When does adding ethanol make sense?
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Instructor
Joined: Jul 2025
Posts: 132
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From: San Marcos CA
When does adding ethanol make sense?
Hello I have a fairly stock a4 c5: intake, LT headers, X pipe, axel back, 3.42 gears, “stage 2” transmission, and a dyno tune making ~360 rwhp. Does adding a flex fuel kit to run e85 make sence at all at this point in time on the build? I’ve heard from some people that ethanol only really makes a difference with boosted cars and others saying that it’s the best “cheap” mod for easy horsepower regardless of being boosted or not. What’s the consensus here?
No Hostility Be Happy
Joined: Aug 2018
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From: South Hill Wa
2022 C5 of the Year Finalist - Modified
2021 C5 of the Year Finalist - Modified
What most people don't tell you or neglect to tell you is how much MORE fuel it takes to make the same amount of power.
When you run E you will live at the gas station IMO.
There is a reason that you need more fuel system and injector to run E.
Do you even have pump E in commiefornia?
My opinion is, E really has no place in a street car that is a driver. Toy or racecar, sure.
When you run E you will live at the gas station IMO.
There is a reason that you need more fuel system and injector to run E.
Do you even have pump E in commiefornia?
My opinion is, E really has no place in a street car that is a driver. Toy or racecar, sure.
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
Melting Slicks
Joined: Dec 2018
Posts: 2,685
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From: Orange County, CA
There's a lot of E85 in CA. On 2 different cars back in the day (7-10 years ago) I daily drove in SoCal on E85 and didn't have to go more than 2 miles out of my way to fill up.
If we were talking about a more fuel efficient car, I would disagree. E85 on my old 2001 Audi A4 1.8T 4-cyl with upgraded turbo was a great setup worth a decent bit more power than our crap 91 octane. But on a hefty V8... different story.
If we were talking about a more fuel efficient car, I would disagree. E85 on my old 2001 Audi A4 1.8T 4-cyl with upgraded turbo was a great setup worth a decent bit more power than our crap 91 octane. But on a hefty V8... different story.
Running Guns & Moonshine
Joined: Aug 2001
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From: CT
I consider flex as a valid option and benefit for many who are supercharged if they have a strong tune and want to hit the track with more boost and timing. Absolutely valid, though other fuels are preferable for racing. E85 just offers convenience for those with nearby pumps.
On an NA engine I simply don't see the benefit. There is not as much power to be gained and the inconvenience washes that gain clear off the table. It isn't even much cheaper than gas around me now.
I ran one car for two weeks and maybe close to two thousand miles last year. My state having just ONE pump in the middle of it for E85 I was absolutely locked in on stopping there to and sometimes also on the way home from having fun. The only benefit I enjoyed was that on Friday and Saturday nights everyone running hot tunes and built cars was stopping at this pump which made it cool to see the Mexico builds heading out.
On an NA engine I simply don't see the benefit. There is not as much power to be gained and the inconvenience washes that gain clear off the table. It isn't even much cheaper than gas around me now.
I ran one car for two weeks and maybe close to two thousand miles last year. My state having just ONE pump in the middle of it for E85 I was absolutely locked in on stopping there to and sometimes also on the way home from having fun. The only benefit I enjoyed was that on Friday and Saturday nights everyone running hot tunes and built cars was stopping at this pump which made it cool to see the Mexico builds heading out.
