Understand When & How To Use Higher-Octance Petrol For Your Car To Save Cost

According to the oil companies’ claims, some cars can produce more power by using high-octane fuels. And while engines designed for lower-octane petrol won’t provide more power using high-octane petrol, they may be less likely to develop knocking.

The higher octane may benefit your car in one of the following situations:

• You have a high-performance (especially turbo-charged) car designed for high octane fuel.
  
• Your car has a sophisticated knock sensor (currently found on some high-performance and luxury models) that actively tunes your engine (for example, spark plug timing) to the maximum possible setting before it starts to sense knock. It can therefore take advantage of the higher octane rating, and actually increase the power output of your car.
  
• You’ve noticed a decrease in your car’s power. This may have been caused by a passive knock sensor found on most modern car models. This type of sensor doesn’t kick in unless it actually detects knocking. It then tunes down the car’s engine, reducing the tendency to knock — but also the power output. Using a fuel with a higher octane rating can prevent that, so the engine can work on its normal power output: if you’re using regular unleaded, you may want to try premium unleaded instead. If you’re already using premium unleaded, one of the high-octane products may improve things.
  
• Your car’s engine knocks when using regular unleaded, premium unleaded or lead replacement petrol. Again: if you’re using regular unleaded, you may want to try premium unleaded. If you’re already using premium unleaded or lead replacement petrol, high-octane petrol may help.
  
• You have a classic car originally designed for 98 RON petrol, but which was re-tuned to be able to use lower octane fuel — resulting in decreased performance. If you decide to use one of the high-octane fuels all the time, you can tune the engine back to the original settings at original performance.

* Must: Understand What Is Knocking

Knocking is the sound caused if fuel isn’t burned smoothly in a car’s engine. In ideal conditions, the spark plug creates a flame that travels across the cylinder, burning the fuel/air mix and steadily building up pressure. If part of the fuel/air mix instantaneously self-ignites before the flame reaches it, the pressure rises rapidly, causing a knocking or pinging noise. Heavy knocking can cause engine damage.

Knocking is influenced by several factors — for example, the build-up of deposits, hard acceleration in a high gear, high-load driving (uphill or towing) and an out-of-tune engine (wrong spark timing or fuel/air ratio) can lead to increased knocking.

Octane numbers

A fuel’s octane number is a measure of its ability to resist self-ignition when burnt in an engine — or its anti-knock quality.

The octane number is measured under standardised test conditions against reference fuels, one of which is iso-octane (hence the name ‘octane number’). There are actually several octane numbers, depending on the test conditions. Car fuels are described by two numbers: research octane (RON) and motor octane number (MON), with the RON being higher than the MON.

Typical RON values are:

• Regular unleaded petrol: 91
• Premium unleaded petrol: 95
• Lead replacement petrol : 96
• High-octane petrol: 98

Each engine requires a certain octane number to prevent knocking — for example, your car may need premium unleaded rather than regular unleaded petrol. This requirement is measured under worst-case conditions, and takes into account a slight increase over time — for example, due to the build-up of deposits. In less severe conditions, the engine can do with petrol of a lower octane number.

Apart from being less likely to develop knocking, an engine won’t benefit from using a petrol with a higher octane number (for example, it won’t provide more power).

Questions: Are you pumping the correct petrol octane rating for your car to save cost?