Myth Busting: Truth about High Octane

Automotive Industry, like any other, has been maligned with ‘myths’ which are presented and repeated many times that people ultimately start to believe it. Unsurprisingly, many of these myths are related to getting better consumption, increasing the power of the vehicle or some covert aspect of internal combustion engine. Gasoline can be a confusing topic, and it is easy to make assumptions about it that may seem logical, which on closer examination, turn out not to be true. A perfect example of this practice can be seen with octane ratings.

What are octane ratings? In Pakistan, we normally encounter two types of petrol quality on the fuel stations. ‘Regular Plus’, ‘Super’ are some commercial names for Research Octane Number (RON) 87 quality petrol sold in the country and High Octane Blended Component (HOBC) fuel grade which refers to RON 97. I’ll get to the significance of these numbers in a bit.

We tend to associate higher number with better quality. More horsepower, higher torque and more miles out of the fuel are always fancied. This is where the myth of gasoline rating creeps into the picture. Time and again, ‘High octane’ is prescribed to provide better fuel mileage and power as it ‘burns completely’ and locks more energy inside it. These blanket statements are simply not true. In fact, the octane rating for gasoline has nothing to do with the amount of power locked inside of it – it actually relates to just how much a fuel can be compressed before igniting. The higher the number, the less likely it is to ignite under pressure.

Why would you want to put something in the engine that is difficult to burn? To understand the concept of octane rating in the ignition process let us start with a familiar term ‘knock’ or ‘knocking’. When Fuel is sprayed inside the chamber and mixed with oxygen, designers expect it to remain in vapor form until the spark plug lights it up. The timing of this explosion is critical, as gasoline that ignites too early causes ‘knocking’, which reduces engine output and efficiency.

In standard motor, ‘knock’ is rarely an issue because the compression ratio – the pressure that air-fuel mixture is put under in the cylinder – is low enough that the regular octane fuel is sufficient. There is no benefit of running premium fuel in a standard motor, since it will never be able to take advantage of that gasoline’s higher knock resistance. However, more aggressive engine management schemes, especially those found in turbocharged or supercharged vehicles, can turn up the compression to a high level, requiring much higher octane gasoline to avoid knocking.

Fast Facts:

1. You’ll not get extra power or mileage by running premium fuel in the vehicle, unless the owner’s manual states otherwise. If you are getting better mileage or power, convince yourself that it is all in your head and simply a placebo effect.
2. On the flip side, running low octane fuel in an engine built for premium fuel can increase the risk of engine damage and will certainly impact that unit’s overall performance.
3. It is obligatory for all companies oil refineries to produce at least RON 87 petrol by Ministry of Petroleum. All refineries comply with this threshold while Total Oil Pakistan Ltd. sells RON 90 under ‘regular’ grade tag which is a tad higher than the minimum threshold.
4. All locally manufactured cars require RON 87  petrol which consequently means that all locally produced vehicles come under the umbrella of standard motor.
5. High octane grade may be used in small quantity if the vehicle suffers from knocking.