Originally Posted by Sibze

He wasn't really joking. Don't use anything under 91... the engine is not made for it.

The hole idea behind the octane level is:

The higher the octane level the more pressure that it can withstand before the fuel self-ignites. If enough pressure builds your engine will basically start burning before the piston reaches optimum position, causing the engine to "jerk" internally… It wont sounds very good.

Also it burns at a slower rate, so in a vehicle that requires 87 octane there is the potential that running higher octane fuel (or high enough, say 110 octane race fuel) will result in unburned fuel leaving the combustion chamber (ie, less power) and going into your catalytic converters, eventually clogging them (a lot less power)