I don't run E85 with the frequency you do, but I was playing around with it every other fill up until it got really cold out..The most aggressive mixture I ever ran was about E40, and the car threw the fuel mixture code, though it ran very strong and logged clean. I did notice AFRs were a tiny bit high with that mixture, but nothing crazy or in danger of lean out situations. Cold start wasn't quite as clean an operation, but I didn't have misfires/shuddering/distressingly long cranks. I've filled a mixture of 93 pump and E85 to E30 10 times or so, and never got any sort of code or issue. Mods are in sig, my car does not have flex fuel lines and is still on OE LPFP+HPFP, so fueling is 100% stock. All in all, my experience with modest E85 mixes was very positive, i'm not sure if I feel comfortable doing it every time I fill, but I don't have any serious issues to share. I'm interested to see how aggressive folks have taken it with stock fueling, any guesses as to when it gets too lean?
E88 N54 Alpinweiss/Coral Red/Motiv HTA 3586r Tial .82AR/Motiv Port Fuel/Meisterschaft Race/Berk Resonated/ER CP/Synapse/VRSF FMIC/Rob Beck PCV Valve + Cap/ST Coilovers/M3 FCA + Tension Rods/M3 Subframe Bushings/M3 FSB/AA Strutbrace/DINAN Camber Plates/Apex ARC-8/Project Kics/VAC Hubs/Rogue Transmission Mounts/Alpina TCU Flash/Icarbon/Kerscher/BMW Performance