People think higher octane equals better quality fuel. Wrong. Octane rating prevents pre-detonation, not performance gains. Lower octane than your engine requires causes knock. The fuel air mixture combusts prematurely before the engine wants it, causing long term wear and damage. But using higher octane than required provides zero benefit unless your engine has adaptive timing that adjusts based on fuel quality. Most cars don’t. Using 91 in an 87 octane car wastes money. Using 87 in a 91 octane