Q: Which fuel should I use, 91 or 95?

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I would like to know which fuel grade (premium 91 or premium 95, both are available in KSA) I should use in my car.

My car has 400000 miles.
My car has a manual transmission.

Hi There, Octane rating is the measure of a fuel’s ability to resist "knocking" or "pinging" during combustion, caused by the air/fuel mixture detonating prematurely in the engine. Most gasoline vehicles with factory engines (assuming no modifications) are designed to run on 87 octane, but others are designed to use higher octane fuel. Higher octane fuels are often required or recommended for engines that use a higher compression ratio and/or use supercharging or turbocharging to force more air into the engine. Increasing pressure in the cylinder allows an engine to extract more mechanical energy from a given air/fuel mixture but requires higher octane fuel to keep the mixture from pre-detonating. In these engines, high octane fuel will improve performance and fuel economy. Using a lower octane fuel than required can cause the engine to run poorly and can damage the engine and emissions control system over time. It may also void your warranty. In older vehicles, the engine can make an audible "knocking" or "pinging" sound. Many newer vehicles can adjust the spark timing to reduce knock, but engine power and fuel economy will still suffer. As always, it is best to refer to your vehicle’s specific owner’s manual which will indicate the specific octane requirement for your vehicle’s engine model.

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