E85 makes more power, but is generally harder to find, and it requires a custom pcm file. You should also note that you cannot freely switch back and forth, as the mix in the tank will never be able to settle, and you will risk hurting your engine. If you do plan to switch fuels, you need to run the tank as empty as possible, and remember that you’ll never be able to get every drip out of the tank, so your fuel trims will be all over until you can find and run a consistent E85. Another important note to keep in mind is that E85 also varies from tank to tank, and season to season, so it’s definitely a good idea to keep an eye on your tune with an Aeroforce gauge. Running E85 will also take a massive fuel system, such as large fuel injectors, a big fuel pump, a fuel pump rewire kit, and possibly raised voltage. But if you follow the rules and do everything right, you will get a lot more power, and a pleasant popcorn smell as an added bonus!
I’ll leave you with this bit of conversation about ethanol levels in E85 fuel.
“I called J&H oil (our local gas station supplier) about purchasing a 55 gallon drum of E85. After about 4 or 5 transfers I ended up talking to the guy that actually is in charge of the fuels.
Here is how E”85” is sold:
June/July it is E85
Aug/mid Sept it is E80
Mid Sept/Oct it is E75
I am assuming that this is only accurate for our part of Michigan.
Gas stations are only legally required for their E”85″ to be 70% ethanol (e70) to be called “e85”.” -Tim 10/18/2010