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Engine power lose at extreme altitude?

('14-'18) 
2K views 5 replies 4 participants last post by  FXTerrific 
#1 ·
I was at 5200m/17060ft earlier (without my Forester unfortunately), and was wondering how much HP I would've had there. Some calculation I found online ended up below zero so I guess they aren't meant for really high places.

Anyone have a reliable calculation for turbo and NA motors?
 
#3 ·
I live near the Mile High City (Denver, Colorado).

I have driven turbo cars since 1990 both at near sea level (Kansas City) and have learned this:

Be it tires or intake manifolds, air-pressure gauges can (can only) read the difference in PSI between the outside (ambient) and internal air.

Thus, if you filled a tire to 35 PSI in Denver, then magically teleported it (and the same gauge) to Kansas City, the PSI would read lower in KC due to the higher ambient pressure of the outside air.

The turbo boost gauge in your car will read the same maximum PSI in Denver as KC because the turbo design itself can only deliver so many difference-PSI (ambient vs intake) regardless of altitude.

Bottom line: The higher you go in feet, the less HP you get, turbo or not. Exactly how much less depends on your car, the fuel, the air temperature and humidity.

Here's more explanation:

exterior ballistics
 
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