Remember; octane is a measure of a fuel's ability to prevent detonation, nothing more, higher octane is not hotter, it is not more powerful, it will just prevent detonation, which is caused by excessive heat and/or pressure. Heat and/or pressure, as they increase, make more horsepower, up to the point where the fuel starts detonating. When a fuel starts detonating, long before you can hear it, the horsepower starts dropping. Preignition, a situation where the fuel spontaneously ignites, before the spark plug fires, is not detonation. Preignition is often caused by too hotter of a spark plug or a deposit in the combustion chamber which is hot enough to ignite the fuel mixture.