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Is Flex Fuel Right for You?



COBB has finally released their NexGen Flex Fuel for the 2015-2021 Subaru STi, but what does it do? How can it be beneficial to you? What can I do if this kit isn’t compatible with my car? I will cover the most asked questions about flex fuel, the uses for it, and what it means for the future of tuning with E85 and ethanol-based fuels.

Ethanol, more commonly referred to as E85, is an alternative fuel made from an alcohol mostly derived from corn. This ethanol is mixed with regular gasoline, typically 85% ethanol 15% gas.

While it was originally brought onto the market as a way to make the oil and gas industry more environmentally friendly the racing community quickly discovered the performance benefits of ethanol based fuels. E85 has some very beneficial properties for performance applications. It has an inherently high octane rating, which means it is resistant to pre-detonation, or “knock”. Ethanol also has cooling properties. It can keep temps down in your intake manifold and inside the cylinder. These factors combined allow you to run more aggressive timing and more boost which in turn will make more power. This is all done while staying within safe temperatures and knock thresholds. Long story short, you can make more power while keeping your engine healthy. This sounds great (it is), but there is a drawback. You can’t just go and put E85 in any car and expect results. E85 uses about 20% more fuel on average. Your car will need to be tuned to compensate for the extra fuel demand and to make that extra power.



How does the Flex Fuel kit work? Traditionally if you want to run E85 in your vehicle you would have 2 separate tunes; one for 93OCT pump gas, and one for E85 when you want to use one fuel or the other you will have to switch your tune over. The flex fuel takes away the hassle of switching tunes. Once your car is tuned with the flex fuel kit, it reads the amount of ethanol in your fuel and automatically adjusts your tune to compensate. This allows you to put in whichever fuel you like without worrying about how much of the other fuel is left in your tank or the actual ethanol content coming from the pump.



How does this benefit me? There are a few major benefits. First of which is ease of use. There is no input needed when you put E85 in your car. Everything is done automatically. Another use is with finding the actual ethanol % of your E85. The actual % of ethanol in fuel can vary greatly at the pump, anywhere from 50% up to 85%. This can cause problems with a typical ethanol tune if your car is tuned for 85% but you only get 50-60% you won’t get the performance you expect. The flex fuel kit can adjust all the way from E10-E100 allowing you to use a wide variety of fuels and not worry about testing your fuel before putting it in your car. Now you can have all the benefits of Ethanol based fuels without any of the headache of traditional testing and tune switching.



What do I do if I have a different year or model of Subaru? Don’ worry! COBB has announced that they will be releasing NexGen flex fuel kits for more models, including the DIT WRX and older WRX and STi. In the meantime, you can prepare your car for the flex fuel kit. Fuel system upgrades and power mods are usually needed in order to hit your goals. You can still do these upgrades before you get your hands on a flex fuel kit. You could either leave your car on a 93OCT tune until it arrives, or you can have a traditional 2 tune setup. Once the proper kit is released for your year/model you can just add the kit, get your car tuned for it and then you won’t have to worry about your ethanol content anymore!



The flex fuel kit in any of its iterations, is designed to allow you to take advantage of the benefits of ethanol-based fuels while making the needed adjustments automatically. This will let you spend more time enjoying your car and less time worrying about your ethanol content. Ethanol has many great qualities. It’s semi-renewable, more environmentally friendly, allows you to make more power, and keeps engine temps down. Flex fuel is a step in making E85 tuning more accessible to the automotive community.


Written by,

-Maya Thompson


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