Thursday, Jun 14, 2007 at 23:25
Signman,
As altitude increases, the air gets less dense (for a number of reasons). Also the oxygen saturation of the air decreases.
This is mainly evident in a piston/non-turbo plane where power is a measure of manifold pressure in inches of mercury. At sea level, or standard atmosperic pressure of 1013 hpa, with the engine idling, MAP (manifold pressure) will read just under 29" of murcury. At full throttle, 27" of murcury: APPROX
At 10000 feet, with full throttle, the same engine may only recieve 15-19" of mercury MAP. this means that a 300 bhp engine at sea level, will only be producing approx 130-140 bhp at altitude.
The same will happen to any internal combustion engine, diesel or petrol, turbo or non-turbo.
The turbo being only driven by exhaust gasses, can only spin so fast, therefore cannot compensate for the loss in air density, and will spin at roughly the same speed, but produce less boost as it will compressing less dense air.
Turbo planes get around this by usind a turbo to MAINTAIN rated power. Meaning at sea level the waste
gate is fully open, and no boost is provided. As the plane climbs, the air gets les dense, that waste
gate begins to close, and boost is increased to MAINTAIN sea level power.
So the answer to the question is,
Any increase in altitude will decrease air density and decrease boost, and therefore horsepower.
Making the air colder, ie intercooling more etc, will reduce the serverity of the loss in power, but not to a noticable extent.
Hope this answers ya question pal,
Cheers
Wayne-o
AnswerID:
246931