How much horsepower do you lose at a higher altitude?

Question

I'm sure there's a complicated formula for it - but I just drove my uncle's 2008 Corvette (430hp stock at sea level). About how much would it run at in Colorado? Denver is at 5,280 feet, and the canyons I was driving in were between 7-9,000 feet. Is there an approximate percentage you loose with every 1000 ft it increases? Thanks!

Answer 1

Denver is said to lose between 7%-12%, way to many factors to get exact answer.

Answer 2

http://www.anycalculator.com/enginehorsepower.htm

Even though altitude is a matter of geography, not weather, elevation plays the biggest single role in the horsepower/performance equation. For every 1000 feet you climb above sea level, there is a reduction in air density of approximately 4.5 percent, according to Marcellis. So, for every 1000-foot gain in altitude, there is a corresponding loss of horsepower, which means our 200 hp outboard gives up 9 ponies.