ORIGINAL: Sport_Pilot
ORIGINAL: triumphman49
do you also have a hard time understanding that a .40 diesel will turn a bigger prop faster than a glow .40?
Not if you get a cold enough plug on the glow engine. It is the fact that you are canging timing when changing the compression that does this. The timing for glow is from changing the glow plug, so unless you use spark ignition this is difficult to get the right timing. With complet timing adjustability then methanol will have more power and torque than gas or diesel fuel. But not very efficiently.
Glow engines also can adjust the torque from ignition timing by varying the nitro content in the fuel as everybody knows. So, compression ratio, glow plug temp, and nitro content all affect timing, which affects torque, which finally affects power. But don't ask me for numbers, this is just qualitative.
Also remember that propeller efficiency changes with engine speed. A slower turning big prop would more likely give higher thrust than a small fast spinning prop. So in the end, if the gas engine is designed and tuned just right, while turning a bigger prop at slower speed, can potentially produce greater thrust. And ultimately, that is what matters when flying.