Well, you can get with an on-line compression calculator. Know the specifics of the parts that have the inputs values, like a head gasket. You’ll need to know how thick it is compressed and how big the bore is on the gasket. An all the other parts. No guessing. Especially, with a piston sits in the cylinder bore relative to the deck. If the piston has 6cc’s sort of valve relief area, you can simply add that to the cylinder head cc amount.