Quote:
Originally Posted by qtwre
Won't a turbo just spin faster to hit the same boost target, regardless of elevation? Oh, but then I guess intake temperatures would go up, losing power.
Touche.
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There's a little more to it that seems to be forgotten when people talk about turbos at altitude...
Quite often the boost control setup is designed for a target above atmospheric pressure, and isn't set up to read absolute pressure. (this will be the case with a manual boost controller) What happens in this case is your turbo spins a little faster to create the (same as sea level) pressure to overcome the spring, but atmospheric pressure is lower, and so your absolute pressure at the manifold is lower as well. It's not as big a difference as you have with a supercharger. but it's there.
if your boost control is set up to hit a specific absolute pressure in the manifold, using a map sensor and controlled by the ecu or some other electronic device, then this isn't an issue and your car should be capable of VERY similar horespower numbers at elevation and at sea level. like what Mike mentioned about the BMWs.