I know most of you know this but this is for the guys not familiar with detonating. In a nutshell, the higher the octane rating the more compression or heat from compression the fuel can take before detonation. If you run low octane fuels in high compression engines the fuel will detonate from heat caused by compression prior to the piston completing its upwards "compression" stroke. Causing the the engine to "knock". Once the detonation happens, the piston still has to complete its upward stroke and any momentum it had traveling up will be slowed because its basically running into an explosion and then trying to run through it. Which can also cause engine damage. When octane is too high for a certain compression, the heat from combustion is not enough to have a complete burn when combustion occurs, so not all of your fuel is getting burned off. If everything is in order, the heat from compression alone puts the fuel just below the flash point, then the spark from your spark plug puts it over the top and ignites the mixture. The piston would be at the very peak of its stroke and would then be pushed down due to the energy released during combustion. Either way, whether or not you have too low of an octane or too high of an octane you will loose the ability to achieve the desired RPM in which the machine was designed to run at.