In addition to some of the other obstacles/problems that some have already mentioned you would also have to give the carburation some attention. On the plus side I believe alcohols typically burn cooler than gasoline so your engine would run cooler as well.
Originally Posted by Comrade Alfonzo
It wouold eat the seals, E85 is more corrosive and it is approx 105 octane so you would be going faster when everything locked up
It's a common misconception that a high octane fuel will give you more power or make your engine 'go faster'. The octane rating refers simply to the fuel's resistance to pre detonation, a problem with high(er) compression engines. You compress a fuel mixture enough and it wants to ignite without a spark (the principle behind diesel engines). The more you compress the same mixture the more energy (power) it will give when it's finally ignited. All things being equal, if you have say a 8.0:1 compression spark ignition engine whether you use 89, 92 or even a 105 octane fuel it won't make much of a performance difference. If your engine has a 10:1 or higher compression/performance engine you need the higher octane gas and you will get more performance but it's mainly because of the design of the actual engine rather than the octane rating.
Engines that run alcohol for fuel (like dragsters) have quite a few different modifications as compared to gasoline engines. Also, maybe someone will correct me on this but E85 isn't pure ethanol, it's a gas/alcohol mixture of some sort?