E73 isn’t bad at all most winder blends end up being E60. But if you do 7 gallons of 93 and add 4 gallons of E70 your still at 97 octane. So not too bad. Better than what your working with right now.
The fact that the e- content is lower might be a good place to start.
E40 no problem at all in my experience. It goes faster. I have run the car with up to e85 even in winter. The fuel consumption goes up as it should. I havent pushed the car that hard with only e85 but yes in my experience with no tune there is probably little to be gained from it (for the reasons mentioned: octane more fuel needed to be pumped in). At somewhere between e40 and e50 you start getting check engine light at some point bank 2 oxygen sensor.
No issues at all though thus far.
Hey TontoLoid, welcome and thanks for sharing your experiences, A few questions naturally as I embark on this myself once life goes back to being somewhat normal.
Have you done any logging to look at fuel trims by any chance? The BTU of E85 is less than that of gasoline so you should need quite a bit more to make the same power, hence your consumption rate going way up.
The check engine light is probably because the fuel system can’t push enough fuel within the parameters dictated by the ECU. May be out of range so to speak.
In winter, the actual ethanol content fluctuates and goes down. In some areas the content will drop down to E60. My “winter” blend registered at E72 and I’m waiting for the summer blend of E85 before experimenting as I don’t want to constantly sample and have to recalculate ratios to achieve E40.
On the fuel injector front, I know lots of the RS3 guys are now having injector issues due to using straight E85. I just replaced mine and I don’t want to do it again any time soon as it isn’t cheap! I’ll probably stick with E40 and a tune.
Do you by chance ever add any additives like Techron to the tank to help clean the ethanol residue? They generally mix the ethanol with 85 octane no detergent package gas (crappy gas in other words!). My plan was to use the flex fuel pump to mitigate some of this and adding Techron every other tank or so.
Thanks! Happy to be here.
Havent analyzed things properly would certainly if i wasnt in one of the few countries not in lockdown.
Build up on the injectors was said years ago to be due to ethanol not being compatible with some additive in the gasoline to prevent it. Therefore the cleaner was added with the fuel. It is some kind of gunk being formed (not carbon). The cure was said to be a tank of regular gasoline every 5 full tanks or similarly often.
As for the ethanol content I have experienced no calibration issues. Who know maybe pushing the set button per the manual will speed up the calibration but I am fairly sure that by the time you have warmed up the car you’ll be golden.
As the exhaust oxygen sensors, due to e85 containing more oxygen, will continue pumping in gas you will never run lean. I have never ran rich either. If anything my fuel consumption has been slightly better without less power only thing I have experienced is more power. Especially in hot conditions with slightly dense air you should see an improvement vs gas. The typical scenario of failing injectors on cars like ours must be driving it hard perhaps or bad gas. Mine are perfectly fine after varying between various ratios of E, 95,98,100,102 octane. Havent been putting in premium gas that often although doing it now and then will help the cleaning.
In response to the car being allergic to high octane 
that must be crappy gasoline then the premium fuel additives/better performance due to higher octane starts cleaning thing;. build up comes off
The only serious accounts I have is a b8 s5 that is the v8, on a french e85 forum. Hes given multiple accounts of it all he has done is the adapter from the ECU controlling the pump/injectors. Over 100,000 miles no issues except early on the clogged injectors (replaced under warranty/goodwill). The wear as you’ll get maybe 10 % more power that will mean more wear. Need to halve the oil change intervals as there is some metal in engine oil incompatible with ethanol. I believe the tests in a paper I read regarding the gunk on the injectors were carried out in western europe where the fuel is mostly the same ie has the same additives. Depends a bit on which season.