Alcohol and Octane
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.