So I purchased a partially finished 1970 400 ram air lll (block 9799914). Uncle passed away and I was able to purchase. Bottom end has been bored .040, crank shaft ground, forged TRW pistons and the original ram air cam. Unfortunately he is not here to ask what direction he was going, only able to go off receipts from the build. He also had a set of #12 heads that need to be refinished. I believe the compression ratio will be way to high for todays gas with these heads. Is it better to go with dished pistons or just a different set of heads? Would like to get back to original power or closer to 400 if possible. Any ideas or direction would be welcomed information. What would you do?

How far down in the hole are the current pistons?

Plenty of people are running engines today at high 9 low 10 compression ratios on premium gas(93 here in Texas). The recipe generally includes zero deck height between 0.035 and 0.045 quench height and an appropriate cam. Is it the 068 cam or the 744 cam that you have?

Unless it's going into a '70 model car, in which you want a correct numbers RA3 engine, I see no reason to use the #12 heads.

I personally would sell the RA3 parts to somebody who must have 'em for their RA3 resto.

But, if you wanna use the block & heads, AND get 400hp. I'd buy a dish piston stroker assembly from Butler. Easy pump gas 400hp/500 torque, with a mild cam.

If you wanna use the block, but not the heads, I'd go with a flat top stroker assembly & 6x-8 heads.

If you wanna use all the parts you have, I suppose you could have the chambers enlarged, to reduce CR. Then use a cam with lots of adv duration, like maybe a Summit 2802, or even an 041 clone, with Rhoads lifters.

Obviously, the 3.75 stroke engine will have less low end torque. So, it all depends on exactly what you want from it.


"...1970 400 ram air lll...the original ram air cam..."

The original cam would be an 068. A lowered compression 400 won't make near 400hp, with an 068, IMO.

Ill have to look to see which cam it is. Stamp is on the front under the timing chain correct?

I would sell the engine to someone who
has the matching (period correct car).
Buy a short block with the proceeds.
You will get an excellent driver engine
and for less money in the end.

First, what is your budget...?
I'd check the deck height and if you have the coin go with a set of ported aluminum heads. I've heard you can run 72cc chamber on premium gas w/o issue.

I went with flat-tops and a set of 6x-4 heads which has a 87cc[?] chamber. The 6x-8 was a 455 head which is ~100cc

"...6x-4 heads which has a 87cc[?] chamber. The 6x-8 was a 455 head which is ~100cc.."


Just to keep all the facts straight, the 6x-4 heads are said to have chambers closer to 93-94cc.

The 6x-8 heads were used only on 400 engines, NOT 455's. They're supposed to have aprox 100-101cc chambers.

http://wallaceracing.com/head1.htm

http://www.classicpontiac.org/FAQ.asp?myPage=V8HeadInfo

To know your actual chamber size FOR SURE, they MUST be measured. Size from the factory can vary, and the chamber volume could have been changed by previous head work.

9:1 compression 400 with factory heads making 400hp is no problem.
You don't need that stroker junk.

Zero deck..

Custom pistons..

Take the engine to Butler or Kauffman..tell them your intent..trans type, carburetor, rear ratio..etc and they will build you a stock looking pump gas engine with a custom grind that will make you grin.

Dont....I repeat dont...take a Pontiac engine to the corner .machine shop unless another Pontiac guy vouches for his build.