Quote:
Originally Posted by SeanWRT
F87source , Raymondo and TTFS are correct.
DME responds a little differently car by car, even the same platform. In early 2017, Wang my friend, the then N55 1/4 mile record setter (I have a thread dynoing his car), see zero gain from E40.
My abuse M2 (installed everything except for big turbo) struggles above E50, but the gain above 30 is very marginal.
Ethanol improves octane no doubt about it, but it also messes up with AFR which in a way can affect power. It's complicated, there is no definitive theory on it. For example, outside of BMW, GTR is known for being happy with E85 but it is not happy with E95-100.
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You're on a stock HPFP which makes the comparison different, i'm not sure how you even got to E50 on the stock HPFP. In regards to your friend, it's a misconception that adding more ethanol increases power, that's not how it works.... You increase ethanol content to increase your octane rating, that way you can run more timing and boost. You don't add more ethanol and expect power ratings to go up that's simply not how it works or what I was implying, so you may have misinterpreted my statement. What I asked OP was why he didn't run more ethanol to push the PS2 to the max, was it because the XDI pump was tapped out? If he was happy with 4XXwhp then of course you don't need to add more ethanol content, that would be done for no benefit except putting more strain on your fuel system. But if you wanted to max out PS2 then you have no choice in this scenario.
Also when you tune a car you're not looking at how the DME responds, that's just looking at stock fuel adaptations which shouldn't matter if you tune the car to match your fuel requirements. If all you cared about was how the DME responds then your tuner isn't making any meaningful adjustments to make your car run right.
I couldn't push anywhere near the limits of the PS2 on my m235i on anything less than E55. Of course your AFR's will be leaner on E85 because of the oxygen content in the fuel, a tuner can adjust for this based on E content used. There are a bunch of tuning documents online elaborating this. The only way you affect power negatively using E85 is on a garbage tune, if you correct for the AFR's you'll be fine. I've used E85 all the way to E98 on all of my previous cars with protunes and zero issues. Albeit anything over 85% ethanol from what I have heard is not optimal because ethanol lacks the lubricity of gasoline.