Your question would seem to be quite a tricky one at first reading.

I'm no expert, but it seems to me that we should consider your question " at its extreme".

If, instead of ascending to a mere 10.000 feet, we ascended to say, 100,000 feet, what would we expect?

I would guess that, the air being so thin, that motor would be wheezing out its very last gasps. Where each cylinder-full of air was weighing only a tiny fraction of its sea-level weight, the motor would be able to burn only a very small amount of fuel. Yes, the prop would be offering little resistance, but the engines internal losses would remain constant, so the power available for useful work would be less than was found at sea-level.


If I remember correctly, Piper specify for their PA-28 that, at 6000 feet, the engine is capable of producing only 75% of its rated output. This engine is fitted with a mixture control, but is normally-aspirated.

Springer