My FE/Performance Project

[theholycow]

Originally Posted by pgfpro

The turbine performance increases as the pressure drop between the inlet and outlet increases, i.e. when more exhaust gas is dammed upstream of the turbine as a result of a higher engine speed, or in the case of an exhaust gas temperature rise due to higher exhaust gas energy.

Ok, I can imagine that heat is conducted out of the exhaust gas through the turbo, so it's cooler and denser on the output side, which could conceivably result in higher pressure on the input side than the output side...and the more dense exhaust gas now requires more energy behind it to get it through the rest of the exhaust system (unless it's a tailpipe turbo).

So far, that gets us to where it is using exhaust energy to shove more air (and therefore fuel) into the engine, reducing pumping loss on the intake but increasing it on the exhaust. At most, if it was a 100% efficient machine, it would seem to come out even.

Erik's explanation makes more sense to me, though.