NO, NO....at high altitude you must raise compression ratio, not reduce it. There is several ways, either raise nitro contents, or use a thinner shim, or both. That is why I'm asking what shim is he using right now. And plug will have to be determined later, because it will affect ignition timing. High altitude (less air density)tuning is completely different than sea level (higher air density), so carburation will definetively will be leaner, but it has to be done step by step stating from base carburation. Here in Peru we've even raced at 3,300 mts. Now the kings in high altitude tuning are Mexican drivers.

AFM