic
replacement, disconnect the battery negative cable (this will ensure you
don't short out and destroy the regulator in the event it is electronic).
Take off the regulator cover. If you see what looks like thin metal blades
with contact points on them, you have a mechanical regulator. You may also
see a little plastic adjustment knob.
Now, to eliminate any question, look at the plug going into the alternator.
If it is about 1/2 inch square, you have an externally regulated alternator.
If the connector is flat, about 1/4 inch wide by 1 inch long, you have a
solid-state alternator EVEN IF you appear to have an external regulator on
the firewall. The reason I say this is that there is this nifty procedure
in the FAQ that tells how to convert to an internally-regulated, solid state
alternator and disable and jumper the original regulator. This allows you
to keep the regulator on the firewall for a nearly stock look.
My point is, if the alternator has the externally-regulated style plug (the
square one) it may still have electronic regulation if the regulator has
been replaced. BUT, if you have what looks like the internally-regulated
style plug (the flat one) you definitely have an internal, electronically
regulated alternator, even if you have a regulator box on the firewall.
You'll have to check and see what you've got. BTW, if you have the older,
externally regulated alternator, BUT have an electronic replacement
regulator, the FAQ indicates you don't need to change alternators to go to
HEI.
Setting Initial and Vacuum Advance:
Please note that HEI's are curved way different than the pre-emissions points distributors.
There are kits to handle the weights/springs for the mechanical advance
available at most stores. For an auto
tranny you would like to have total mechanical advance in by about 2500 rpm.
You check this with a timing light and tach. See the Tuning section.
Getting your HEI checked out and recurved against the old unit will work; doing
it yourself is cheaper. For vacuum I use a hand vac pump gauge. With the vac
canister out observe how much vacuum is needed to start it moving, and how much
vacuum at maximum advance. And with a 6" dial caliper, how many thousands total
movement?. Mine show about .300" movement, which translates to 24° on
the engine. If your HEI vac unit is a bad match, get an adjustable one. This
can be set for total travel, and advance starting point. If these match on the
bench, they should match on the engine
I set mechanical advance on the engine. First make sure your timing chain is
reasonably tight (you DID replace it, didn't you?). See how many degrees you can
rock the crank back and forth before the rotor moves. More than a couple degrees
is bad. Put a tachometer on to see RPM. Disconnect vacuum advance to avoid
confusion, and temporarily move up timing so engine runs OK. While slowly
speeding up engine, observe RPM where first starts (use a timing light, we are
just looking for change, not absolute timing). Observe RPM and amount of advance
at several points up to maximum advance. With these measurements on the original
distributor, do the same on the HEI. Change springs or weights as Fred said till
the HEI is close to the original. You can use the same method to check the vacuum
advance by keeping engine speed below where mechanical advance starts, and use the
hand vacuum pump while obseving advance
Once the two units match, connect vacuum and set timing to spec. Trying it also
a couple degrees either way is probably worth the test.
Then it comes down to getting the right mechanical and vacuum
advance curves. Weight kits and adjustable vacuum canisters are available for
the HEI. You can curve out your old and new units on your engine if a
distributor machine is not available. With vacuum disconnected, note initial
timing mark reading at idle, and change as RPM is increased to max. Possibly
you will need to temporarily advance the distributor position (rotation) while
testing to get the engine to run over the range without vacuum. Next measure
vacuum advance using a vacuum hand pump. This must be done over a low RPM
range where mechanical advance has not cut in, or bind the weights. This can
also be done on the bench using a micrometer directly on the vacuum canister. If
the advance arm is the same length, the movement of the vacuum activator should
be the same. Set the screw to the point where advance just begins, and a cam
is set to limit maximum advance
See the Tuning section for more details.
![[ Notice: ]](hand_rig.gif)
Please refer to the
Tuning
to optimally setup (timing, advance, etc) your HEI converted ignition.
Please refer to the
Ext. Regulated to Int. Regulated Alternator Conversion
section as well!
HEI Conversion Experiences
The major benefits I have seen are in easier starting and smoother
performance. I don't think my gas mileage improved though, since I switched
to a 4 barrel carb and a bigger cam at the same time; not to mention the big
valves :-). I have revved it out to 6000 RPM once and it was still pulling
strong.
The recurve kit did help performance noticeably, but after a lot of trial
and error, I ended up using only one "medium" spring from the kit.
Seriously, I like the HEI and electronicly regulated alternator much better.
The reliability factor is a whole lot better in my opinion too.
It's still an expensive proposition though, to switch out parts in perfectly
good working condition and replace them with new ones.
The only difficulty I remember, is forgetting that I needed my 12v source to
be available in both the ignition "on" and "run" positions. The distributor
fought back a bit getting it out, but a bit of wiggling and banging, and out
it came.
I also added a spacer under my stock air cleaner for better clearance.
I've done the HEI swap, about a year ago. Any fuel economy benefits are
negligible, compared to a well tuned points system. However, the
improvement in smoothness is stunning, starting is easier, quicker, low end
pull seems to be stronger. Easy swap to do, well worth it.
If the points don't really bother you then you it may not really be worth
your while to do the swap. You ~may~ pick up a few mpg since you
can run a larger gap on your plugs. I say may because it all depends
on what your exact combination is and what other mods you make
to take advantage of the HEI. You can usually richen up the carb some
so that any given rpm you have to depress the throttle less to get the
same amount of power, but as I said, it all depends on the whole
combo. Rock solid reliability is the main cause of many making the
switch since with an old car anything that gives you one less thing to
worry about is usually worth it. If you think about the fact that the
performance of points (effieciency) constantly degrades from the time
you put them in and the HEI stays constant then that's something you have
to consider.
[ Thanks to Mick Gillespie, Todd Morris, Mike Bloomer
for this information. ]
[ Thanks to Chris Witt, Fernando Proietto, Pat Clark, Andrew Green,
Bob Handren, Tom Lentz, Greg Pruett, Bob Barry, Joe Padavano, Graham Stewart,
Scott Kozhill, Scott Mullen, Kevin Wong, Chris Fair, Erik Nowacki,
Chris Ruper, Mark Prince, Rich Inacker, Todd Morris, Kurt Heinrich,
Jeff Easton, Mike Frederick, Dorian Yeager
for this information ]
Tuning
Advance Curve / Recurving
Introduction:
You have an "initial" timing setting for idle and as the RPM's go up, the
weights inside the distributor overcome the force of the springs preventing
the weights from moving, due to centrifugal force. As these weights extent outward
the timing advances, until they hit their stops. This is called mechanical advance.
Between your initial and total mechanical settings, you have the advance curve or
specific amount of timing at a certain RPM. If you plotted this on
a graph it would look like a curve that starts adding just a little advance
at first and more towards the total end. Vacuum advance can add a bit more timing
advance over this curve. You need an adjustable timing
light to really play with it, or a degreed balancer so you can watch the
curve happen as you raise the rpm. By swapping in lighter or heavier
wieghts and stronger and weaker springs, you can manipulate this curve
in several different ways, but it is sort of a black art, and takes a bit of
talent to get the most out of it.
The recurve is easy enough to do yourself, but a lot of trial and error is
involved. You need a graduated timing light as mentioned (or timing Tape). I
used the Moroso kit which is cheap and has lighter weights and two weights
of spring. With your stock springs that makes three different weights of
spring. You can calculate all the combinations and permatations. After a lot
of messing around with varying combos, I ended up using both stock weights
and a light spring on one side and the stock one on the other side. I also
used a bushing that came with the kit to limit the amount of vacuum advance.
Ended up with 34° total timing, all in by 2500 RPM. this is on a 69
350/350 with Edelbrock Total Power pkg. (heads excepted). I was originally
after 36 deg at 2500 RPM and the car ran like a raped ape at mid to high
RPM, but I couldn't get rid of a real rough idle and it would baff out
starting off at light throttle. set it back to 34 deg. and it runs a lot
smoother but I think I lost some performance.
It takes a lot of patience (or luck), to get the curve where your car wants
it.
If you plot the amount of centrifugal advance vs. rpm, you get a
"curve" that is usually linear up to a maximum amount of advance. Different
springs will adjust how soon that curve begins from the initial advance, as
well as how long it takes to get to maximum advance. You can also include
the vacuum advance in that curve, but because that advance is proportionate
to engine vacuum, it's extremely variable, and usually not counted in what's
referred to as the distributor "curve".
Recurving or setting the advance curve involves springs, and in extreme
situations, new weights (either heavier or lighter)
and limits or extensions to the slots or pins that regulate maximum advance.
Springs and weights are included in a recurve kit.
You can do it by machine, where you match the amount of advance at certain
rpms to some ideal curve. Or, you can do it yourself in about an hour's
worth of testing, and create a custom curve that's ideal for your particular
engine. There are many advance kits out there; I was happy with the Crane
adjustable vacuum advance kit, which cost me $22.
The existing distributor curve may be ideal for your engine, or it may
not. Usually, you want to have as much advance as you can, before detonation
(spark knock) sets in. You want to find out how much total advance you can
run, and try to get that much advance in there as soon as possible. The
exact numbers are not all that important, which is why curving a distributor
on a machine may or may not improve your car's performance, since the ideal
curve that the distributor is set to on that may not be the ideal curve for
your car. It's not just the cam that affects the ideal curve, but also
gearing, transmission, engine condition and other modifications, jetting,
fuel quality, driving style, atmospheric conditions, etc.
I'd recommend something like the Crane kit; follow its instructions, and
you'll likely be happier with how the engine runs afterwards.
The various combinations of springs and wieghts available will determine
the speed and rate of change of the mechanical advance. This is not
a linear change (ie, a straight line if you graph it rpm by advance) but
has a more rapid rate of change at either the lower or upper part of the
RPM band. This is your curve. What is important is not to set the curve
to exact specs but to what the engine wants. Because of this, you will
eventually have to play with it on the car to get it exact. Variations in
your combination (carb, cam, CR, ignition, etc) will make the optimal
curve different for just about every engine. One curve may work from
one engine to the next but still not be optimal. The adjustable vacuum
advance comes after the distributor curve for fuel economy and drivability
reasons. All you really need to curve a distributor is a fundamental
understanding of how the advance operates, an adjustible timing light,
an accurate tach, a curve kit with various springs and wieghts, and lots
of patience. Most of the good curve kits come with instructions which
will set you in the right direction. As long as you don't enter the
detonation
range just getting the curve close should be enough, since driving around
town you really won't notice a difference of a few degrees here or there.
If you were seriously drag racing however, you might find a few tenths.
Hope this helps and wasn't too confusing.
A friend has a Sun distributor machine he picked up at an auction. Dates
from the 1950s but everything works and it has all the documentation. It
is quite a thing to see. It has a vacuum pump for the vac advance it
drives the distributor with an electric motor. It has all sorts of dials
to measure different parameters as it spins the distributor. I can tell
you from watching it that you wouldn't want one of those advance weights
to ever come loose at speed... it would be quite a violent collision with
whatever it hit. A distributor really spins a lot!
He did mine last year. With a service manual for the specs you want it
actually is pretty straightforward to check. With the machine you can see
how the different weights will affect how much advance kicks in at a given
RPM. Similarly with the vac advance. Also you can see how any variance or
wobble in the bushings affects advance or dwell. Neat. I wonder how many
of these machines are still in shops?
Race engines don't need vacuum advance, because they're never at part-throttle
anyway. Any street engine spends more time at part-throttle than WOT, and can
always benefit from having vacuum advance. Magazines like Hot Rod test engines
at WOT (Wide Open Throttle) on a dyno, where vacuum advance plays no role, so
they leave it off the engines. Then they tell you that you need 36 deg, or 32
deg, or whatever, of mechanical advance. They totally fail to inform you that
your engine will run better on the street with additional vacuum advance over
and beyond that 36° or whatever.
[ Thanks to Mick Gillespie, Robert Barry, Mike Bloomer, Greg Beaulieu,
others below for this information. ]
Factory Setup and Information:
Delco produces a specification book called the "1.2" manual. The good
news is that all distributor advance curves are listed. The bad news is
that they are listed by distributor part number. You cannot just look
up the curve for a "70 Toro". Fortunately the number is stamped into
the distributor housing.
The centrifugal mechanism is subject to wear, which
alters the curve. This is common on all distributors. The weights will
cut into the pivot pins, sometimes shearing them off! The proper fix is
to buy a new distributor mainshaft from GM. The last one I got was $60,
had a "performance" curve built in, and fit a Che*y. Incidentally, that
mainshaft "fixed" a number of "carburation" problems! There are repair
kits to salvage the worn pins in the original mainshaft, they are a pain
in the tuckus if you don't have a torch to heat the weights cherry red
before trying to drill the pivot holes oversize. HEI's are especially
bad for having worn centrifugal mechanisms because there was no need to
remove the cap and rotor to replace points. No mechanic on commission
is going to rip off the cap and rotor to lube the advance mechanism out
of the goodness of his heart. Point style distributors needed the cap
pulled off to replace the ponts, and so sometimes the advance was lubed
at the same time.
The distributor bushings especially on points style distributors also
wear, altering the timing in erratic ways.
Virtually all distributors from GM have WAYYYYYY too much end play, and
should be shimmed so that end play is around .008-.015. This prevents
dynamic timing changes due to the distributor gear jumping up and down
on the cam gear. Since they are helical gears, vertical movement of the
distributor gear causes the shaft to rotate, changing the timing.
[ Thanks to Schurkey Swanke, others below
for this information. ]
Overall Advance Curve Information:
This discussion applies to points ignition or any distributor type
ignition system. In any case, take this discussion as a guide, not written
in stone. Every ignition systen will take some trial and error for
maxiumu performance.
So much depends upon the characteristics of the motor,
vehicle weight, axle ratio, etc., that no one setup is exactly the same,
but the more info on all that stuff, the better. If you're getting part
throttle ping, but are otherwise happy with the timing curve, you can
always go to an adjustable vacuum canister and fiddle with that until you
dial it out.
Please note that HEI's are curved way different than the pre-emissions points distributors.
There are kits to handle the weights/springs for the mechanical advance
available at most stores. For an auto
tranny you would like to have total mechanical advance in by about 2500 rpm.
You check this with a timing light and tach.
I'd suggest buying an advance kit with new weights and various
springs so you can recurve the distributor. The factory
HEI mechanical advance is very
s-l-o-w, and the vacuum advance is way too much. Adjustable vacuum advance
pots are available, or braze the slot to limit advance to about 10.
What you want to do is have similar advance specs to that of the points
distributor. Full mechanical advance at 2000-2500 is ok for an automatic
transmission. A standard transmission
requires quicker advance, so it's full about 1500. Again, vacuum should be
limited to no more than 15°.
The total amount of advance or overall advance depends on many things (compression ratio,
head design, rear-end ratio,
weight of your car, etc) but I've been told numbers of around 10° to 15°
advance at idle, around 36° full mechanical advance (with
the vacuum advance disconnected). At part throttle, high rpm, with vacuum
advance, the ignition timing should be somewhere in the range of 50°.
That number surprises many, but that's what's needed for maximum
fuel economy at part throttle (cruising).
Total/overall advance is calculated as:
[total @ RPM @ inHG] = [initial] + [centrifugal @ RPM] +
[vacuum @ inHg]
Centrifigal and mechanical advance mean / are the same
adjustment / measurement.
Total advance at high rpm and wide open throttle = initial timing +
mechanical advance
Total advance at high rpm and part-throttle = initial timing + mechanical
advance + vacuum advance
One rule supercedes everything else: if the engine detonates, reduce the
timing immediately till all traces of detonation are gone. Detonation will
kill your engine in a very short time (it breaks piston rings, crumbles
pistons, etc.).
The best way to set ignition
timing is to modify the initial advance and advance curve to get the best power
at WOT at all rpms. Do this with the vacuum advance disconnected. Once the
mechanical advance is dialed in, connect the vacuum advance, and dial it in for
best *part-throttle* power with no pinging or surging. This last step is
universally omitted when the car magazines write about engine buildups.
There are two methods to setting and determining timing. One says be
concerned about initial timing, the other says be concerned about
overall timing. You should probably be concerned about both, letting
neither negatively affect the other.
Try as I might, I cannot understand why an ignition kit would include
"lighter springs and weights". The purpose of the the weights is to advance
the timing as a result of the moment and rate they move due to centrifical
force (the rotation of the distributor shaft). To change the point at which
they begin to move and the rate of movement to their maximum swing is the
function of the springs. The lighter the springs, the sooner and faster the
weights swing to maximum (the earliest max advance)......the heavier the
weights, the same result. To answer your question, to obtain the earliest
movement and most rapid swing to maximum advance would entail either lighter
springs or heavier weights; but not a combination of light/light or
heavy/heavy.
I would say go with what Crane recommends.
When curving the distributor the best way to go is to use the stock wieghts
as a baseline. Go heavier on the springs to raise the rpm where you
get total advance, lighter to lower it. A good curve kit will have an
assortment of springs. For the wieghts, the opposite is true in that the
heaver the weight the lower rpm for total and lighter to raise it. Keep
in mind your initial and total timing points are only part of your curve.
It's also how it gets there. Light springs will give a quicker jump off
initial and level off near total. Heavy springs will give a more gradual
advance off initial and be more rapid the closer it gets to total. That's
why they call it a curve.
A good
starting point is to use one light spring and one medium spring. You want
total timing of 34-36° BTDC at 1500 to 1800 rpms.
Initial timing will probably be at 14 to 18°.
I use full mechanical advance and no vaccum advance. I also put a stopper
in the distributor in order to not let the timing go beyond 36° total.
A good rule of thumb for a street/strip combo is about 14-18° BTDC
initial advance to approx. 35° at 3000 RPM maximum advance
The possible combinations of weights, springs, quantity and rate of
advance do seem to make the task of determining timing to be fairly
complex, very much like a trial and error operation. The ideal
combination is quite dependant on compression, rear gear, intended use,
cam, economy vs. performance priorities, etc. It is difficult to simply
take a recommendation from a friend as to the correct settings, since that
may not apply to your car.
While all this is true, it shouldn't be that hard. While a distributor
machine makes it a piece of cake, one of the timing lights that give
you timing advance values at each step works just as well. After all,
your engine can do anything the distributor machine can.
What can also get confusing is that some of the advance curve
kits recommend removing or replacing the sleeve over the pin in the
mechanical advance mechanism. This makes using the original initial timing
value a potential problem. A slightly different approach has worked for me.
You are correct that you should have full advance at 1500 dist. rpm which is
3000 engine rpm. Most of the 1966-72 Olds V-8 were factory set to have full
advance in as soon as 3000 up to 4200 engine rpm.
Note:
| Application | Engine RPM | Distributor |
|---|
| 68 Toro/442 455 4 bbl | 3000 | #1111289/1111292 |
| 68 non-Toro 455 4 bbl | 3600 | #1111469 |
| 68 455 2 bbl (in what?) | 4000 | #1111288 |
| all 66-67 425's | 4000-4100 |
Plus other specs I have show other years are basically the same as these
listings.
A 2.56:1 rear is a pretty darn stiff rear ratio, which means the engine
sees a much bigger load (less torque multiplication through the rear gear).
A bigger engine load means increased cylinder pressure and increased
tendency to detonate. Translation: be cautious in going to lighter and
lighter distributor springs, as your engine is working harder than most due
to the very stiff rear end. Again what I've heard for Mopars is to use full
advance by roughly 2500 - 3000 rpm.
If you can get away with full advance
at lower rpm with no pinging, fine. Just be very careful not to run into
even mild "silent detonation" which can still break piston rings and damage
pistons without being loud enough for you to hear over the sound of the
car. Once you find the point where the thing pings, back off a few degrees
to give it a safety margin. Also a hotter day or a tank of bad gas might
come your way and needs a safety cushion. Better an engine a few % down on
torque than one that needs a rebuild due to detonation.
[ Thanks to Donny Arnold, others below
for this information. ]
Initial Timing:
The general rule is to run as much intial advance as you
can, (without making starting impossible), and make full throttle runs
with various spring rates, (you can mix springs without hurting anything
and actually advance the curve in steps). This should be done with no
vacuum advance hooked up at all. Once your best performance is dialed
in with no pinging, then go ahead and hook up your adjustable
canister.
On the initial advance, assuming you still have decent compression, if the
motor turns over after slight hesitation, (starter load), you're
probably running at least 12° of initial advance. If not, it's
probably something less.
[ Thanks to others below
for this information. ]
Overall Timing:
For some reason a lot of people seem concerned about initial timing. It
has virtually nothing to do with performance. The measurement you
should focus on is total timing advance and the advance curve. You want
as much advance as you can get, coming in at the lowest RPM possible
without detonation. Put a timing tape on your harmonic balancer.
Unplug the vacuum advance from the manifold vacuum and try various
distributor springs to get your mechanical advance started around 1500
rpm and all in by 3000 rpm or so. One of those engine analyzers with a
tach in it is crucial here to map out the amount of advance at a given
RPM. Also, rev the motor right to 5500 rpm to check for timing scatter.
Don't set your timing with initial advance only. This tells you nothing
about the total advance which is near or where the advance is while the
engine is running at speed. This value only has meaning for a totally stock
ignition system.
Disconnect the _vacuum_ advance and rev the engine up slowly while using a
timing light. Measurer the total advance. This should usually not be more
than 35-36°. Yes, your harmonic balancer isn't marked that high - so
mark it. Measure the distance on the timing tab and add to the balancer
marks already there. No, it won't be exact but is close enough for a start.
Better way is to get a timing tape for the balancer from Mondello
(expensive) or PAW (less expensive) or anywhere else that has one. They are
made for Olds engines. The generic tape will be for a Chevy balancer.
Distributor curve with 12 deg initial advance
| | RPM | Cent. Adv. | Total Adv. (no vac) |
| | 1000 | 2° | 14° |
| | 1600 | 10° | 22° |
| | 2300 | 15° | 27° |
| | 2700 | 20° | 32° |
| | 3000 | 24° | 36° |
| |
| | Which looks like a pretty reasonable curve
for premium gas and a CR around 9-9.5:1. |
| |
| |
Total advance is the sum of
-
Static advance- the timing you set at low speed with vac line disco'd.
Does not vary once set. Ideally.
-
Mechanical advance- usually kicks in above 1500 R's or so. Varies with
RPM only- not load on motor, etc.
-
Vacuum advance- usually kicks in strongest just above idle, tapers off
gradually to none at WOT. Depends on throttle position and load on the
engine.
Total advance ought to be between 32° to 36° for most any non-emissions
performance engine. As far as I know most stock HEI's produce over 40°. Get
an adjustable vacuum advance from Crane (comes with an advance limiter).
This kit also comes with springs to adjust the centrifugal advance. I have
not found it necessary to change the stock weights to the aftermarket weights
the Mr. Gasket, etc. kits come with although maybe you might want to try
it to see if it helps your particular combo. It should work without problems
with stock weights though.
It is important to check the top end (5000-6000 rpm) for timing
fluctuations, as it is a good indicator of a worn/loose distributor. By
using one of the timing lights with the adjustable dial on the back, you
are only simulating the revs. Put a timing tape on the balancer ($10
from Summit) and rev the motor for real!
Make sure you are using the octane gas that you normally will run, and
that you are testing on a day with average weather. Setting the timing
on a 95° day will result in too mild of a curve, just as setting it
on a 50° fall day will be too aggressive for summer driving. Intake
air temperature and fuel octane have significant effects on detonation.
Cooler air/higher octane fuel let you set a more agressive timing curve.
That's why the W-30 had OAI and a recurved distributor. You can then
road test the car (with the vacuum advance disconnected) to find
detonation at various rpms. Go back and try different
spring/distributor cam/weight combinations to alter the curve to
eliminate detonation spots. By drawing a curve on a graph (using the
total advance measured at various rpms using your timing light and the
timing tape) you can compare this curve with your observed detonation
points and then reshape the curve with different springs/weights/
distributor cams to arrive at the desirable setting.
The first place I would suggest starting is with the specs Olds established
for your engine in the first place. They can be found in a Motor manual
covering the year of your car. Interestingly, my GM service manuals (for my
cars anyway) don't give these values but Motor's does. Using a timing light
you can set up the distrubutor advance characterisitics to match those of the
original points distributor. But those values are the compromise
settings given mass production tolerances, etc.
The other way is to match your distributor to your engines requirements. I
usually don't pay much attention to initial advance at the beginning of this
exercise because what you're looking for is actually the total advance,
initial + mechanical + vacuum.
In-the-ballpark numbers are about 35 degress total initial and mechanical
advance and limitation of vacuum advance to about 10-15°. Most of the
HEI's I've played with have 20°+ of vacuum advance. Too much.
Disconnect the vacuum from the advance pot. Using a timing light with
advance measurement capability, check and set the total initial + mechanical
advance. You'd like the mechanical advance to be fully in by ~1500 to ~2500
rpm and be about ~35° total (without vacuum). Set the distributor at
this total advance position. Depending on auto vs. manual, compression
ratio, cam, etc. you may need a little less. I've found that an Olds engine
usually doesn't like initial + mechanical (centrifugal) of more than 36°.
Since this early advance (compared to stock) usually means lighter springs
than stock, the inital timing value is many times much different from
published "tune-up" values and therefore pretty much irrelevent. My neighbor
with a 66 GTO went bonkers trying to make the two agree (initial and
mechanical) for a Mallory unit he was installing until I pointed this out.
Took about 5 minutes after that.
When you have your mechanical advance curve set up, install a Crane
adjustable vacuum advance and follow their instructions for setting it
to eliminate part throttle opening detonation. I highly recommend this
part. The next time someone asks you your initial timing setting, tell
them you don't know/don't care, because you will have spent your effort
where it counts, namely in setting the total advance and the advance
curve. By using a stock GM HEI distributor, you are ensured a ready
supply of cheap (usually free) parts and performance that is more than
adequate for the serious street car. Have fun, wear safety glasses when
revving the motor (in case of broken belts and the dirt flying around at
5500 rpm) and keep your fingers out of belts/fan blades.
[ Thanks to others below
for this information. ]
Centrifugal (mechanical) Advance:
The centrifugal advance weights should be recurved to use with your
older car that expects more timing. You can get a recurve kit at most speed
shops for a few bucks that fits all HEI distributors. When installing it
remember that Old's spin counterclockwise and it's a 99% sure thing that
the instructions show a clockwise spinning Chevy, so reverse the weights.
The kit consists of different weights along with a bushing to limit the
total advance (if that's what you want), and a few different strengths of
springs.
Remember that the advance weight set up is for a smog controlled car. Your
car will work with the original setup, but it will feel a little sluggish.
Buy the Accel re-curve kit. You will notice a big difference.
When putting the re-curve you will need to re-set the initial timing as
the lighter springs will cause the timing to become more advanced. You
will hear pinging. So keep that in mind. When using the re-curve
kits, use the lighter springs, not the weights. You only get one pair of
weights and 3 pairs of springs in varying degrees of stiffness. If you
use the lighter ones first (springs), re-adjust your timing.
I dug out my info on the factory HEI weights/cam set-ups that will give
you more mechanical advance than normal. They are found in the following cars:
| Engine | Car | Deg. Mech. Adv. |
| Olds 260 V-8 | 1975 Pontiac Ventura
1976 Pontiac Ventura
| 28°
26° |
| Olds 260 V-8 | 1975 Olds Cutlass, Buick Apollo/Skylark
1976 Olds Cutlass, Buick Apollo/Skylark
1977 Olds Cutlass, Buick Apollo/Skylark
| 28°
26, 28°
26° |
Remember, you don't need the whole distributor, just the center cam and
the advance weights. I'm using #139 weights and #410 (I think)
distributor cam. This gives me around 29 deg of mechanical advance. I
can thus set total advance (which is the sum of initial and mechanical)
to 39-40 deg, and still have an initial of 10, which allows for easy
starting. However, I don't care what the initial timing is, and I never
check it (because it doesn't matter) other than when I've had the
distributor out of the engine.
______
\___ o|
* | |
__/ /
/ 53/
\__/
|
| Stock advance weights can be ground to allow for a greater amount of advance
travel. I've found that if the area above the asterisk is ground down such that
the ramp angle is changed on the left half of the 'active'
area, the total range can be increased. The amount of clearance
between the outer side of the weight and the inner walls of
the rotor may be a limiting factor in extreme cases.
BTW, what does the number on the weights refer to? Which
weights are the heaviest? If I remember correctly, aren't
#139 weights the ones with a thicker mid-section and narrow
tip, versus the style I've depicted in ASCII, where the weight section is
widest towards the tip? BTW, the lightest factory springs I've come
across are from 1977 and 1978 425 Cadillacs.
|
[ Thanks to ,others below
for this information. ]
Vacuum Advance:
Most of the adjustable advance canisters I've used do not
advance at all when turned fully
COUNTER clockwise. Keep making runs after two clockwise turns until
you get pinging, then back off. As you have already found out, it is
important to get the car up to operating temperature before you go
through all of this or your perfect settings soon go bye-bye.
To check the vacuum advance, use a vacuum pump attached to the can and the
same timing light. Adjust the vacuum max setting accordingly.
Remember this about vacuum advance. Under light loads/throttle,
the intake charge velocity is lower and has
less mass, therefore, it burns more slowly in the combustion chamber. For
peak efficiency under these conditions, it is necessary to ignite the
mixture earlier, so that peak cylinder pressures coincide with TDC. At
heavier throttle, when the intake charge is greater and cylinder pressures
are higher, less advance can be tolerated. In other words, vacuum advance
units are used only for improved fuel economy, making better use of the
air/fuel mixture under light load conditions.
Cars have over 60° advance with the vacuum included. Under
part-throttle, low-load situations, the A/F mixture is spread all over the
cylinders, so you have to start that stuff burning well in advance if you're
to have it all burnt up by the time the piston reaches the top of the
stroke, so you crank in lots of advance. Usually you run as much vacuum as
you can before you start pinging; the exact number is irrelevant, since the
pinging will depend upon the state of your engine, quality of fuel, driving
habits and conditions, etc. Two identical engines in two different people's
cars will require different amounts of vacuum advance, though the ideal
distributor curve might be the same.
The idea behind vacuum advance is to add advance under low load, part throttle
condtions (which 3000 RPM and 18 inHg would imply) where the engine can
tolerate it. The additional advance tends to help fuel economy and
(debatably) engine cooling. Really depends on how much vacuum your cam produces.
When your foot is to the floor (high load), vacuum approaches 0 inHg and
the advance is out of the picture. My cam (JM 20/22) idles at about 15-16
inHg and I only see greater than 18 inHg at part throttle cruise so that would be
about right. If your cam idles at 20 inHg, then that vacuum advance might
result in detonation when you ease into the throttle if manifold vacuum
doesn't drop below 18. You'd have about 22 (@ 1600, say) + 18 = 40 deg.
Most folks who drag race their cars disable the vacuum advance to allow
more initial and centrifugal without having to worry about detonation when
the vacuum starts to come up at the top of the last gear.
Even a minimal amount of vacuum advance seems to make a big difference on the
low end - more torque. Although there is some pinging at highway speeds.
A fix for this is to use a vacuum advance limiter plate. The Crane
adjustable vacuum advance kit includes a plate that limits the
amount of vacuum advance that the cannister can add. I found that I could
reduce the rate or point at which the vacuum advance kicked in, but I was
unable to eliminate the pinging at part throttle until I reduced the
amount of vacuum advance, probably by about 10° or so from
the maximum it would add.
On all but the earliest HEI's, the advance canisters provide way too much
advance at way too little vacuum.
Go to your local GM dealer parts department and get the HEI vacuum control
P/N 1973511. This is the best available new. The so-called "adjustable" units.
tend to die quickly, and only control total vacuum advance. They still come
in too early.
If you want a limiter plate, and you don't want to spring the $22
for a whole Crane kit, you
can probably make one from a small sheet of heavy-guage steel, or even a
washer. Basically, it mounts under one of the screws holding down the vacuum
advance unit, and forms a kind of "stop" to limit the travel of the rod that
extends from the vacuum advance cannister. If you reduce the amount this rod
can travel, you reduce the amount of vacuum advance that can be added; this
limiter plate actually moves the starting point of the rod closer to the
canniser itself (hence you have to adjust the initial timing with each
adjustment), thereby reducing the rod's travel. The plate in the Crane kit
has a kind of serrated edge, and you adjust the amount by loosening the
screw, and turning the plate until the end of the rod rests on one of the
serrations.
[ Thanks to others below
for this information. ]
Vacuum Sources for Vacuum Advance:
Define a couple of needed terms:
Ported means that the vacuum signal varies with throttle position as
follows:
| Engine Speed | Ported | Manifold (full) |
| Idle | None | Maximum- about 17-20" Hg normally. |
| Part throttle | Some - varies w/load, speed | Some, varies w/ load, speed. Not
necessarily same # as "ported" |
| Full throttle | Very little | Very little |
Manifold
vacuum is the vacuum created by all pistons attempting to suck air thru a more or
less closed off intake. Whereas... "ported" vacuum is created by a tiny port in
the edge of the Venturi, just above the throttle plate when it is [nearly]
closed for idle. Thus ported vacuum may be a different value than manifold vacuum.
BTW, that's why at idle there is virtually -no- ported vacuum-
because the port is situated just above the throttle plate, where there is at
that time approximately atmospheric pressure which is approximately 0 vacuum.
"Ports" or nipples on carb can provide either full manifold vacuum or
"ported" depending on where they lead to/ come from. easy to check. Just apply
the finger test or the gage test at idle, then at part throttle.
Check your source by disconnecting the
hose from your canister and check for vacuum at idle (hold
your thumb over the end or use a gauge). If there is vacuum
at idle it's a full time source. A manifold vacuum source doesn't
necessarily have to be on the manifold itself; it could be a
full time port on your carb. However, a ported vacuum source will
either be on the carb or originate from the carb.
As for ported vs manifold vacuum, definately go with ported for vacuum
advance. Ported will give you no advance at idle but will increase the
advance as the throttle is opened. Sometimes with manifold you will get a
slight sputter or bog when the vacuum advance drops out as the throttle is
suuddenly opened. Experiment to find what works best for driving under
normal driving conditions (spark plug color, fuel mileage, and response).
Spark plugs can be tuned by setting the gap at .040 then opening the gap
.005 at a time until the car slows down, engine starts missing, or gas
mileage suffers. Then close up the gap to the last setting.
The whole thing about vacuum advance is drivability and fuel economy and it
doesn't hurt performance so let it be. Where you will gain more
performance is by recurving your distributor.
It dials in greater ignition advance, which is necessary when you've got a
thin or lean air-fuel mixture such as at part-throttle; you have to start that
mixture burning quite early in order to get all that fuel combusted by the
time the piston is passing TDC.
It greatly improves part-throttle fuel-economy. You can disable it
temporarily with a golf-tee plugging the line to the canister.
It also bumps your idle speed up. That's it. Makes little to no difference for
actual driving, only for idle emissions quality.
If you didn't disconnect the vacuum advance when setting the timing, it
is probably bumping up your advance as you hit third gear, since
your vacuum starts to come up as you approach top speed.
On any Oldsmobile V-8 engine, the distributer gets ported vacuum. You don't
want advance at an idle, you want it when crusing. Why do you think they call
it "vacuum advance"? Because when the engine is above idle, vacuum pulls the
points or magneto around in the distributer, advancing the timing.
No matter what brand carb you have, the distributer never gets manifold
vacuum. Even though a very, very few olds' came from the factory with
manifold vacuum. The only reason they did this is because when they put in
the distributers, if the timing would not advance enough, they used manifold
vacuum. This was easier than pulling the distributer and realigning it.
DO NOT USE FULL MANIFOLD VACUUM to the dist'r unless your shop manual calls for
that setup- I understand some later [late 70's?] Oldses did that. Not in '68
for sure.
Here's an example (hypothetical): say the spark plug fires at an idle with the
piston 7/8 the way to the top. As engine speed increases, the spark needs to
leave the distributer cap sooner because the fuel will take the same amount
of time to burn as at idle, but that will put the maximum force of the burning
fuel acting on the piston too late during the power cycle. If the spark timing
is advanced, the maximum power acting against the piston is advanced as well.
Now relate this to an Olds engine. Take off the distributer cap and look at
the internals. Make a rough sketch of how they function, especially the
vacuum advance. Think of how much advance there should be at different rpm's.
At 1000, rpm the amount of vacuum should/will be minimal, hence the timing
advance is minimal. Now at 5000 rpm, the amount of vacuum should/will be full,
hence the timing advance is full. As a final note "the distributer gets
ported of timed vacuum, not manifold vacuum".
With manifold vacuum, the timing will be advanced at an idle, and when
accelerating the timing will retard. Then when at a cruising speed the timing
advances. this final advance will not exceed the initial timing at idle.
Giving you about 8° final timing compared to 28° with ported vacuum.
If you have a long duration camshaft, you might have to run full manifold
vacuum according to the Edelbrock manual for their RPM carbs.
The url for their online manual is:
http://www.edelbrock.com/automotive/eps_sect2.html#ref
They don't tell you what is considered "long duration" though.
The installation instructions that came with my carb, very specifically
stated to use the full manifold vacuum port on the carb if the vehicle did
not have EGR. For EGR equipped cars, they specified the ported vacuum port
on the carb.
I followed the instructions and used the manifold vacuum port and the car
runs fine. I'm running about 36° of total vacuum (set with the
advance disconnected) and I did recurve the distributor using an adjustable
timing light. I also didn't worry too much about inital advance and
calibrated for total advance.
[ Thanks to Mick Gillespie, Chris Witt, Dave Dillon, Bob Barry
for this information. ]
Vacuum Control Switches:
A good explanation can be found at
http://www.crosswinds.net/~smithtp/olds/LaunchPad.htm.
[ Thanks to Thomas Smith
for this information. ]
Recurving Results:
I recurved my HEI this weekend and wanted to let everyone know what a
mileage increase I got out of it. My original '70 350 is running 10.25:1
compression, so I have never been able to run to the proper initial
timing (It pings in this hot Texas sun) At 90MPH with the A/C on, my car
averaged about 12.3 MPG (I have 2.56 rearend) I always thought that was
a bit low and seemed that it took more pedal than should be necessary to
keep it going. After the advance kit, I jumped to 19.53 MPG at the same
speed with the A/C, and it cut my pedal usage in half. The advance kit
is something that most of us have heard about at one time or another,
but often dismiss it as a gimmick. An $8 part is saving me $$$$. Note:
This result is by and far the largest gain I've heard. Typical is around
nothing to 1 MPG. Conversion from a badly tuned and maintained points
ignition to a tuned HEI system could get you this much increase.
I run an HEI w/MSD box and vac advance hooked up to ported vacuum, and
run 22° initial w/o vacuum advance with 35° total advance. Mechanical
advance is 13°. With the vacuum advance hooked up, timing jumps to over
40°. I've never had a
problem with detination or spark knock. Engine is .030" over 455 at
9.89:1 compression. Big cam and 3000 RPM stall converter.
[ Thanks to Rob Thomas for this information. ]
Advance Troubleshooting:
The distributor's curve and the vacuum advance doesn't match up since
you say that during light acceleration on the highway you get pinging, but
not at WOT.
To verify that the vacuum advance is causing the ping disconnect it and
plug the vacuum line then try to get it to ping on the highway. If it
doesn't do it fine, but if it still does it I would gravitate towards thinking that
it is pinging some at WOT but you may not be able to hear it due to other
noises (like a loud exhaust).
A high compression engine is very sensitive to initial timing settings.
Too much initial and they
tend to be hard to crank when hot. An old trick is to set the
mechanical advance springs in the distributor very weak so that
at idle the advance is partially open. That way when cranking
your timing is closer to 0 than when at idle. Another possibility
is that the starter could be getting too hot. An easy way to tell
if the timing is the problem is to pull the coil wire. If it's still hard
to crank then it's either a starter/cable problem or simply a
tight motor as Paul said.
First, what type of fuel are you using? If your using Premium unleaded
your curve seems to be a bit steep. Back off to 15° initial,
32° total, and see what happens. Keep in mind that the hotter the engine
gets the more prone it will be to detonate. The only thing to do is to
play with your curve to see where the problem is. It seems to me, on
the info given, that you have too much timing coming in too quick. You're
right that part throttle detonation can be caused by amount of vacuum
advance (not always though), but you have a lot of advance coming in
at relatively low rpm's. I would try to stretch the curve out over a few
more RPMs, and also note what RPM's you're getting the detonation at.
Try using your "slope" adjustment to make the curve angle somewhat
more "shallow". Distributor curves are a bit of a black art and the timing
computer is a nice piece, but it does nothing more than make the
black art of curve a bit easier to work with.
[ Thanks to Mike Bloomer, others below
for this information. ]
[ Thanks to Chris Witt, Fernando Proietto, Pat Clark, Andrew Green,
Bob Handren, Tom Lentz, Greg Pruett, Bob Barry, Joe Padavano, Graham Stewart,
Scott Kozhill, Scott Mullen, Kevin Wong, Chris Fair, Erik Nowacki,
Chris Ruper, Mark Prince, Rich Inacker, Todd Morris, Kurt Heinrich,
Jeff Easton, Mike Frederick, Ron Forsee, Mike Bloomer
for this information ]
Cap and Rotor Indexing
Indexing involves relocating the tab that keeps the
distributor cap in one place. What I think it takes to accomplish it is
cutting a hole in the side of a distributor cap, under the #1 terminal. The
cap is marked with the location of the inside terminal (on the outside) and
the rotor is marked with the location of the rotor tip below it's location on
the rotor's side, so you can see it inside the hole of the cap.
You start the engine and connect a timing light on #1 plug and shine it on the
distributor. This will tell you exactly where the plug is fired in relation
to the cap. From there, you can fill and relocate the cut in the side of the
distributor's base if it's really off. I remember hearing of this in a stock
car racing magazine and they said it also pays to be careful where you buy
your distributor caps, since they also can be mis-indexed.
Is it worth it? I don't know, but if you always buy your caps from the same
make and place, they should be accurate to each other. If you did this and
did find that the cap wasn't indexed properly, you could either fix the
distributor or replace it. We here at the race team are going to be real
careful about who and where we buy our caps and make a fixture to check them
this winter, and index our distributors exactly alike so there won't be any
variance in timing.
What's being done is making sure that the rotor references the proper place in
the cap. In some applications, the locating notch on the distributor's not
exactly where it should be.
The number of degrees that the cap terminals and rotor are off can't be changed
by rotating the distributor a few degrees. That would also change the overall
timing, advancing or retarding. Since the
point plate (or reluctor [HEI]) also moves when you move the distributor, the
timing would change as you move the distributor. What you are trying to do by
indexing is make sure when the points or reluctor tell the coil (to fire) the
rotor is positioned at the optimum position in relation to the terminal inside
the cap. There is an entire science in racing that looks into things like
where the best relation between the rotor and cap is for transmitting the
energy that eventually sparks at the plug. It has to do with those ten-
thousandths of a second differences in lap times or 1/4-mile ET's.
I must repeat, I'm no expert at this, I'm only relating what I remember
reading in a racing publication some time ago.
[ Thanks to Ken Snyder
for this information. ]
Table of Contents •
Index •
Acknowledgements
History •
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260 •
303 •
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324 •
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394 •
400 •
403 •
425 •
455 •
Diesel
Rebuilding •
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Option Codes •
Wheels •
Ignition •
Comp Ratio
The W's •
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Basic Tech •
How To •
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