I found some information from AmericanEnergyIndependence.com:
Because of the compression limitation required to prevent “engine knock”, a typical gasoline engine can only deliver about 25% efficiency — only 25% of the BTU's in a gallon of gasoline are converted to mechanical energy that turns the wheels of the car, the other 75% is lost in waste heat.
An Alcohol Engine can deliver about 40% efficiency — 40% of the BTU's in a gallon of ethanol powering an Alcohol Engine will produce mechanical energy that turns the wheels of the car.
*Note that efficiency refers not to fuel efficiency, but to efficiency per BTU.
0.40 / 0.25 = 1.6
In other words, the amount of power you can gain from the same BTU's would be aproximately 1.6 times greater.
Courtesy of Pᴀᴜʟsᴛᴇʀ2: Note that you also have to put in more fuel to get the same number of BTU's. (Pure ethanol has an energy content of 84,530 BTU/gal, whereas standard gasoline has around 120,388 BTU/gal.)
This means that you get approximately the same power per gallon, but because the Ethanol supports a higher compression ratio, you can send more gallons through the engine. The end result is that you get the same amount of power per gallon, but you get a 60% increase in your power per minute.