EGT change

[dougmattson]

I notice a 50 degree drop in egt's when I switched tanks from 93 octane unleaded no alcohol to 100LL. Running 100 rop, and did not change the throttle of mixture setting, I did not notice if the speed or rpm changed. Why is this?

[WingsOnWheels]

I'm not a chemical engineer: From my understanding, the lower octane fuels have a higher energy content. The addatives that increase octane also reduce the engery value of the fuel. This is why you always want to run the lowest octane fuel that meet the requirments of your engine design and operation.