Energy/volume is irrelevant (at these levels). What really matters is the usable energy coming out the engine compared to the engine coming in. Because of its higher octane, ethanol could in principle be run in ICUs with much higher compression ratios than engines designed for gasoline use have, giving higher efficiency (like diesel engines have higher efficiencies). The problem is that no engines actually are tuned for maximum ethanol efficiency, since that makes them unusable with gasoline. (Turbocharging somewhat offsets this, which is why I assume the grandparent specified this, but only partially.)