John, Isky's advice was good 50 years ago, when cam-grinding technology was in the stone age. Now, with ultra-precision computerized machine tools, it's as obsolete as kerosene headlights and hand-cranked engines, sort of like manual transmissions.
I remember the little paperback book written by Ed Iskenderian in the early 1950's "Top Tuner's Tips", where the concept of degreeing a cam by altering clearance for individual valves to assure each valve got the exact same duration was suggested. I also watched my father use that method on flathead Ford race engines, using Johnson adjustable tappets, and then brazing the adjusting screws in place so they wouldn't change position.
Increasing clearance effectively shortens valve duration, which, in theory, allows for a longer compression stroke. The same result can be achieved by installing a slightly shorter-duration cam , such as using a Comp Cams 260-degree item instead of a slightly more radical 268. The idea of influencing compression pressure with a minor adjustment of valve lash looks good on paper, but I challenge anyone here to show me a measurable difference on a dyno. I'll even provide the dyno, if anyone is up for the challenge!
Jerry
