User: What number octane gas should be used for combustion engines in vehicles?
Assistant: Manufacturers list the minimal octane to be used on specific vehicles in the owners manual. Always check the manual to be sure the proper fuel is being used. An octane number such as 87, 91, 93 indicates the amount of heat tolerance of the fuel before igniting inside the engine cylinder. The higher the octane number, the higher heat tolerance. If you use the wrong octane in a vehicle, such as using 87, rather than 93 for a high performing turbo or supercharged vehicle, the engine could produce knock or pre-detonation. Knock occurs when the timing of of the air and fuel mixture in the cylinder explodes too early and can cause serious damage to the engine components. Knock is also something you can hear and feel and can be noticed by the driver. Having the detonation of the air and fuel, produced by the spark plug that is intended from the factory is optimal for the longevity of the vehicle.