502 Chevy - compression ratio??

[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