I have seen that gm has produced vehicles that run on it for awhile, but the gas station i go to just started selling it and it is 40 cents cheaper than 87, i was on empty so i put 2 gallons in my blazer and it ran like crap, is this bad and what would you need to do to an older car to have it run good on this stuff.  

E85 has a lot less energy in it so you have to burn a lot more of it to do same work. A gallon of it will not take you as far as a gallon of gas. You are not saving any money with it at 40 cents less either. To use E85 you need to for one have a fuel system that can flow/feed a lot more fuel into engine when running E85. Doing this with a carb would require it to be re-jetted properly and after re-jetting it would no longer be able to run on gas because it would be over rich big time. Flex fuel cars have higher capacity injectors that can flow more fuel, corrosion resistant fuel lines and different ECM programing to be able to adapt to E85. The nice thing about E85 is that if you were to build a engine to run only on it and not gas you could use very high compression (12 or 13 to 1) because E85 has a very high octane (around 105) and this would make a lot more power and increase MPG on E85 too, Price aside, as long as you make a engine tolerate 87 octane fuel too as well as E85 you will never come close to harnessing the full abilities of E85 as a motor fuel. Properly built it could shame on pump gas engine on power.