[randy1966GTO]

Hi All,

I have a 79 T/A 403 auto car I bought 1-1/2 years ago and finally getting some time to work on it. It showed 15k miles and could be 115k or 215k, been sitting for at least 5 years. Stock looking with iron intake, original Q-Jet and stock exhaust manifolds, had spark plug extenders on 5 of the cylinders. It ran and drove (poorly) when I got it and I have pulled the engine for teardown this week and found the following:

1. Numbers matching block has cast stock-type .030" over dished pistons, no ridge and cylinders look great
2. 4A heads had these stampings on the valve cover rails: MCHS 1-5-94 (I bought the car out of Columbus, MS and this is likely Mississippi Cylinder Head Shop)
3. I assume valve job and guides only at that time, no evidence of shaving to increase compression or porting, it would show some oil smoke when running prior to teardown
4. Timing chain had a ton of slop
5. Rod and main bearings look excellent and both are .010" under (it had good oil pressure prior to teardown)

My plan for the car is to freshen the engine and tranny while I put floor pans in it and paint it, it will be a street car only with A/C and I will keep the 2.41 rear so 300-350HP is fine, it will never see more than 5,500 RPM. I need to know if the following plan is reasonable for this car:

1. Bore to .039" over and use the Keith Black hypereutectic pistons with floating wrist pins
2. Freshen the 4A cylinder heads, new valve guides and springs with new rockers and pushrods and grind down the bumps in the exhaust ports. Assuming the chambers are still around 83cc this should end up around 9.0 to 9.5 compression ratio with these KB pistons
3. Rod bolts are nice 12pt aftermarket and the rods look good, I would like to reuse them
4. Obviously new timing chain and oil pump
5. Thornton exhaust manifolds, trying to stay away from headers and this is not a max-effort build
6. I'm on the fence with the crank, turn rods and mains to .020" under or light polish and leave it at .010"?
7. Edelbrock Performer or plug the exhaust crossover and keep the iron manifold?
8. Rebuild the Q-Jet
9. Tranny shifted great but needs new seals, will I need a stall converter as well?
10 And finally, cam and lifter choice?

Thanks for any suggestions you can offer other than "put a Pontiac in it", I do have an extra Poncho engine but saving it for my GTO for now.

[455Grandville]

Unless originality is everything I’d go with a traditional Pontiac or a 455 Olds, they’re still plentiful, it’s a much stronger block as the 403 has windowed mains and Siamesed cylinders.
Back in 89-90 my buddy and I (we were just high schoolers) replaced his 403 Olds in his 79 T/A with a low mileage 1971 455 Pontiac and difference was night & day.

[steve25]

Those 403 motors / blocks have great parameters which makes me which that Pontiac would have had such a big Bore to stroke ratio motor, but the heads completely suck in regards to the size and flow provided by those heads and what tthat nice big Bore could fit valve wise!

They need in the least to have bigger valves installed and to be bowl ported!

If your keeping those stock 2.41 rear gears then the bowl porting work needs to be done by someone with knowledge of how to maintain, or better yet increase the stock level of average port velocity at street use rpm's while picking up added Torque and HP in a tad higher rpm range.

I would also consider doing a partial fill on the block.

[randy1966GTO]

Thanks for the replies guys.

I am not throwing the 403 away and won't be fully porting heads and filling the block, I don't need this engine to go over 5k RPM and the car will be a cruiser. I have the GTO when I want to go fast.

My goals here are to increase compression using the KB pistons and stock heads with stock size valves, slightly hotter cam and improve the exhaust flow a little.

My 2 main questions are cam options and can the cylinder bores be taken from +.030" to .039 over for the KB pistons?

Thanks

[1968GTO421]

After looking at Summit cams, Crane cams, Howards, Lunati cams; I think your best bet for a camshaft is Comp or Crane as they have the most choices in cams for your engine.

Here's link to Crane's catalog, Olds begins on page 152:
file:///C:/Users/User/Downloads/Crane_Master%20Catalog_2019_Low%20(2).pdf

Here's Comp's web pages for Olds cams:
https://www.compcams.com/products/co...at-tappet.html

Something with 1000-5000 rpm range should do you well.
Best of luck.

[77 TRASHCAN]

Myself and many here are against ANY hypereutectic pistons. Too many folks wasted money on them, to have a build crap out, not long after initial start up...

THe port work Steve is talking about can likely be a DYI deal. Cartridge rolls, remove any casting dingleberrys, knock down sharp edges, don't remove any surface area, to speak of, just clean things up.

Leave the things alone, that you listed as, looking good!

I'd possible look for some .030 forged pistons. It would save $$ on machine work, forged pistons are the only choice, for me. I have a 283 with forged pistons in it...

Hopefully Cliff will respond here, he has experience with all kinds of builds, and is the Q-Jet answer man.

A former co-worker of mine bought such a car as yours (a 403 79 TA), as a first car for his son. It was not in very good condition. It sounded like the cam had been changed, Had an Edelbrock Performer with the Edelbrock AFB clone carb, headers, and had a pretty high gear in it. It was black and it resembled my user name, exactly.
Dad and JR. took it the only 1/4 mile track in central Oklahoma, and that bucket of bolts ran like 12.70's, unbelieveable. Dad was riding with him, making him shift at around 5500. I drove it, just for comparison to my car, the pile of bolts really ran nice!!! A definite freak of nature...

[Schurkey]

Originally Posted by randy1966GTO

1. Bore to .039" over and use the Keith Black hypereutectic pistons with floating wrist pins

Verify compression height, zero-deck as needed.

Originally Posted by randy1966GTO

3. Rod bolts are nice 12pt aftermarket and the rods look good, I would like to reuse them

OEM Olds rod nuts are 12-point. Are you sure they're aftermarket? Stamped with a manufacturer name/logo?

Originally Posted by randy1966GTO

6. I'm on the fence with the crank, turn rods and mains to .020" under or light polish and leave it at .010"?

Does it need to be re-machined? If not...don't.

Originally Posted by randy1966GTO

9. will I need a stall converter as well?

ALL torque converters have a stall speed. The rpm depends on torque converter design/assembly, and engine power.




GM is guaranteeing millions of engines with Hyper pistons, including many of the performance crate engines--400+ hp out of a 350 small block. There's nothing wrong with Hyper pistons if you don't detonate, and if you follow KB's instructions for ring end-gap.

[steve25]

X2 on going with the slightly extra cost for forged pistons because those KB Pistons will only tolerate a little more mis tuning / Ping and knock then the factory cast Pistons, and they do not come close to what a forged piston will take of course , nor run as cool as a forged piston which could allow you to run 1/4 point more compression then the factory cast Pistons.

[Mr Anonymous]

403 at .040 over is borderline sketchy in wall thickness. Sonic test it before you do anything. Some are very thin at 0.030.

[Lee]

I've ran the KB hypers since they came out, in both Olds and Pontiacs motors. Gapped the rings per the instructions and never had an issue.

If you don't know what the rod bolts are, then how are you going to know how to tighten them? Not enough stretch and you'll be spinning rod bearings quickly, Too much and you'll break a bolt. I'd just get new rods to begin with, especially if you want to float the pins.

I also always welded up the divider on the center exhaust ports, filed the sealing face flush, then used a die-grinder to shape the port exit.

[455Grandville]

Originally Posted by randy1966GTO

Thanks for the replies guys.

I am not throwing the 403 away and won't be fully porting heads and filling the block, I don't need this engine to go over 5k RPM and the car will be a cruiser. I have the GTO when I want to go fast.

My goals here are to increase compression using the KB pistons and stock heads with stock size valves, slightly hotter cam and improve the exhaust flow a little.

My 2 main questions are cam options and can the cylinder bores be taken from +.030" to .039 over for the KB pistons?

Thanks

Not saying toss the block, just set it aside.
A long stroke Pontiac or Olds 455 is much better suited for 2.41 gears and Olds 455s have fairly thick walls.

[PunchT37]

Originally Posted by Mr Anonymous

403 at .040 over is borderline sketchy in wall thickness. Sonic test it before you do anything. Some are very thin at 0.030.

Yep. Heard that too. 040 usually max over bore. Huge bore on small block = thin walls.

[randy1966GTO]

Thanks for the many great points, I'll address them in no particular order:

Block: Zero deck, proper quench and sonic check are always in my build plans.

Rods: Schurkey is correct, I thought the 12pt nuts implied aftermarket and thanks to he and Lee for pointing me to the need for more attention to the rods.

Pistons: Agree with Lee and Schurkey that the hypereutectics will be fine if I gap rings and tune correctly and will not spend the money on .030" custom forged pistons.

Cam choice: Thanks for the links 1968GTO421 and I'll continue my research on that.

Heads: I was planning to weld up the center exhaust dividers and forgot to mention that, thanks Lee. I'll remove the bumps in the exhaust ports and do a light cleanup/gasket match to the intake but don't feel the need to do any real porting of the chambers or runners for this application.

Torque converter: I meant to ask if there is any need to go above the stock stall rating for a mild build like this, thanks for clarifying.

Randy

[455Grandville]

If you stick with the 403 and you’re pushing more power I’ve heard of girdles being put on Olds 403s as their mains are not known for strength.
Probably a good investment and I’d look into sonic testing the block.

[steve25]

I have never ever heard of a cylinder wall failing in one of these motors taken to .030" over unless it was very badly over heated which by the way cracked both heads before the block gave out!!
Geez, I mean it's only .015" off the Bore walls!

I would dispense with doing the sonic check

[randy1966GTO]

Originally Posted by steve25

I have never ever heard of a cylinder wall failing in one of these motors taken to .030" over unless it was very badly over heated which by the way cracked both heads before the block gave out!!
Geez, I mean it's only .015" off the Bore walls!

I would dispense with doing the sonic check

The bores are already AT .030" over, I wanted to use the KB pistons at .039" over and will sonic check. Girdle would be a waste of time and $$$, this car will be a mild performance highway cruiser on a budget and will not be driven anywhere near hard enough to hurt it.

Thanks everyone for your inputs!

Randy

[takid455]

Randy
Set you a PM on a rotating assembly I have.

Sent from my LG-G710 using Tapatalk

[455Grandville]

Originally Posted by randy1966GTO

The bores are already AT .030" over, I wanted to use the KB pistons at .039" over and will sonic check. Girdle would be a waste of time and $$$, this car will be a mild performance highway cruiser on a budget and will not be driven anywhere near hard enough to hurt it.

Thanks everyone for your inputs!

Randy

Then you should be fine.