[Christ]

There have been engines designed specifically to alcohol, but the only ones I know of are the Ford 1.6MHO (Euro spec) and many aircraft enignes, as well as military "multifuel" engines.

Different fuels have a different "ideal" ratio, so to say that putting more fuel into a mix will decrease efficiency is a fallacy. If the ideal ratio were stoich (14.7:1) for alcohol AND gas, then you could say that's true, but it's not. (I'm not sure the ratio for alcohol, and it changes for different types of alcohol content).

Because of differences in burn rate, etc, the BTU value of different fuels doesn't necessarily determine the usable power output of the fuel unless other variables (engine type, design, etc) remain constant, and even then, there are variables beyond simple control such as heat soak that will determine output. Keep in mind that useful output is not the same as BHP. An engine that has a smoother torque application will accelerate faster and spend less energy as vibration, even with the same peak HP figure/location.