How much more compression do you need (or can you run) VS how high you are asumeing you fix your jetting for the change so the elevation is the only real differance? Same octane fuel of course.

multiply by 10s for 1000 ft

up here in central oregon (3600 ft) i add about a half point or so. i reckon there's prolly a formula, but i don't recall seeing one. i'm thinkin' it would be a simple matter of determining your air pressure. we average ~9% less dense than sea level.

I would think that the cam would make a bigger impact, a later closing point. Cyl. pressure, Over static comp.

http://www.rbracing-rsr.com/compression.htm

Try this and just input 0 for the PSI number. It will show you what happens at different altitudes.

Thats a handy calculator

My 11.5 is going to be about 10.9 at my 3000ft altitude

It worked good for me figuring what to do with my blower at the elevation I am at.

For some brain exercise, this is a good study on the effects of elevation.

Intended application of this report was for aircraft, but there is good applicable info.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091074_1993091074.pdf