wreckdiver1321
Overlander
The octane is higher, but the energy density is less.
This. Remember, higher octane does not equal more power.
The higher the octane, the more compression it takes for combustion. This is why racing cars run high octane fuel. Their engines are high compression, which means more power. But in order to get peak performance you need the explosion to occur as close to TDC as possible. Lower octane gas will ignite earlier (known as "pinging" - very bad for an engine), thus losing efficiency.
If you have a vehicle tuned for regular unleaded and put premium in it, you'll actually decrease performance, because the fuel is harder to ignite and when it does, it doesn't burn fully. High octane + low compression = inefficient.
As far as ethanol is concerned, it does have a higher octane rating, but the amount of energy it contains is noticeably less, meaning it's less explosive. It doesn't create the same amount of force when combusted under pressure, so it doesn't push against the pistons with as much force as gasoline does. That makes it less efficient. A less efficient engine burns more fuel because it needs to work harder to move the load.