[Formulas]

Not saying cam / lifters are the issue or not..... but when iam planning out engine build details the heads get ALOT of attention early on namely how much lift is desired and how much lift is possible

with the top of guides cut down for PC seals with a reasonable step to locate shims i cut the top of the guides down more to only have enough room accept a PC seal as low as possible+ a small extra margin... then insert intended valve / keepers / retainer using a weak spring that i got from my old damaged landscape pop up sprinkler heads ... see and record how much max travel there is then measure my seals protrusion over top of guide then do the math to come up with max valve travel before crunch then + a little safety margin then figure installed height of valve springs and go from there ..

thorough planning and alterations is the only way you will achieve KNOW max acceptable lift

a D'port head has to be massaged some to take .540-.560ish lift unless longer valves are used or more aggressive machining is done

store bought heads everything should be checked and verified or just plan to operate well under published data

food for thought like most ignition problems are blamed on the carb.