93 and 95 Octane fuel

At the time of writing another petrol price increase hit consumers on Wednesday 1 June at 52c a litre. With the weakening rand and price increase in petroleum, the price of fuel in South Africa continues to climb. Sowhen we drive up to the pumps to refuel we might ask ourselves what the difference is between 93 and 95, and how each type affects our vehicle's engines.

Higher-octane fuel can withstand higher levels of compression and therefore is able to perform at a higher level. So does that mean that if you want your car to go faster you should fill up with 95 octane instead of 93? How do you make the choice and does it really matter?

What is Octane Rating?

Octane was used in fuel to stop pre-detonation in engines or fuel from igniting. The pistons in a car's engine compresses a cylinder of air and gas before igniting it by means of a spark plug (http://auto.howstuffworks.com/ignition-system.html)and thus creates the power that the vehicle requires to move.

The octane rating indicates the amount of fuel that can be compressed before it spontaneously ignites. Higher octane fuel is more stable and produces better efficiency and power, while lower octane fuel will handle less compression before igniting.

What Octane Should I Use?

Your car's engine compression ratio determines what octane fuel you should fill your car up with. Engines with high compression ratios have more horsepower and require a higher octane fuel. The more stable higher octane fuel reduces the risk of igniting, allowing better performance and efficiency.

The simple answer is that high performance cars require the higher 95 octane, while your average road vehicle will run suitably well on 93 octane. It's highly unlikely that an average car will see any performance gain by using 95 octane. The AA recommends that unless your engine is turbo or turbo-charged, you should choose 93.

Having said that, there may be exceptions that are influenced by various factors such as altitude,and driving and environmental conditions. If in doubt, consult your vehicle owner's manual to ensure you're filling up with the optimal type of fuel for your particular car. Who knows, you might find yourself saving a few needed rands.


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