how do you calculate compression ratio?

OrangeMustangGt

Founding Member
Mar 7, 2002
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Cape Cod, MA
I finally found my machine shop for my gt40p heads.

I was worried the reason my car was detonating was because i had them milled.

They were both milled .004......How much would this raise compression ratio?

the milled heads may not be the reason i was detonating if .004 dosent affect that too much.

How can i calculate compression ratio? I think p heads have 58cc chambers, but how do i get an actual number from that?