Jeez - the current EPA limit on ethanol concentration (by volume) for pump gasoline is 10 percent, so any oxygenated gasoline dispensed from a gas station as motor fuel for on-road vehicles is no less than 90 percent gasoline. An automtive engine designed for gasoline or "gasohol" with a small quantity of ethanol will not operate on a high concentration of ethanol due to the substantially different A/F ratio, which would require considerably higher mass/volume flow of fuel.

Octane rating is a measure of resistance to detonation. That's it! It doesn't burn "slower" in the absence of detonation. If an engine operates without detonation on a given octane, then additional octane DOES NOTHING!!!

Ethanol is an octane enhancer, but has less energy density, so base stock gasoline oxygenated with ethanol has lower octane than a base stock not intended for oxygenate addition. Ethanol brings a base stock intended for oxygenation up to the pump posted octane. Also, ten percent ethanol reduces the energy content by about 3 percent so fuel consumption is increased by about a like amount.

Duke