Really? I'm not explaining it..
I will say this, If you know the cam lobe specs and it's timing relationship to where the piston is in the bore, then you can get pretty close. Once you get the cam, then you can do a final measurement .
I don’t need you to explain anything. Your answer that if you know the valve drop at TDC you know your P/V is wrong.
The valves are not at their tightest point at TDC. So there’s that. And second, when you add in valve train flex (because using checking springs won’t tell you how much P/V you have either) you still won’t know what your P/V is.
With valve drop (or more correctly VOTDC or valve opening at TDC) all you know is exactly that. How far the valve is open at TDC. It has no real bearing on P/V.
And on top of that, unless you specify the ICL where the cam will be installed you have added another error into the math of it.
The ONLY real way to know what your P/V clearance is is to degree the cam, install the valve train and measure it.
