Valve Clearance

[JayP177@aol.com]

Anybody know why the valve lash varies from one cam manufacturer to another
when the duration is about the same. Some use .010 clearance and another will
use .024".
If the difference is due to the takeup ramp design then why does the ramp
design differ. Also, how much can you vary the valve clearance from the cam
specs to vary the duration and how much total duration is increased for each
.001  of decrease in clearance.
65B