[mr0077]

From memory, the typical EGTs on aircraft were about 1150 degrees F at 75% rated power, but someone out there surely flies recips regularly and can chime in. I think idle EGT should be a lot lower (400-500 F?) simply because of the difference in volume of BTUs generated at idle v. load/cruise, as well as the timing, mixture, etc.

BTW, I would think that, all things equal, an engine that was more efficient (such as your 12.5:1 motor) would have lower EGTs than a less efficient motor (such as your 9.8:1 motor), as it would convert more of the BTUs from combustion process into mechanical energy, with less heat going to waste out the exhaust...similar to a turbo, converting waste exhaust heat into pressure+mechanical energy at the flywheel.