We get a lot of questions about fuel metering changes required for oxygenated fuels... and that is a good thing, because racers should be asking those questions.
Luckily, the answer is not necessarily complicated.
Let’s look at Sunoco EXO2 for instance. It’s a good fuel to use as an example because it contains 10% (by weight) oxygen. Without proper fuel enrichment, you won’t find the power you’re hoping for, and in fact the engine may not even run well.
Alcohols like methyl alcohol (methanol) and ethyl alcohol (ethanol) are often used in race fuels. Sometimes they are a small part of the fuel and sometimes they are a primary component of the fuel. Methanol is commonly used “straight” – that’s why it’s called racing alcohol by many. Ethanol can also be used straight, and some racers do, but it’s more common to hear about E85, a blend of about 85% ethanol.
Much has been said about the octane rating of alcohols. However, technically speaking, the octane ratings of alcohols can not be measured.
All octane test engines, as defined in the octane rating procedures set forth by the American Society for Testing and Materials (ASTM), are carbureted. Air/fuel ratio adjustments on octane engine carburetors are limited and can not accommodate the extremely different air/fuel ratio requirements of pure alcohols.