# Compression ratio increase



## cfd2bc (Jun 11, 2011)

Hello all. I have a 66 Lemans and just picked up a low mileage 400. It is a 1979 though and from what I understand has only about 180 hp with 7.5:1 compression. Can anyone tell me how much I would need to mill the head to get that up to around 9.5:1? I have a 2802 summit cam I want to use but requires that compression. 
Thanks, Jeff


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## BearGFR (Aug 25, 2008)

Which heads does it have on it now?
(reference: Pontiac Power)

Depending on which heads you have, it may or may not be possible to mill them "enough".

Bear


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## cfd2bc (Jun 11, 2011)

That's a good question. I'm not sure. I will take a look this weekend and let you know. 

Jeff


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## geeteeohguy (Feb 2, 2008)

And to remove enough from a large chamber head (100-114cc) to make it 82cc would require serious surgury on the intake manifold and probably shorter pushrods. My advice would be to ID the heads and go from there. If they are super low CR, get a different set of heads.


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## pontiac (Mar 6, 2011)

can't do it sufficient on large chamber heads. Get other heads.


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## 69Goatee (Aug 14, 2009)

I had a 1976 400 for my GTO as a surrogate engine while I was rebuilding my numbers matching engine. I can't remember what heads it had on it, but they were small valve/pressed in rocker studs. And the pistons were the multi-valve relief deep dish, ultra low compression. I put a mild cam in it and my 72cc #62 large valve/screw-in heads from the #'s matching engine, and it ran good, not great. I bet you have the same pistons in your engine, best performance gain is to change pistons. You said it was a low mileage engine, you might get away with just a hone on the cylinder walls and new pistons and rings. You also might be able to use the stock heads to save some cash for other parts.....until you want more power again.


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## cfd2bc (Jun 11, 2011)

Thanks for all of the input. I decided to just put the engine in the way it is and run it stock for now. Hopfully I can build something in the near future with more HP. 

Jeff


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## danthepontiacman (Jul 5, 2008)

not sure bout how it do on a 400 but 2v 326 engines were rated 9.2 cp in 66 and 67, more inportantly there cheap on flebay ha:cool


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