502 Chevy - compression ratio?? - Lateral-g Forums

h0tr0dder_uk · #1 02-15-2008, 05:37 PM

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

Vegas69 · #2 02-15-2008, 05:42 PM

Quote:

Originally Posted by h0tr0dder_uk

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

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.

Hotrodrobert · #3 02-19-2008, 12:01 PM

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??

h0tr0dder_uk · #4 02-19-2008, 12:58 PM

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.