We published an article about what octane means some time back. But then there is the question of whether you can use petrol with a higher octane rating than what your motorcycle's manufacturer recommends?

Most gasoline (petrol) powered vehicles sold in Malaysia are recommended to use RON 95 petrol as the minimum octane, while some high performance cars and some motorcycles are required to use RON 99 or higher. So, can I use RON 97 or RON 100?

A bit of recap

To recap, DO NOT mistake higher RON rating as "the fuel containing more power." Neither should we think higher RON fuels have "better cleaning" capabilities.

Instead, fuel RON (Research Octane Number) is simply the fuel's ability to withstand pre-ignition.

Pre-ignition is a condition of the fuel and air mixture self-igniting during compression, before the spark plug sets the mixture alight at the proper timing. The fuel and air mixture increases in temperature as it is squeezed tighter and tighter in the combustion chamber as the piston rises during the compression stroke. Pre-ignition sends out flames along with a shockwave at the speed of sound all across the combustion chamber. A loud knocking or pinging sound can be heard when this occurs. Pre-ignition is bad and will destroy the engine!

An engine with a higher compression ratio will squeeze the mixture into an even smaller space compared to an engine with a lower compression ratio. In other words, the fuel and air mixture will get much hotter. As such, a high compression engine requires higher octane fuel to stave off pre-ignition.

Higher performance engines generally have much higher compression ratios, such as 14:1 and above. Conversely, "normal" road bikes have compression ratios ranging from 10:1 to 13.5:1. Consequently, we only need to use the minimum recommended fuel octane.

To give you an idea, MotoGP bikes use fuels between RON 95 to RON 102.

Okay, okay, so can I use higher octane fuel?

Yes, of course. Using higher octane fuel is okay. However, bear this in mind: The higher octane fuel may not offer much benefits over the lower octane fuel, not to mention having to pay more especially with super expensive RON 97 these days!

And in some cases, you may find your exhaust tip turning black rather than a rusty brown when you do so. Why? Because some of that fuel is unburned as higher octane fuel resists burning too quickly, and the remainder is ejected as soot. The only way to fully utilise higher octane fuel is by retuning your engine's ECU to cater for it.

However, NEVER use fuel with an octane lower than the minimum recommended rating. For example: Your bike needs RON 95 but you use RON 92. That will have your engine knocking itself to smithereens!