the big problem is getting the EPA to pass it, that's mucho $$$
from Wikipedia
http://en.wikipedia.org/wiki/E85#After-market_conversionsAfter-market conversion kits, for converting standard engines to operate on E85, are generally not legal in U.S. states subject to emissions controls, unless you get your converted vehicle independently EPA certified. This is despite the fact that the exhaust emissions from any such converted cars are improved by utilizing higher percentages of ethanol in the gasoline blend. Unfortunately, EPA certification costs in excess of $23,000 and you additionally have to prove that your vehicle will maintain low emissions for at least 50,000 miles after the conversion. Most individuals won't give up their vehicles for the requisite 50,000 mile test period. Ethanol can be made out of pretty much anything grown on a farm and of what livestock eat. Likewise, conversion kit manufacturers generally don't certify their kits due to the onerous and expensive burden of these laws. The kits would have to be tested with every model vehicle for which they are to be sold. If a kit is already certified as described, the EPA Federal Test Procedure for an individual's conversion costs $750.00. One can request a reduction of payment of down to 1% of the car's added retail value due to the conversion. A minimum fee may apply if the value added is not seen to be very high.
Similarly, U.S. Federal law prohibits the manufacture of many such conversion kits for sale in the U.S. unless they are EPA certified. The origin of this ban dates to when conversion kits for using compressed natural gas were originally sold. The ban was enacted to prevent the sale of such conversion kits due to safety concerns. This ban on the manufacture of kits is at odds with the fact that these kits, once existing, are legal in all states but CA, and most states offer some sort of tax break for converting your vehicle (See tax breaks.) One Brazilian after-market kit is available legally in US States that do not have restrictive emission controls.