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How Does Ethanol Affect Gas Mileage?

You don’t have to go far to hear folks complaining about how the current level of ethanol content in unleaded gasoline has affected the gas mileage in their vehicles. Today’s gasoline contains approximately ten percent ethanol, for the most part, and is referred to as E10. Finding “ethanol-free” gasoline at a common service station has become increasingly rare, at best.

Ethanol contains approximately 33 percent less energy than gasoline. If you were to run 100 percent ethanol (E100) in your vehicle, you’d expect to take a 33% hit to gas mileage.* (Theoretically, since you can’t legally run 100% ethanol.) With E10, it’s a 3.33% penalty. Seeing that you can’t buy E0, there’s not much you can do about it.

At some point, we hope to perform dyno and real-world tests to document the drop in gas mileage. With “pure” pump gas nearly impossible to find, we’ll likely have to buy expensive street-legal racing fuel.

The game is changing with E85 (85% ethanol) in FlexFuel-capable vehicles. While older FlexFuel vehicles show significantly lower gas mileage with E85, some newer engines are optimized to run on E85. We tested E85 vs E10 in a FlexFuel Buick Regal Turbo and experienced a 12% drop in gas mileage.

Ethanol is an excellent fuel in the right applications. While it contains less energy, it packs more octane, which allows for higher horsepower output. This makes it an excellent choice for high-performance engines. In addition, it also burns at a cooler temperature and does away with carbon deposits.

Racers are taking the lead with ethanol, as they seek to extract more horsepower at a lower cost per gallon than conventional racing gas. At X Games 17, at least two Rallycross cars ran ethanol race fuel, with Stephan Verdier and Jimmy Keeney both running ethanol in their AWD Subaru STis against conventionally-fueled competition. Andrew Comrie-Picard won two bronze medals at X Games 16, running ethanol in his Mitsubishi EVO.

The development of high-output ethanol-fueled engines isn’t restricted to the race track. The Ricardo Ethanol Boost Direct Injection (EBDI) engine produces 900 NM of Torque from a twin-turbo V6.

* Source: U.S. Energy Information Administration: How much ethanol is in gasoline and how does it affect fuel economy?

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1 comment so far ↓

#1 Tyler Lipa on 08.11.11 at 9:27 pm

Awesome write-up I’m actually going to be getting a Buick Regal Turbo soon for a long term tester and I am excited to see what kind of fuel economy I can get on E85. There are quite a few stations here in Indiana. I’m quite excited since it will be my first experience with an alternate fuel engine.

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