This post is extremely old going back to the beginning and lots has changed, lots in here is false or incorrect as well.
E85 increases performance which in turn has decreased fuel mileage. I have a flex fuel truck, 07 avalanche and when I run e85 my mileage reduces by an average of 4 to 5 miles per gallon, and if I tug anything out back, it falls far worse in overall averages.
The amazing thing is the difference in performance across the board. Off the line acceleration is far better, and there's benefit on the top end as well.
The problem is for a heavy right footed driver, you'll spend more on the e85 fuel than on the low grade guaranteed. For a driver that can stay out of the pedal, you'll likely brake even in the same comparison or save a little over the year, but cost in prepping the fuel system will sway you back to the red.
A lot of negative publicity came out with e85 and much of it was not true.. I'm no green tree advocate, don't really care about emissions and ozone. I'm not that type of person, but E85 is extremely clean both in processing and it's burnage in actual use.
Bottom line it's corrosive, you cannot just dump e85 in the tank and go. You have to be tuned for it obviously as well otherwise the benefit is nil. Don't forget them cats will likely cease as well over time, it's not like running c16 but it does act in that way over time. Todays oem e85 cars adjust for the fuel grade on the fly via chat to the computer off the 02 sensors so you do nothing when using any of the available grades. You could essentially on our mustangs run a seperate tune on e85 fills and it would be the same thing. Just have to be conscious of changing the tune.
Here's the kicker, our fuel rails are not welded, they are soldered, turn one over and take a peak. These will over time corrode. You will have to replace. Parts of our pump wiring and hosing are nut up to spec either. Keep in mind most of the system would / could hold up for a duration of time and then fail. Injector o-rings included. It won't be an overnight failure, it's not that corrosive. Plugs are an issue from the increased burn on ignition, you essentially would over heat stockers and net pre-ignition.
Here's an article on a terminator converted to e85 in 5.0 magazine a while back.
http://www.mustang50magazine.com/techarticles/m5lp_0709_e85_terminator/index.html