Flex Fuel and E85: What They Are and Whether They Suit You

What is E85?

E85 is a blend of ethanol and gasoline. Despite the name, it is not always 85% ethanol. According to the US Department of Energy, E85 can contain anywhere from 51% to 83% ethanol, depending on where you are and the time of year. Winter blends usually have less ethanol so cars start more easily in the cold.

That variation matters for tuning, and we will come back to it below.

Normal pump gas in the US already contains some ethanol, usually up to 10%. E85 just has a lot more.

Why does E85 help performance?

The main reason is knock resistance. Knock is when fuel in the engine burns unevenly and too early, which can damage the engine. Octane is the rating that tells you how well a fuel resists knock. Ethanol has a much higher octane rating than gasoline, so an engine running on E85 is less likely to knock.

That gives a tuner more room to work. With less risk of knock, the tune can safely use more boost and more aggressive spark timing. Ethanol also cools the air inside the engine as it evaporates, which helps too.

On turbocharged cars especially, the difference between premium gas and E85 can be significant. How much depends entirely on the car and its parts.

What are the downsides?

We think it is important to be straight about these.

You will use more fuel. E85 contains less energy per gallon than gasoline. The Department of Energy says E85 with 83% ethanol has about 27% less energy per gallon, and flex fuel vehicles get roughly 15% to 27% fewer miles per gallon on it. Expect to fill up more often.

It is not at every gas station. E85 is sold at a limited number of stations in Georgia, and they are not spread evenly around metro Atlanta. Before you commit, check how close the nearest pumps are to your home and your usual drives. The Department of Energy's Alternative Fuels Station Locator (afdc.energy.gov/stations) is a good place to start.

The car usually needs supporting parts. Because the engine needs much more E85 than gasoline to make the same power, the factory fuel system may not keep up. Depending on the car, that can mean upgraded fuel pumps or injectors. Some cars can run a partial blend, like E30 to E50, on the factory fuel system, but full E85 usually needs more.

The blend changes. Since the ethanol content of E85 changes by season and station, a tune written for one exact blend can be wrong for the next tank. That is the problem flex fuel solves.

What is a flex fuel kit?

A flex fuel kit adds an ethanol content sensor to the fuel line. The sensor measures how much ethanol is actually in the fuel and reports it to the engine computer in real time.

With a flex fuel tune, the engine computer uses that reading to adjust fuel and timing automatically. So you can fill up with premium, E85, or any mix, and the car adapts. If you are on a road trip and cannot find E85, you just fill up with premium and drive normally, with the power level that premium allows.

That flexibility is why many people choose a flex fuel setup over a tune that only works on E85.

Is E85 bad for my car?

Ethanol can affect some rubber and plastic fuel system parts that were not designed for it, and it can attract moisture if a car sits for a long time. Cars built as flex fuel vehicles from the factory have parts designed for it. For a performance car, part of planning an E85 setup is checking that the fuel system parts are suitable. We will go through that with you before recommending it.

Is E85 right for me?

E85 tends to suit you if:

• your car is turbocharged and you want more than gasoline alone allows,
• you have reliable access to E85 near home or work, and
• you do not mind spending more on fuel per mile.

It is probably not worth it if you mainly want better fuel economy, drive long distances away from E85 stations, or want the simplest possible setup.

We offer flex fuel and E85 options as part of our tuning work. We will tell you whether your car is a good candidate and what parts it would need.

Tell us your car and where you usually fill up, and we will quote a flex fuel or E85 setup that makes sense for it.