HOW DO THEY GET OCTANE NUMBERS ABOVE 100?
Often it’s done by pure extrapolation. A more reliable method, however, is through the use of so-called performance numbers. Briefly, these are arrived at by determining the instantaneous mean effective cylinder pressure (IMEP), using the fuel under test, at the highest boost that does not cause knocking. This number is then multiplied by 100 and the resultant is divided by the IMEP at the highest boost that does not cause knocking on the 100 octane equivalent fuel. Note that, technically, there is no such thing as an octane number above 100. If you’re at a party, avoid saying things like “110 octane gasoline” because people will get up and walk away from you. You should say, instead, “a gasoline with a performance number of 110.” That will bring the help scurrying over with more champagne.
