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Ounce for ounce ethanol contains less energy than gasoline. At the same time ethanol can have a much higher octane rating than gasoline. The paradox is an engine designed to run on lower octane gasoline will not burn ethanol very efficiently. This means in general that more ethanol must be burned to return the same energy as gasoline from such an engine. Conversely a high compression or turbocharged engine designed to extract every bit of energy from ethanol will not run very well at all on low octane gasoline. Many of the existing Flex Fuel vehicles actually experience a decrease in fuel economy when running E85 over straight gasoline. While this problem may be offset by the lower pump cost of E85 the benefit of burning more fuel to achieve an environmental end is somewhat questionable.
On the plus side engines and vehicles exist and are on the way that burn E85 at maximum efficiency. Through use of turbochargers and other means, an engine specifically designed to run on E85 or even straight ethanol can return a great deal of energy indeed. Drag and circle track racers have known about this fact for a long time. Racers have been burning up ethanol's chemical cousin methanol and setting records for many years. In fact the Indy Racing League is making the switch over to E85 this coming year. Other racing organizations are considering the switch as well. Alternative fuels, such as E85, need not be boring! A vehicle specifically designed to run only E85 or 100 percent ethanol can solve the efficiency problem but cannot get around a lack of distribution. In this sense a Flexible Fuel Vehicle is indeed flexible, for it can run on E85 or gasoline.