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If I'm reading this right, the kit consists of a flex fuel sensor, processor + bluetooth transmitter, fuel lines, and wiring harness. The processor uses the flex fuel sensor to monitor the amount of E85 in the tank, and then increases or decreases the injector pulsewidth to maintain proper AFR. The kit is reliant on the knock sensor feedback and stock ECU to retard timing for lesser levels of E85, and a tune is required to advance timing beyond factory settings to achieve full benefit of E85. Is this correct?
Standalone ECU's usually blend two (or more) tables based on a flex fuel sensor's feedback. The first table is E85, so max injector pulsewidth and max timing advance. The second is either E50 or pump (depending on how the car will be used). The standalone ECU will actively interpolate between the two tables for flex fuel readings between the two tables.
So, a standalone ECU will provide optimal spark advance based on the flex fuel reading (with knock sensor feedback acting as a backup, for closed loop operation), while this kit will provide it solely based on knock sensor feedback. Can you confirm this?
My concerns would be first, there is a huge timing spread between MBT on E85 versus pump, and the requested spark advance would cause serious detonation if the knock sensors had a malfunction. The difference between 91 and 93 octane, versus 91 and 104/E85, is pretty large. My second concern is that fuel quality isn't constantly monitored by the stock ECU. Most OEM ECU's only check it right after startup or the cat warmup is complete, and maybe periodically after that (depends on the manufacturer, and I haven't looked at this for BMW in a while). The ECU essentially says "oh, you've got 93 octane fuel" and then targets the 93 octane table, fine tuning with knock sensor feedback. If one were to vary the ethanol content widely between tanks, it may not be picked up by the stock ECU, and either you won't get full benefit of E85, or the ECU will be constantly advancing timing until it detects the onset of detonation (then retarding it, then attempting to advance again... kinda risky IMHO). Lastly, you really need a dyno tune on C85 (commercial E85 that's exactly 85% ethanol) to take full advantage of flex fuel. Turbo cars often encounter MBT before knock when running E85, and a naturally aspirated car is even more likely to encounter MBT prior to knock, so a dyno tune is critical.
Otherwise, I can see it being a great product if you don't need it to be overly robust, and you fuel at the same location where ethanol content doesn't vary widely. If I were going to the track, I would ONLY run full commercial C85.
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