Gotta mix 3 gallons e85 to 12 gallons of 93 for the proper mixture, choose the map and enjoy. Ive been running it for a while, very addicting power increase.
This isn't correct. First, the tank doesn't hold 15 gallons, it holds 12.4. Also, about 2 gallons of that is reserve, so you'll only ever fill around 10 gallons or just over, which doesn't change the calculations, but makes fill ups easier which I'll explain later.
Now this is where everyone seems to overcomplicate things. When you want to switch from 93 to E30, you don't need to run it empty, you just need enough room to fill enough E85 to hit E30, then top off with 93, and that number is about 4 gallons for the first fill up.
Some math to validate, assuming you're getting full 85% ethanol E85 and about 5% ethanol 93:
4 gallons x 0.85 = 3.4 gallons of ethanol
8 gallons (of 93 for a full tank) x 0.05 = 0.4 gallons of ethanol
Total ethanol: 3.8 gallons
3.8 gallons ethanol / 12.4 gallons total = 0.3065 or just about dead on E30.
After that, just fill 2:1 93 to E85:
1 gallon E85 * 0.85 = ... 0.85g E (0.15g unleaded)
2 gallons * .05 (E in 93) = 0.1g E (1.9g unleaded)
For a total of 0.95g E, 2.05g unleaded
And finally, .95g (E) / 3g (total) = 0.3167 or E32 rounded (Fill up just a little bit more 93 than E85 if you are concerned about that 2% increasing over time)
No need for any kind of calculator app. The fact that 2 gallons are reserve and the gauge measures roughly 10 gallons makes things REALLY simple. I typically just fill up at a quarter of a tank, so you can fit 7.5 gallons, so add 2.5 gallons E85, then 5 gallons 93. You aren't going to fill it to the brim every time, but you'll be close enough without having to do calculations at the pump. One thing to note, ethanol mixes well with gasoline, but if you do an initial fill with my method above, I get back in, start it up, then change my map, then stay out of boost for a little bit while I let it mix up. It should do so pretty quickly as you drive.
And the only time you need to drive to empty is switching from E30 to 93. Even then, you don't need to drive to fumes, just to close to E. The car can handle up to, I believe it was E15 with normal fueling.
And yeah, I daily drive E30 in mine because I'm lucky enough to have two E85 stations within a mile in either direction of my house and work. I tested them out to be about 83% ethanol, so that makes my 2:1 mix pretty dead on that E30 mark.
Hopefully that makes things a little easier!