I have been wanting to play with E85 for a couple of years now. Cental Florida has been slow to get it, it has not been available until just recently. I found out on Friday it can be purchased from the Turkey Lake Service plaza on the turnpike (3.49 gal on 7/4/08). Until now, it was only available in Tallahassee, recently Miami, and at a biofuels distributor in Lake City. On my way back from Texas last month I picked up a barrel from the bio fuels distributor in Lake City (N. Florida) for testing, these guys mix their own E85 so it is very consistent fuel. Most E85 pumps claim up to 70% ethanol, so you *should* be getting E85 in the summer and E70 in the winter, which is enough of a difference to require a tune change.
E85 is cheaper by the gallon, but due to the 20-40% fuel economy loss, it's not usually any cheaper overall. There are some things I can do to help with the fuel economy loss by applying my fuel economy tuning, but it only offsets the loss by 5-10% at most. The fuel economy loss is due to the much lower energy content of ethanol, it also means you need much more fuel by volume. E85 really taxes the fuel system, the stoich point of normal gasoline is 14.64, E85 is about 9.85, 14.64/9.85=1.48, so you need roughly 50% more fuel mass to run E85.
A discussion on fuel demands and supplies...
The stock 05+ Mustang GT and V6 Fuel pump is capable of delivering about 4lb/min of fuel. The stock 05+ pump is the "Focus pump" that we install in the older 99-04 cars as an upgrade, it flows similar to the Ford GT pump and Aviator pumps.
A stock Mustang 05+ GT uses about 2.5lb/min of fuel peak, while a V6 uses about 1.7lb/min peak. The older 99-04 cars use just a little bit less than that.
2.5 lb/min fuel requirement on gasoline X 50% increased fuel demand for E85 = 3.75lb/min, which is how much fuel an 05+ GT should need to run E85, and my testing on Mike's car found that to be completely correct, which is still within the capacity of our stock pump.
The stock 05+ GT 24lb injectors aren't as well off as the stock pump, at the standard 40psi of fuel pressure they can only supply enough E85 up to about 5000RPM. If we do the math, they can only supply about 3.2 lb/min of fuel at 40psi. The workaround is to raise fuel pressure up to 50-60psi to get more flow out of them. The factory tune actually has all the parameters already set up to do this, so you don't actually need to change anything to get more out of them to run E85. Raising fuel pressure makes the pump work harder, but duty cycle still sits around 90-95% on E85.
The real value to us in E85 is the high octane rating, about 105. It is a very cheap race gas for boosted cars, assuming your fuel system is up to it. And based on our testing below, it seems to add power even in NA applications (more on that later).
Recently we put one of my local customers cars on the dyno to test E85 in it. He has an 08 Mustang GT Manual with a C&L Racer intake, CMCV deletes, stock cats, and magnapack mufflers. I made some baseline pulls on his 93 tune with around 12.7 A/F (.87 lambda), this car is able to run 30-31* of timing at WOT with no major knock sensor activity.
We then drained the tank and put in 8 gallons of E85.
I got the tune set up for E85 and dialed it in to run the same lambda that I was running on 93. I've found that a lambda of .86 to .89 (12.6 to 13.0 in gasoline terms) works best on these 3V motor. Going to .92 lambda on E85 (about 13.5 in gasoline terms) caused a power loss.
On E85 the car did not run significantly more timing, there may have been slightly less knock sensor retard, by 1/2 degree or so.
Now onto the results, the car gained 9RWHP and 9RWTQ on E85. This is totally suprises me, but is consistent with another 05+ GT owners results found
here. The additional power could be from the oxygen locked up in the fuel, which is realeased during combustion or from the cooling effect of the greater fuel volume and the alcohol. On boosted cars, the gains will be even greater because of the additional timing that can be run on E85, due to the additional octane.
http://vmptuning.com/dynographs/mikeE85vs93.jpg
The alcohol in E85 is corrosive. The fuel systems in modern vehicles is designed to deal with a small amount of alcohol, 10%, which is now being found at many pumps in the form of E10 gasoline.
For short term use, E85 should not cause problems with fuel systems in newer non-FFV vehicles.
Mike left with half a tank so we can see how much gas mileage changes without doing any special fuel economy tuning.
I also plan to test E85 in a V6 and a GT500. I don't know if all naturally aspirated vehicles will gain power on E85 with no timing change, like the 4.6L 3Vs, further testing will be required.
E85 testing on NA 08 Mustang GT 4.6L 3V 
