Quote:
Originally Posted by jcge
John D - camgrinder
re 906 profile
Perhaps its range of applications from the factory is a testimony to the those long clearance ramps and the range of impact to duration via simple lash adjustment.
906
911R
908/917 (I assume it underwent some geometric rearrangement for bucket followers)
and others no doubt
Any thoughts or further info on this profile - maybe worthy of a thread in it's own right.
John
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you could go tighter than .004" cold, but not looser. If you have more than .012" hot on most profiles, the valve seating velocity gets too high and you can bounce the valve off the seat. The exception is that 315-300 Walt has in his engine. Those clearance ramps are higher, and need more lash. .006"-.008" cold.
I think its more to do with available valve springs at the time they designed the 906 profile. They wanted reliability at high rpm vs. HP from the looks of the profile. Very conservative profile.