502 Chevy - compression ratio??
 

I seem to be having some trouble working out compression ratios for my ZZ502 Chevy engine. I know that its 9.6:1 with 110cc heads (4.470 bore, 4.000 stroke). The HO502 uses the same psitons but a 118 cc head and has 8.75:1.

When I enter all these details into some of the online compression ratio calculators I can't get them to add up ?!?!?

The reason I am doing this is that I want to lower my compression ratio as I'm running a blower. I intend to fit a pair of 121cc cnc ported heads and want to know what CR that would give me.

Any ideas:question: :question:

As long as you run the same head gaskets as the HO502 and the pistons are in fact the same then it would be slighly less than 8.75:1. I am sure an expert will chime in.

Adding 3cc to chamber volume, no other changes, it will be about 8.5:1.
The difference in the cr is not enough to make much difference so unless you are after more air flow(more HORSEPOWER) you don't need to change heads.
I have done a bunch of blower boats and a few cars and the AFR's outrun everybody out of the box. Yes, I have done a few back to back on the dyno to be sure.
How many are you trying to make??

The engine is putting out about 700-750bhp at the moment (with 9.6:1 CR and the blower underdriven). I was hoping to drop the CR by changing the heads and be able to overdrive the blower and make more BHP. I don't think theres a manufacturer that makes a direct replacement low compression piston for the ZZ502.