Originally Posted by Martin@Tick

RezinTexas as always, great information! We also prefer checking springs and a dial indicator to show how much distance we have by pushing the valve into the piston while checking the dial indicator for clearance. Do this at least 20 degrees BTDC to 20 degrees ATDC or until your clearance begins to increase again. Also as Rezin Texas mentioned maximum valve lift has nothing to do with P to V as the piston is at BDC when the valve is at max lift. P to V issues occur when the piston is ATDC during overlap when the exhaust valve is closing and the intake valve is opening. Valve lift ATDC is what matters in terms of P to V and the more aggressive the lobe(meaning the faster it opens between .006" and .050" will really determine how much P to V is available considering free valve drop stays at a constant).

Second to none, like I told you today on the phone, you can run a 5.3 head on your motor and still have the exact same P to V as you did with your 317 heads since the valve size of the 5.3 heads is smaller and GM cast the chambers @61cc's. That along with having more valve drop on the 5.3 heads is why you can still retain factory P to V clearance. This is also why you can take a 64.7cc 243 head and place it on a LS1 motor that came with a 67.7cc head and still have the same P to V clearance as they both have the same valve drop.