Yeah shouldn't be an issue. 93 here has 10% E anyways so my tunes probably fine to run it almost dry and switch the map and fuel. Come winter the E drops to E70 so you're even closer.

Exactly, its not that sensitive. Just for the sake of seeing the actual difference, lets look at some math:


Say you make the switch with 3/4 a gallon of E10 gasoline left in the tank...

In the tank you have:
0.075 gallon ethanol
0.675 gallon gas

You add 18 gallons (it should take more like 18.5) of E78 (just a random typical "e85" pump content):

You just added:
14.04 gallons ethanol
3.96 gallons gas

You now have in the tank:
14.115 gallons ethanol
4.635 gallons gas

With a total 18.75 gallons in the tank:
14.115 Ethanol / 18.75 total = .7528%

You have E75 in the car. This will not be a critical difference from E78.

Exactly!!! And if u really want to u can make a custom map for 50/50 so if u have to fill up with 93 at before a long drive u dont have to waste the half tank in there by driving around till E

Don't mind me, I'm just paranoid.

Or you can go to your local track with a gas container and get E98 for $4/gal and then add in the difference to bring you into the safe range. Ive done this for a road trip once.