That formula varies from head to head. Like the small blocks are like .0067 or sumthin like that equals one cc. It's sumthin you kinda have to figure out with each head. And I don't necessarily think it's the same for every kinda the same head, either. Cause with all the variations in machine work and blah blah blah you're gonna see differences everywhere. Best thing to do is just tell the machine shop "I want the chambers to equal "X" amount of ccs when you get done."