Many years ago we race in Denver a number of times for Divisional Meets. The high altitude made the tune up a challenge, I do remember that!!!! Can't comment on the compression thing as whenever we were out there the car was running on race gas.... It's hard to get enough air in the engine to make it run correctly at altitude.... Bandimere used to have a "tune up reccomendations for the Mile High" section on their website, might want to check there....