Originally Posted by 328i M-Sport
Higher octane is more resistant to detonation. It can make more power by not reducing timing to avoid knocking.
If the car does not have a high compression engine or advanced timing, it will not benefit from it. Higher octane gas in theory actually burns slower. And most brand name gas stations put the same cleaners into the fuel for any octane.
IF engine was designed to do so. This TV show proved that a car designed to run on 87 got worse gas mileage and polluted more on 91 as it was unable to process the fuel correctly.