General Information
Note: The information contained in all
of the "Engine Detail" sections should be read before proceeding with
modifications, etc., because some information that applies to all engines, or
all small blocks or all big blocks, might not be duplicated in every section.
The 403 was made from 1977 to 1979 and used across the Buick, Olds, Pontiac
and Cadillac vehicle lines. It was also used in other applications like
motor homes, boats and some industrial applications. It was sort of meant
to replace the previous use of big block engines in the BOP line.
Stock specs on a 1977-79 403 are: 185hp@3600 RPM, 320ft/lbs torque @2200
RPM, 4.351 x 3.385 bore/stroke, 8.0:1 compression ratio.
Big pistons and a short stroke are an excellent combination for a high-RPM
engine, but here the other inherent 403 weakness comes into play: Windowed
main webs, and to a lesser extent, siamesed cylinders. The bottom end of
this block is not suitable for extended use at
high rpm with very high cylinder pressure.
Sources For 403s
| 1977 | Cutlass, Vista Cruiser, Delta 88, Custom Cruiser, 98, Toronado, Electra 225, Bonneville |
| 1978 | Delta 88, Custom Cruiser, 98, Toronado |
| 1979 | Custom Cruiser, 98 |
[ Thanks to Fred Nissen, Jason Adcock, Bob Barry for this information. ]
Streen Machine
If you are looking for a super reliable street engine
that will squeeze the absolute maximum torque into
an 87 octane, cheap to buy, pollution legal till 1979, minimum
weight package that is a direct bolt in (including
weight) for any Olds small block, try a 403.
Here are my results:
Stock 403 from 1978 Toro, new timing chain, Jacobs
ignition, diesel sized 4" tall K & N air filter (extra low
Toro bottom half, tall diesel top half), dual 2 1/2" pipes
with crossover and no cats, switch pitch transmission
with electronic controller, 2.41:1 axle and a 4100 lb
RWD car. Measured many times with my stopwatch
and also with VC2000 computer: 0-60 7.49sec; 1/4 mi
at 91.2 mph in 15.86 sec. The slow time reflects the axle
ratio; the car has gobs of power between 70 and 100
mph, as I have enjoyed demonstrating to many cars that
were more nearly matched with their 4 speeds at 0-60
including a certain Mercedes sports car who thought
he could top end me after I blew him away at the line. I
estimate 270 horsepower by modern measurements by
comparing it to the published times and weight of many
modern cars. Is this a race car; NO. It is a very practical
street car which has seen 20mpg (NOT with me driving) and
the only car I have ever owned to get to 300,000 miles
without once seeing a tow truck
It's not quite pollution legal with no cats, but it would
pass our test here that way.
[ Thanks to Bruce Roe for this information. ]
Main Bearing Webs
The main bearings are supported in/ connected to the block with webs of cast
iron. Later motors, after 1976, including the 403's [most, anyhow] had not
solid webs but webs with holes. Thus, there were essentially 3 fingers of cast
iron holding each main bearing.
Good luck finding a Solid Main Web 403 motor. Rumor has it that some 403
blocks were made w/o holes in the webs- Solid Main Web 403's.
Supposedly 403 solid main web blocks are found in the Pontiac Bonneville with
the towing package, and in some 1979 Pontiac Trans Ams with
a towing package.
Then again, for all but 600HP race motors,
it's not necessary; the metallurgy of the 403's is quite well done.
[ Thanks to Chris Witt for this information. ]
Siamesed Cylinders
The design does have some limitations due to the siamesed cylinders and
windowed webs. You must insure the cooling system is large enough and in
good order. I would not recommend one for an ultimate dragstrip build up,
and I would avoid doing anything that greatly raised the compression
especially if the block was overbored. Head gaskets blowing would be the
concern here.
[ Thanks to Fred Nissen for this information. ]
RPM Maximum
The 403 is a mediocre all out performance engine. The main bearing webs are
the weak link and the engines can usually accept only a .040 overbore. They
are thin. Yes you can bolt the mounts off the 350 right to the 403 and drop
it in. As for supercharging you need to look to a different engine assembly. A
350 or 455 is a much better choice. Danny Lattimore has a stock class 403 in
a Trans Am that turns 7500 RPM. So things can be done but at a major cost.
Sure, you could build a 7,500 RPM motor, but it'll cost you a good chunk
of change. In the U.S., you'd have to dip to the hip for likely two or
three thousand dollars (and that's at the *cheap* end of the spectrum).
Seven, maybe seventy-five hundred is possible with a windowed
main web engine, and even then it's under serious stress.
Once again, why do you want an engine that can rev this high? Yes,
NASCAR mechanics can build a 9,000 rpm motor, but they have to be
rebuilt every 500 miles.
First of all, you'd need a forged crank, which should be good up to
seven or seventy-two hundred. After that, you'd need forged pistons,
and they're pretty costly here in North America as it is. What are
prices like in the Netherlands, anyway?
Add in a wicked cam, large valves, strengthened valve-train and
pushrods, and a set of *really* stiff valve springs, otherwise they'll
float off of the pushrod, and your power will be flowing out your
exhaust pipe. (not to mention that the valvetrain would fly apart after
a 1/4 mile at 8,000!)
There are a few different ways you can boost up the compression, which
would help with a wild cam: you can shave the heads, which makes the
combustion chamber closer to the piston head. Or, you can buy pistons
that can kick up the compression. Most pistons have two reliefs cut
into them, which eliminates the possibility of having a piston slamming
into a valve. You can buy pistons with smaller cuts in them, which
raises the compression. Just make sure your cam timing is perfect, and
be sure that a valve won't stick open. Otherwise your piston and your
exhaust valve will get married, and you'll be buying them one expensive
present!
OK, ok, theoretically speaking I suppose it could be done, since the basic
geometry of the 403 is pretty decent. You could probably get 8000rpm out of
a 403 if you:
-
Start with a solid-main web block (if they in fact exist), completely
blueprinted, and filled the lower water passages with block hardener and use
a full block girdle. O-rings would be a definite *must*
-
Used *Ultra* lightweight forged pistons, and absolutely used aluminum rods
-
A billet crankshaft would be called for, though if you like living on the
edge, a factory 330 crank could be used, though I'd want to magnaflux it
about every 10-15 passes.
-
Batten heads, *heavily* ported, with the biggest possible valves, might
just get you to 8000rpm.
-
Fabricated sheetmetal intake, with at least 1400 cfm sitting up there.
-
Huge tube headers
-
Crank-triggered ignition
-
.700"+ lift solid cam, aluminum rockers, titanium valves
-
External oil pump, perhaps dry sump, or at least a stock system with the
standard mods and external drain-back lines. It would be good to have more
than 8 quarts of oil circulating in there.
The basic geometry of the 403 is very similar to the Ford or Chevy 302's,
which are capable of being high-winding motors, so whatever you do to them
should work on the 403. The big problem would be finding a solid-main block,
without which this buildup would simply be a kamikazee run (i.e. you'd see
8000rpm with this motor... once).
If you could find a suitable block, though, you could probably put together
the above motor for $20,000. It might produce 800-900hp, and have an
effective power band of 5500-8500rpm (I'm just guessing here; somebody here
might want to run these numbers through one of those dragstrip Jr. type
programs to see what it really would do).
Wouldn't be that much fun to drive a car with that engine on the street, though.
Once again, the compression can be boosted a lot, by small-dish pistons
and/or smaller chamber earlier small block heads. Open up the breathing with
free flowing xst, big valves, port the heads, nice intake & carb... Rowdier
cam, much stiffer valve springs, the usual tricks. Improve the oiling system.
Match the timing curve to the new attributes of compression, cam, and fuel
used.
On a side note, I remember Dave Smith building a 403-based engine to try out a trick
main girdle to strengthen the bottom end on those lightweight blocks. It
cross-bolted the custom main caps, supplemented with studs at the original 2
bolt locations. He brought it out to Orange County on a test day and had Tom
Chelbana run it a time or two. That's all it got -- the girdle worked, but
the webs inside the block broke. I don't think Dave ever tried another 403
that way, the diesel block's just too much better and his main caps for it are
the only way to fly.
[ Thanks to S. Dave Ward, Ken Snyder, Jim Chermack, Chris Witt, Bob Barry
for this information. ]
Buildup
Actually, it seems to me that the 403 should be a kick-@$$ motor. Besides
just slipping in over the mandatory 400 cu in limit ;-), the bore/stroke
ratio of this thing is incredible. The thing has a bigger bore than a big
block Chebby. If you relocated the valve centerlines in the heads, you
could run some impressive valve diameters, with the result that you should
be able to flow an incredible amount of air. Think about it: many on this
list sing the praises of the short-stroke 400 motors - here is essentially
the same motor with a better bore/stroke and a smaller/lighter block. Why
aren't there more of these out there kicking butt? The ultimate Olds motor
might just be a 403 (yeah, good luck finding a SMW block - anybody thought
about welding up the windows and doing an align bore?) with a forged 330
crank and Edelbrock heads with relocated enormous valves. The smaller
bearing diameters would also reduce bearing speed and thus friction. I may
just have to build one of these.
The 403 responds well to a bit more camshaft and compression. I used
earlier 350 heads ('68-'72 will do it, but the '72's are the best) to raise
the compression, and an Edelbrock Performer-grind cam (these cams are
available from other sources than Edelbrock, who I suspect purchases them
from another supplier).
A true-dual exhaust really livens up the motor; the factory crossmember
from a pre-'75 (year of mandatory catalytic converters) allows true duals
without excessive bending, though you'll have to check with emissions laws
regarding keeping or discarding your catalytic converter.
The next upgrade on my list is a change from that 2.41 rear axle ratio;
while my engine improvements improved bottom-end power (it can roast the
tires at will off the line), the real improvements come into play above
3500 rpm, which means my car really starts to take off at about 70mph in
second gear. I plan on moving to a 3.23 rear gear, though moving to a
beefed 4-spd automatic with Overdrive would allow me to move to a 3.73 rear
gear. I don't make enough hp to justify a Gear Vendors overdrive ($2800!).
The 2400rpm stall converter in front of a TH-400 improves the launches of
my car.
[ Thanks to Joe Padavano, Bob Barry for this information. ]
Block Boring:
An Olds 403 can only be bored out 0.040" before problems with cooling can
occur. The siamesed cylinder layout (no cooling jacket between cylinders),
and the minimal iron between cylinders is the cause of this limitation.
Well, after a 300+ mile journey with my often-hot running 403, a 403 should
not, at least for a car that sees any kind of traffic or distance driving, be
bored .060 over.
After watching my temp gauge hover at 250 for over 10 miles of uphill
driving at 70MPH, (and the oil pressure fall to 15PSI at that temp, from the
normal 30) I am somewhat disheartened, but not really surprised. Going up
those hills, I had plenty of opportunity to "play around" by flooring it (to
see if richening the mix helped at all..actually got no hotter or colder) and
watching the temp, but the temp was pretty constant depending on terrain. 220
on the flats after the hill climbing was about the norm. Very rarely did it
drop back down to the 195 the T-stat is rated for. Coasting at high speed
(neutral) did drop the temp very quickly, so I know the radiator is working
real good.
Another person has overheated a stock 403 (stuck thermostat) three times in two days,
shutting the engine down right after each occurrance on a 70,000 mile engine.
Now 13 years later and at over 215,000 miles, the stock 403 is still running
strong.
With a bored 403, or even stock 403, keep the cooling system in A-1 condition.
Drain cooling system (radiator, block drain plugs, etc) at least every 3-4 years.
Use a cooling system additive that promotes the thermal transfer of heat from
the engine to the coolant (Water Wetter, Sy-Cool, etc). I would avoid using any
form of stop leak! Use a 6 or 7 blade fan,
radiator shroud, 3 row or more radiator, and keep the lower air dam in place.
If you can get away with it in your climate, use a 30/70 ratio of coolant to
water to enhance the performance of the cooling system additive. A thermostat
rated at lower than the stock 195° unit might help as well. But the problem
is really with the ability and capacity to transfer heat than overall temp. The
ability and capacity to transfer heat directly affects overall temp.
[ Thanks to Dorian Yeager, David Brown for this information. ]
Short Block:
- 330 forged crank for operation over 5,000 RPM.
Heads:
A stock 403 Olds engine has tons of torque. Carbs aren't the problem.
The problem is the heads. Their combustion chambers are too large, around
83ccs. This results in a compression ratio around 8.0 to 1.
Try to find a set of 350 heads from 1973 or before. This will raise
compression enough to even think about HP. Before you think about a carb
I would think about an intake manifold, if your's is stock.
If you add 72 or earlier
350 cylinder heads, your compression will be abound 9.5:1-10:1. It will
increase your HP considerably, though you'll probably want to add a cam that
can take advantage of that high compression. If matched with an Edelbrock
intake, I'm guessing around 300 hp, though that's a really rought estimate and
depends on the parts that you use. Most 350 heads will boost compression, not
much boost from the common #8 heads.
Yeah, what he said.
My calculations say that unmachined 64 cc heads such as '68 to '72 350 heads
would boost the stock 403 to 9.50:1 compression. Mill the heads 0.030" and you
have just over 10:1 CRatio. This assumes 0.040" head gasket, and a few other
assumptions.
This is my recommendation also. Get '72 350 heads [hard xst seats], install the
403's bigger 2.000 valves or even larger W30 2.072" valves, and limit your
expenses. That motor will kick ass w/ the appropriate cam, intake, exhaust. As
for those who doubt the ability of the 403 to handle power with its open main
webs, you might call a racer who uses one, such as:
The stock 403 heads have 4 additional coolant holes drilled for additional
cooling (because of the siamesed bores), compared to 350 heads. Drill these
additional holes in any 350 heads you might use for additional cooling
potential and additional protection from blowing head gaskets. This advice
comes from a number of experienced rebuilders and Oldsmoholics.
Don Dagget 517-886-9295 (might not be correct).
Mark or Dan Van Koevering 616-453-0497 or 956-3378 [extensive experience]
Runs 403 to 7,000 rpm. No bottom end mods. Still OK. Better metallurgy.
A high compression 403 will not shatter a stock piston, unless you are
running nitrous. The
"7a" heads only give you about 9.5:1 compression, and the factory
high-compression 350's came with 10.5:1 and cast pistons, so you're pretty
safe. Just have it balanced, and keep her under 6000rpm.
- Any 350 head will raise compression a little to a lot. Depends on combustion
chamber size.
- A set of 1968 to 1972 heads will raise compression, and allow the engine to make
more power.
- Use the 2.00" intakes from the 403.
- Ream the head bolt holes for the 403's ½" head bolts.
You'll have to use premium gas, and perhaps recurve the distributor.
As far as heads are concerned, my personal choice would be a set of big block
heads with big valves. Given that the 403 small block obviously moves as much
air as the 400 big block, why strangle it with small block heads? Adapting the
big block heads to the 403 requires a couple of things:
-
You'll need to open up the 7/16" head bolt holes in the heads to fit the 1/2"
head bolts used on the 403.
-
The Performer small block intake has enough meat to allow the runners to
be ported to match the larger big block head intake ports. You'll either need to do this yourself or
pay someone to do it.
Edelbrock aluminum heads would be great, but that's an additional
$1500. Stock big block heads with 2.07/1.625 valves will be more than adequate
for this motor, especially if you can do a simple cleanup on the exhaust ports
to remove the A.I.R. bumps. Also, have the exhaust flanges milled or welded and
milled (as required) to ensure that the divider between the center two exhaust
ports goes all the way to the flange surface. You will also need to run the
numbers on true compression ratio with your pistons, head gaskets, and head
chamber volume. Most stock big block heads run about 80 cc in the combustion
chamber, which will be a little large for your 403. Of course, milling the
heads will require you to check pushrod height and possibly run a non-stock
pushrod length. If you're planning to do some work to the heads (milling and
exhaust port cleanup), the smog-motor J heads will be fine. These have hardened
valve seats and if the exhausts are ported will flow the same as the harder to
find (and priced accordingly) C heads.
When you're done, you should have a small block Olds which will run as well as
the vaunted short stroke 400 motor of 66-67.
[ Thanks to Ian M. C. Dixon, DrkSole, Chris Witt, Bob Barry. Joe Padavano
for this information. ]
Head Gaskets
I blew another head gasket in the 403 (other
side this time, so it's got all new gaskets) in the same manner as I did the
other side last year; I had driven on a hot day, parked it, and revved the
motor after it had sat for a little while.
It seems that the 403's need a constant flow of coolant to keep everything
nice and square; when you let it sit, the nice cool (relatively speaking)
radiator fluid keeps that thin bit of iron between the siamesed bores
somewhat straight, but when it's shut down, the heat from the engine evens
out, and the cylinder walls perhaps distort. Then, when you give it
full-throttle shortly after starting the engine when it's hot, the high
cylinder pressure (I've got 175psi static pressure, plus 16' initial timing)
can blow out the gasket between the cylinders.
I neglected to pay attention to a rule I made for myself, to not rev the
motor for at least five minutes driving time after starting it hot. I might
add in a recommendation to O-ring any overbored 403's with small-chambered
high-compression heads when you're doing other machine work, unless you
don't mind an annual head-gasket change.
Oh, and the fact that I've got properly-torqued ARP head bolts doesn't seem
to make any difference in this. Those big pistons are part of the 403's
weakness; the large bores leave
little room for the head gasket, which limits the amount of cylinder
pressure you can develop before blowing a head gasket.
[ Thanks to Bob Barry for this information. ]
Valvetrain:
Induction:
[ Thanks to for this information ]
403 With a 425 Crank
If I win
the lottery (which I don't play), I'd tool up for some 403 castings with a
diesel bottom-end to take the 425's crank. I'm still scheming about a 425
crank with cut-down journals being dropped into a 403 block; I _want_ a
500+ci SMALL BLOCK! Of course, I'd have to put 260 stickers on it... :)
[ Thanks to Bob Barry for this information. ]
Buildup Examples
'87 Cutlass
I have a 403 in my 87 Cutlass, and it performs very well.
The 403, stock, is only about 185 hp, but 320 ft-lbs of torque.
This is what it has in it now:
| • .030 over bore |
| • 72 350 heads |
| • Edelbrock performer RPM intake |
| • Crane cam (.480"/284 degrees (intake), .496"/292 degrees (exhaust) advertised (at 0 degrees)) |
| • Crane lifters |
| • Crane valve springs |
| • Summit True roller timing chain-cast piston 9.5:1 |
With these not-so-expensive upgrades, my car runs mid 13's.
'79 403
| • '79 403 block bored .030 over => 409 CID |
| • 403 crank ground .010 |
| • stock 403 rods |
| • Arias(?) forged aluminum pistons, 10.5:1 |
| • Crane Cam .480/.496; (280-290 adv.? cam card missing!,
maybe 292 or was it 272, dual pattern though, both with some high 200's
duration (advertised) |
| • Crane lifters, pushrods and springs |
| • '72 350 (7a) heads |
| • Edelbrock 7111 performer RPM intake |
| • Carter 750cfm AFB |
| • Mallory Unilite distibutor w/ Cccel supercoil |
| • TH-350, stock converter, shift kit |
| • 3.08 posi |
Recently smoked a 96 Vette (since we fortunately didn't reach the point
where he'd be in 6th gear!). 5.0's are effortless, generally, non-blown
ones at least.
[ Thanks to Ray Costanzo for this information. ]
1979 H/O
| 1979 Hurst/Olds
|
| Built Racing Head Service 403,
|
| Mondello JM 22-25 cam
|
| W-31 heads
|
| Edelbrock Performer intake,
|
| rebuilt Carb Shop quadrajet
|
| Holley electric fuel pump
|
| less than 100 miles on rebuilt Turbo 350 & B&M 11" converter
|
| 3.23 Auburn posi unit
|
| Hellwig swaybars
|
| new dual exhaust
|
| solid body
|
| fiberglass cowl induction hood
|
| Hurst dual gate shifter
|
| original Hurst wheels w/ good BFG tires
|
| Runs VERY strong at 13.1@ 105 mph 1/4 mile
|
[ Thanks to Todd Evans for this information. ]
'80 Cutlass
I had a 1980 Cutlass with a 403 stuffed in it. It ran 13.60s stock with street
tires, well semi stock.
| Stock rebuild |
| moly rings |
| Edlebrock intake 3711 |
| Comp Cam's cam (I believe the one with the 433 lift and 262 duration) |
| 650 dual feed double pumper Holley carb |
| dual 2.5" Flowmasters |
| TH-350 trans with shift kit and no stall (with stall I would burn up in
the gate) |
| 3.73 rear end |
With that combo I beat almost every Chevy on the
west side of Chicago and Ford Mustangs couldn't stay there either. Believe me
with a light body and the right gear, you can't lose with a 403. It came stock
with 185 horses and 320 lb. of torque. They called me the green machine from Ogden and Kosner.
[ Thanks to Samuel Johnson for this information. ]
Rebuilding
403 on $500
Well, for that price, you'll have to stick with your stock shortblock, and
the stock intake, carb and ignition will have to serve.
Under that budget, however, you might be able to address the two main
weaknesses of the 403: the cam and the compression.
A set of 7a heads from any '72 350, with your 403's stock 2.00" intake
valves, will raise the engine's compression and improve its exhaust flow.
The purchase price and machine work will cost you around $400.
A decent cam like the Mondello JM18-20, the Edelbrock Performer or even the
'68 Hurst/Olds cam with new lifters (and springs, if you can afford them)
and a new timing chain, will make a noticeable difference as well.
In all the above things, the details (such as degreeing the cam,
port-matching the heads and manifolds, etc) are the most important thing,
and will maximize the gains you realize from these modifications. Needless
to say, the above price estimates will not include labor, and neither of
these mods are "bolt-ons", but they will be the most effective.
Any other mods above and beyond the heads and cam would be geared toward
improving the durability of the engine, but wouldn't necessarily contribute
toward power output in any dramatic way. Those kinds of mods will go way
beyond $500, though (things such as forged pistons, oiling system mods, rod
and crank preparation, balancing, etc.).
[ Thanks to Bob Barry for this information. ]
Heads
Consider swapping a set of earlier 64cc heads onto the engine. See Buildup above.
Tuning / Power Boost