Originally Posted by
Ron Blum
Please make sure that the octane ratings that you are discussing are measured the same way. The last post mentioned AKI (anti-knock index). Remember that automobile fuel is based on (R+M)/2 and aviation fuel is different. On average aviation fuel is labeled ~5 points above automobile fuel. In other words, 100LL is about equivalent to 94/95 octane (AKI) automotive fuel. Are the numbers in your first post for aviation or automotive fuel octane? Just trying to be careful.
In addition, remember that autofuel may or may not have alcohol (some states require that to be labeled on the automotive pumps). Also, there are summer and winter blends of autofuel. The RVP (Reid Vapor Pressure) is changed (made more volatile) to make cars easier to start in the winter. This can be an issue with vapor lock if used in hotter or heat soaked conditions on airplanes (and more prevalent on low wing airplanes).