E85, often called Flex-Fuel and made for Flex-Fuel Vehicles (FFV) is a mixture of up to 85% denatured (you can't get drunk off of it) ethanol fuel and gasoline. E85 is widely used in Sweden and elsewhere in the Europe and is just now picking up popularity in the US despite the existence of Flex-Fuel vehicles having been made available by Ford and GMC for some time now.

One of the primary benefits of E85 is that it has a much higher octane rating than gasoline. 100-105 vs 87-93. This means that you can run higher compression engines and gain more power from the system.

Unfortunately most Flex-Fuel vehicles can run E85 or regular gasoline (hence the term 'flex') and so they run regular compression ratios (9:1) as a higher compression ratio that would gain more power from E85 (around 11:1) would have catastrophic detonation if it were to run regular gasoline.

Depending on your vehicle, you can convert it to run E85, though many vehicles need various aluminum and rubber components replaced to do so.

Because of the compression ratio issue, E85 does not yeild its full potential in most vehicles. This causes E85 to typically yeild lower MPG than regular gasoline. However, in the mid-west E85 is often as low as 40% less than gasoline at the pump and works out to costing around 90% of gasoline.

If you are a proponent of lower emissions and environmental responsible, then E85 is a good choice as well as the fuel is primarily made from corn and it produces much cleaner exhaust than gasoline.

One useful application for E85 is as a fuel in vehicles from the 60s as compression ratios over 11:1 were not uncommon and currently owners of such cars have to add octane boost to their gasoline to keep their engines from experiencing detonation. There are caveats as most carburators are made of aluminum, which doesn't get along with E85 well, but there are ways around that.

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