Andy- I can see how you would calculate clearance given those TDC numbers provided by Comp or whomever. But how do you figure it out for the rest of the duration? I'm presuming the valve could hit at other spots than TDC. I can't see how you figure out what the lift will be at the other degrees of the cam. At least with the piston, knowing that the crank swings in a circle at a certain throw, the rod length, piston height etc, I can see where you can calculate where the piston will be at every degree. I just can't figure out how I can calculate the lobe lift (or valve) across the degrees of a revolution.