Though many motorcycle owners don’t realise it, their bikes may be equipped with electronics that detect engine knock. When the motorbike’s inbuilt computer adjusts ignition timing to eliminate engine knock, essentially altering the motorcycle engine tuning, the engine performance suffers.
What is engine knock?
Understanding engine knock, also known as “detonation” or “pre-ignition”, requires an understanding of fuel octane. Fuel octane is a standard measure of petrol performance. The three most common fuel octane ratings include:
• anti-knock index (AKI)
• research octane number (RON)
• motor octane number (MON)
AKI is a rating that most motorists are familiar with. It is typically displayed on petrol pumps as the average of the fuel’s RON and MON. RON, however, is the most common industry rating. AMSOIL therefore uses RON when conducting engine performance tests and product validation. A petrol’s RON is generally a few numbers higher than the AKI posted on the petrol pump (e.g. 87 octane fuel, or regular pump petrol, has a RON of about 91-92).
The higher the fuel octane, the more compression the fuel can withstand before igniting. Low-octane petrol is susceptible to uncontrolled and early ignition in the motorbike’s combustion chamber. It causes engine knocking or pinging, causes engine performance to deteriorate and, left unchecked, can cause severe piston damage.
Engine tuning and detuning affect the motorbike engine’s performance
Some modern motorbikes are equipped with an engine knock sensor that adjusts timing to compensate for low-octane petrol and eliminate engine knock – but it detunes the engine in that same process. Unfortunately, engine tuning plays an important part in the engine’s performance. Rough idling and lack of throttle response are the most common side effects of the engine detuning to save itself from low-octane petrol. As most motorbike engines do this automatically, many people don’t even know this is occurring. Engine knock may be eliminated by raising the fuel’s octane number.