To clarify things, the N54 cannot run any form of E85 mixture using stock
The guys who run E85 mixtures have tunes
to up fueling needs up to an E50 content. Power is made from allowing it to run more boost, cleaning up ignition corrections, or advancing ignition in some cases. No other upgrades are needed. I ran an E50 mixture running over 400rwhp/tq for a good year, using methanol on top to cool IAT's only; I would otherwise max at 375rwhp range with just a tune + methanol (to give an idea how much an E50 setup helps with power) No hiccups, no issue's, and I feel was a reliable source of power. But N54 guys also have DI.
Any mixture beyond E50 requires either a 1) Walbro inline booster ($100 or so) or 2) upgraded Walbro LPFP ($300).
Another plus I see running either straight E85 or an E85 mixture is that it cleans up exhaust gas smells, perfect for anyone who wants to run test pipes+X-pipes (catless) and worry about gas smells, it almost eliminates it
I'm thinking of picking me up a Procede Piggyback system that allows logging of a/r ratio's, adjustments of fueling, ignition timing control advancement + more through a laptop to see if I can "tune" things for an E50 mixture. Procede is well-known in the N54 world and have e85 tunes for them. I'd like to go with a real tune/flash system, but none seems to offer the ability to log the car, which I'm OCD about, so Procede may be on my list.