Let's put it this way. A gas motors' stoich AFR is 14.7:1, whereas E85 should be 9.7:1.
The real benefit of running it is with boosted or high compression applications though. I plan on running my 2.3 turbo at 10.5:1 compression ratio with a lot of boost, whereas on gas I'd have to keep it closer to around 8-9:1 CR (stock CR is 8:1). The E85 is much less likely to detonate and blow a huge hole in the side of your motor.
This guy Schoneck Composites was a leader in E85 in our area for a long time. He had many customers cars in the King of the Street competition in Muscle Mustangs and Fast Fords. It's everywhere in this State, so many racers use it too for the octane benefits. My buddy has a 74 Dart with a Nascar truck series motor in it putting down 750 hp on E85. Just have to remember also that's it's not always a consistant mix. Kind of like summer and winter blend diesel. They change the ratio of Ethanol/gas during the winter months.
We've been running E85 in my stepson's 87 Notch bracket racer for the past few summers. Although its carbed, we had to get a bigger fuel pump & lines & send the carb to Pro Systems for the E85 convsion & tune. The car runs awsome, way cooler, way less cost than race fuel. I bought a E85 tester that I test pump E85 before buying.
I have converted quite a few stangs over, from foxes to 07's. There is a lot of misinformation and myths out there about E85.
No, you dont have to change lines or tank.
Yes, you will need a higher capacity fuel pump.
Yes, one step larger injectors is a good idea.
Average increase in demand is around 19% n/a.
Remember, nearly all of our cars currently run on E10. That means your fuel system is already handled ethanol in it.
Yes, there are two different grades of E85, E70 and E85, and all kinds of blends in between as tanks with some E85 in them get E70 dumped in the fall and vice versa in the spring. I highly recommend a tester be carried in the car. You,ll need two tunes, E85 and E70. A switch chip can handle it.
Another note, unless your car can benefit from a lot higher octane, there is no performance gain, and a substantial loss in mpg. Most of my street cars run on 87 and make their best power, unless compression has been increased.