TL
R - Search online for "ethanol fuel calculators", yes, they do let you put in 10% for the base fuel too and you can see what percentages come out to be but don't worry about it, just use a couple of gallons total of e85 with whatever 91 or 93 you find and you should be fine... I.E. if refueling with 1/4 tank left of the E mix already in there, just use 1.5 gallons of e85 with the rest premium on your refill.
Further info/discussion... I've ran e30 on 3 different cars in a row now and car say that in general turbo cars LOVE ethanol for the intake charge cooling effect. If your car ran terrible with 10% 93 octane, it wasn't the ethanol part, the gasoline part was a poor/winter batch. But yes, ethanol free absolutely gives better mileage but turbo cars prefer ethanol, I'd say 20%/E20 would be ideal even for a standard non-ethanol tune. I've been trying to run aggressive JB4 Map 6 tunes with IS20 on my 1.8 and was getting corrections that I wasn't with the same fuel on IS12 but just 2 gallons of e85 in my tank for e20 total led me to zero corrections and 2 more PSI on my custom JB4 map.
PS, thanks to those who mentioned how aggressive the timing is with Unitronic to help me rule them out for my flash tune. One of the biggest issues for me is even the 1.8 stock tune uses too much timing advance, which hinders JB4 performance as well. So I'm gonna go with APR, which cuts the amount of timing advance and pushes even higher boost instead, so it will be very stackable with my JB4. Honestly, even if the turbo fries, IS20's are like $200 for low mileage ones and even if you are too lazy to install yourself there are shops/mechanics that won't rip you off and only charge you ~$500 labor to have done for you. So $600-800 parts and labor for a turbo replacement is worth the right stackable tune to me, hehe.
Edit: I was wrong, it was the opposite, Unitronic is actually ideal to stack because you can't adjust timing with a JB4 but you can certainly add boost. APR tunes already have tons of boost so it's ideal for poorer fuel and non-stacking as a one and done tune.
