Rhoads Lifters On Solid Lifter Cam - Setting Valve Lash

66jim said

Yes this is true on elevation, the driving I described is between approx 1000 and 2000ft not huge but noticeable. I have checked compression at 1000 ft and 2000ft
155/160 and vacuum 19/20+. Then driving down to 400ft increased to 21hg idle.

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1000-2000' is not enough to make me think the engine has an issue with the same compression range. Used to drive a high compression engine from 1000' to 2200' every day. I have noticed the same changes going from 1500' to to sea level, and a bit more tendency to detonate. And going to 5000' is indeed a big change..... "What's gone wrong with my motor?!?" LOL