2020-B4-3

Author Topic: 79 T/A 403 rebuild plan  (Read 194 times)

GT/AO

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79 T/A 403 rebuild plan
« on: December 28, 2020, 08:40:57 AM »
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 300-325HP is fine, it will never see more than 5,000 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,

Randy
1966 GTO and 1979 Trans Am on the way

olds403

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Re: 79 T/A 403 rebuild plan
« Reply #1 on: December 28, 2020, 09:51:04 PM »
My advice is the following.
Early 330/350 heads or big block heads*. Would not use 4A heads or the KB’s. 
Race tec pistons.  Much nicer.  I suppose you will go .039 overbore
Custom cam - use Mark Remmel.  He has done several Erson/lunati for me.  He goes by cutlassefi on classicoldsmobile.com.  He knows me well. He can get the pistons, cam, and get any heads done.
He will do complete motors, but very backed up. 
Tell him Mike sent you. 

*Big block heads will need RPM intake and custom air cleaner base for the shaker. 
I did a early 350 head motor last year 2019.  I do have two sets of #4 1967 330 heads for sale. 

Who is going to do all your machine work and build the motor ?  Budget ?
Final thoughts are that rear end gear really limits you.  Consider 3:23 and 3 series carrier.  Will be a whole new car wiith a nice motor and gear swap.

GT/AO

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Re: 79 T/A 403 rebuild plan
« Reply #2 on: December 29, 2020, 10:05:30 AM »
Thanks for your inputs.

My low budget doesn't include different heads or changing the rear end and the car will be a mild performance highway cruiser. No need for the Performer RPM, it won't be revved that high.

I'll have someone in the DFW area do the machine work on the block and freshen the heads and I will assemble the engine.

Regards,

Randy
1966 GTO and 1979 Trans Am on the way

olds403

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Re: 79 T/A 403 rebuild plantroke5
« Reply #3 on: December 31, 2020, 12:06:22 AM »
Those 403 KB pistons were designed by Terry Fritsch in the early 2000’s. 
Not a good piston. Heavy and not forged.  You can get custom Racetecs for nearly the same money and a better piston.  Many other options now with modern rings low friction.  Not a fan of those KB’s.  Dont just take my word for it as used them  - see reviews on summit racing.  Hit/miss.  I practically gave our sets away. 


Save you a lot of time.. cast pistons .030 over.  Sealed power .  Zero deck block.  Early 350 heads #4, #5, #6, #7. 
Will be good mild performance buiod and will all fit up and work.  4A heads are not worth putting $700 pistons and rings,  Use that money on early 350 heads and cast pistons.  Just deck the block to zero.  That is what I’ve done and worked well. 

Might want to jump over to classicoldsmobile.com.  Not many post here anymore. 

Gold member

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Re: 79 T/A 403 rebuild plan
« Reply #4 on: December 31, 2020, 04:54:29 PM »
403 Just  got done adding the # 7 heads the sound coming out the tail pipes sounds impressive compared to the 4a heads . I wont be able to test drive till spring but i have a feeling i will be happy.
1979 Gold Bird
original paint and decals motor and trans   solid body mounts   frame connectors  full suspension overhaul  255/50/17 Nitto tires and YO snowflakes .  
Jim

olds403

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Re: 79 T/A 403 rebuild plan
« Reply #5 on: December 31, 2020, 08:21:56 PM »
Early heads best bang for buck.  Really wakes up the 403.  Cut heads to 62cc and nice cam.  Hold on.
No need for crazy mods unless you are maxing out the 403.  We did a 424 stroker 403 and was quite expensive

Re: 79 T/A 403 rebuild plan
« Reply #5 on: December 31, 2020, 08:21:56 PM »
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