[SampleMan]

A 50 or 75 percent improvement would probably put a gas engine beyond its theoretical max efficiency.

No, the theoretical limit is the energy in the fuel, which is about 275 mpg. The problem is that most of the energy is wasted producting heat.

[valkyry1]

No, the theoretical limit is the energy in the fuel, which is about 275 mpg. The problem is that most of the energy is wasted producting heat

Thats why he referred to the theoretical max efficiency of the ic gas engine. The fuel has to combust so how will it get around the problem that most of the energy is wasted in heat?