Spinmonster

needed to know how much of a drop in CR I will have from 2cc diamond pistons and how much do you shave the heads to make up for it.

Thanks for your best educated guess

71CamaroLS1

Assuming you're starting at 11:1, you have a combustion volume of 70.9cc right now. Add 2cc, you have a combustion volume of 72.9cc, which yields:

(709cc + 72.9cc) / 72.9cc = 10.73 CR

If your starting CR is different, the calculation will change very slightly, but an assumption of .25 CR loss will still be close enough.

Combustion chambers lose about 1.5CC for every .010 milled off, which means that milling about .013 will recover your 2CC loss.