Usually, fuel octane is important to an engine because of detonation. There are alot of factors that will cause an engine to 'ping', but it is usually due to the combustion chambers heat, or advanced timing. Retarding the timing(if possible on the new cars), will lower the temperature in the engine. Detonation is actually an explosion, rather than an even burn of the air/fuel charge within the combustion chamber. It is literally like taking a hammer to the top of the piston. 94 octane fuel will actually cool these temps. It also becomes easier for the engine to maintain an even burn. When leaded fuel was phased out, the fuel companies had to used something else to cool those temps. What they mainly added was sulfur.