Manifold pressure - Altitude effects

[ft]

italia458,
what hot gasses?

In a naturally aspirated engine, you have expansion affecting the temperature in the manifold. In a charged engine, you (usually) have compression. What's more 'normal', as far as temperature in the manifold goes?

In a constant volume, n is directly proportional to density.

I showed that the ideal gas law applies to the standard atmosphere as used by you, which was my intention. Knowing this, and assuming that the temperature drop or increase you see due to expansion or compression from ambient to MAP is also in accordance with the ideal gas law means the hypothesis about the density/pressure interrelationship being the reason for the lower required MAP is not an explanation for the observed phenomenon. You will end up with the same temperature in the manifold regardless of ambient.

(Disclaimer still applies though.)

As for back pressure, I can't really see that proof is needed for the engine using power when it is pumping air against a pressure. I'm not really interested in debating whether it is the explanation or not. Dig up a few more references for comparison?

Standing by for additional explanations.

Also, you're quoting Aerodynamics for Naval Aviators out of context.

Edit: Lower exhaust back pressure also means more complete evacuation, which for a given MAP means you get more of a charge into the combustion chambers = more BHP.

Cheers,
Fred