I grew up in Colorado (mountains west of Denver, ~9000' elevation) and raced out there for quite a few years...what was interesting is on a normal hot summer day, the density altitude at Bandimere Speedway (5800' elevation) would be well over 9000'....cars were slow, unless you bring your own atmosphere...I preferred to keep mine stored in a blue bottle. My old 360 motor, would run 13.8 NA, but would drop to 11.0 on a 180 shot. That same motor when I moved to Indiana ran 12.4 NA (850' elevation, DA in the probably in the 3000' range (typical summer air guesstimate)).
My point is, air density makes a huge difference. Car ran over a second faster at lower altitude.
