E85 has 75% of the BTU per gallon of regular ol' 87 octane fuel (with 10% ethanol), so the break-even is when E85 costs 3/4th what regular fuel costs.

So, if 87 octane is $3.20 a gal, then if E85 is less than .75x3.20 or $2.40, then it is a better deal to burn E85. My truck loves E85, you get a little more HP and better charge cooling and higher anti-knock index, so the spark knock sensor will permit earlier timing.

Good?