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      01-17-2020, 09:36 AM   #7
Second Lieutenant
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Drives: '19 Audi RS5 Sportback
Join Date: May 2019
Location: Erie, CO

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Originally Posted by jpy1980 View Post
I wanna do this because i have crappy ACN 91 octane. I tried using a couple of gallons of 100 octane but at $10/gallon, it was pricey.

Would making equivalent to e20 be as beneficial as a couple of gallons of 100 octane?
On previous cars, I've run full E85 and flex fuel setups to varying degrees. In my experience, unless you have a proper flex fuel kit installed to measure the E85 mixture and calibrate the tune accordingly, you're just adding more hassle and complexity for little to no gain.

In theory, adding 2-3 gallons of E85 at every fill up will boost your octane by 1-2. However, without a proper flex fuel kit/tune, adding a couple gallons of E85 in at each fill up will lead to you truly having no idea what your fuel mixture is on an ongoing basis, unless you run the tank completely dry before every single fill up. Which, let's be honest, you're not going to do that.

I highly suggest that you don't bother unless you get a proper flex fuel tune and have some sort of gauge to monitor your fuel mixture in real time.

If you wan't more power, flash a proper tune designed for your fuel type and call it a day.
'19 Audi RS5 Sportback

F80 ///M3 | Mineral Gray Metallic | 6MT