Fuel can be ignited by spark or compression. In simple terms, the octane rating says how well the gas can be compressed without igniting. If the gas ignites by compression you get "knocks" - bad. Thus if you have no knocks, you probably have the "right" level of octane.raymondo said:How bout a little insight into what octane actually does.
Higher compression engines need higher octane fuel thus the different octane offerings. Putting in a higher octane fuel than is needed by your car to avoid knocking (compression ignition) is a waste since you are either knocking or not. Octane itself does not dictate the explosive force - the compression of the engine does.
Technically, cracked crude oil produces: methane, propane, butane, pentane, hexane, heptane and octane. Octane is the best at handling compression. An octane rating of 91 means that 91% of the fuel is "equivalent" to octane (close enough for this discussion). "Equivalent" since things like lead can be used as cheap octane fillers.