Why Octane Ratings?
What purpose do octane ratings serve? In short, they measure the fuel’s resistance to detonation, or the premature ignition of the fuel/air mixture during the engine’s compression cycle. Marketing on the part of the oil companies and auto manufacturers has perpetuated the notion of octane ratings, which are classified by the Research Octane Number (RON) or the Motor Octane Number (MON). Both measure the fuel’s resistance to detonation, but the MON measures the engine under load (i.e. towing) and so is roughly 10 points lower than the RON. RON is the measure found across Europe, while North America uses an average of RON and MON. This detonation is also known as “knocking” — an annoying and, in the short term, largely harmless condition of reduced efficiency and power. The operative word here is “was,” because with the adoption of modern fuel injection; engine knock sensors (generally after 1984); and unleaded fuels (1988), these timing/fuel related issues have essentially been allevia
