Originally Posted by Zero_to_69
The industry standard uses 0.006" as a zero lash point.
I think this is to ensure all of the play has been eliminated through the
valve train when setting hydraulic lifters.
If the camshafts are to be compared, the must be a defined start and end
point (hence the 0.006" and 0.050" references).
Someone please confirm.
IMO, there is really no "Industry Standard" for measuring total duration.
"Advertised Duration" used by some cam companies may use .006 valve lift point. Engine Analyzer PRO uses .003 valve lift to quote total duration. They say that this corresponds quite closely to many cam companies' "Advertised Durations".
In my mind, "Lash Point" when applied to solid lifter systems, is the point at which all the lash has been taken up by the opening/closing ramps on the cam lobes, and the lifter/pushrod/rocker/valve is just starting to move. GM applies the term to both solid and hydraulic cams, but they also use very long hydraulic ramps, especially on street cams.
There are so many variables in the ramps (not the "flank" or portion of the lobe that does the majority of the lifting) of OEM and aftermarket cams that two cams with 220 degree @ .050 duration might have "Advertised" or "Total" durations from 270 to over 320 degrees.
For example, the Gen V 502 hydraulic flat cam (14096209) has 220 deg @.050 duration and 328 degrees at lash point. The old LS-6 mechanical (solid) flat (3904362) has 242 deg @ .050 and 307 degrees at lash point on the intake with .024 lash. The exhaust is also 242 @ .050, with 298 at lash point and .028 lash. The .004 difference in lash looks like it makes about 4.5 degrees difference on both opening and closing, if one assumes opening and closing ramps are similar.
"Curiouser and curiouser." Alice must have been into cams!