Depends on what the configuration of the piston dome and compression height is on the piston Bob..... If you're ordering it as a stroker kit then the company selling it will have a chart saying what the CR will be with different CC heads. Or, you can run the whole formula for CR and see if yours comes out at a number commensurate to run pump gas on. My engines were either on race gas and then on E85 which allows the engine to have a whole bunch more compression!!!! Aluminum heads are generally good for 10:1 CR on pump premium, as long as you don't get too crazy on the timing!