i dont get it then. ive been hearing stuff about how 91 premium can hurt the car. i've always thought the higher octane the better because you have less chances of early detenation. yes, running higher octane fuel might not do anything for the car performance or mileage wise, but you have a lower risk of early detenation. you go to any manufacturers website and they always have the recommended fuel for the car OR higher. recommended gasoline for the tC is 87 octane OR higher. same goes for cars that are 91 premium recommended. so how will higher octane fuel be bad for the engine when the manufacturer says its ok?