I read two articles about alternate methods of measuring piston/valve clearance by subtracting the intake valve opening (distance off the seat) at [TDC-0degrees] from the valve drop. This proceedure is outlined on ISKY's website if interested.

I have always thought valve drop was the measured distance the valve travels from the seat to contact the piston sitting at TDC. Another article talked about the valve drop being from the valve seat to a flat surface without being mounted on the motor. In my example of course I need to know the distance when mounted since it accounts for the negative deck height of the piston comming out of the hole (.008-.010 on most LS engines) and the thickness of the gaskets used and also accounting for any milling. The second method only acounts for milling.

Jason at Texas speed was kind enough to note the valve drop for his install being .140" on a 64cc milled L92 head which is about .170" for a stock head, unmilled, with stock gaskets, assuming the first methood of calculating. While cam specs can be off and actaully measuring the distance during the overlap period is best for final testing, the purpose of this quick and dirty calculation is to run the specs on a calcualtor and check to see what doesnt fit before you have a cam ground, and mounted in the motor.

Any takers?