The Octane Question

Nov 11, 2019 | Articles, The Octane Question

Octane Rating.

Are you familiar with the meanings of octane ratings? Many people concede that they know only that their cars run on petrol or diesel. Many also know – either from word of mouth or manuals – that a certain octane is the most befitting to use. Unfortunately, not many fully understand what the ratings mean. What petrol should you put in your car? Does the higher octane rating give your car more power? Can fuel with the wrong octane rating damage your engine?


In short, the higher the petrol’s octane rating, the higher the compression it can withstand before spontaneously igniting (detonating). In petrol engines, the air/fuel mixture is ignited at precisely the right moment. The car’s electronic control unit (ECU) determines this ignition. What happens when you use a fuel with a too-low octane rating in an engine with a high compression ratio? Well, the fuel may pre-ignite due to a myriad of factors. A moment later, the mixture is ignited again. This time in the normal manner. This will create a shockwave due to the collision of these two explosions. Many know this as a “knock”. Characteristic of a knock is a noise that sounds like clattering or rattling.

A modern ECU-controlled engine can usually detect knock and will compensate for it by adjusting the timing to eliminate it. This may, however, cause a reduction in power and negatively affect fuel consumption. Older engines that cannot compensate may experience irreparable damage. High-compression engines are more powerful and more efficient than low-compression engines. These engines also run hotter and experience higher combustion pressures. That is why they require high-octane petrol. For this reason, some engines cannot run on 91- or 93-octane petrol at all and requires at least 95-octane.

High octane

It stands to reason that high-octane petrol cannot damage your engine, even if your engine does not require it. High-octane petrol will be just as effectively ignite than low-octane petrol. It, therefore, does no harm to put fuel with a too-high octane rating in your tank. This is also what you should do if you are in any doubt. On the contrary, too-low octane petrol can cause some engines to run poorly or even damage them. When in doubt, use the highest octane. The octane rating your engine requires will usually be shown inside the fuel flap, or in the instruction manual.

Lastly, higher octane does not mean more power. Why do people think that high octane means high power? Because modern, powerful, high-compression engines usually require a high octane to run properly. Also because a lower octane may cause them to compensate by lowering power output in the interest of self-preservation. If your vehicle is designed to run on low octane, a higher octane rating will yield no extra power.

If you want extra power, and better fuel economy, then there is a simple way of getting it. Simply fit a Unichip and you will be sure of the best performance and efficiency your engine can offer. Do not miss out. Click here to contact us and have our technicians fit your Unichip today. If you want to read more about the octane rating conspiracy, click here. If you want to hear what they answer on the question: “Should I use 93 or 95 octanes?” click here. Safe driving.



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