Many people have reported that putting higher RON fuel than what your car is rated for makes no difference. We’d like to disagree, and here’s why.
We’re sure you’ve heard it before, whether it’s something you read online on an automotive website or heated discussions among your friends. There is a lot of debate surrounding the effectiveness of using a higher RON rating fuel in your car, even if it is only rated to a maximum of say RON 95 or RON 97. In certain respects, this is a pretty accurate line of thinking – and to understand why we disagree with it, let’s examine the logic.
RON stands for Research Octane Number, and it is essentially a standard which fuel is measured by in terms of its stability or volatility, depending on how you look at it. It has nothing to do with the additive packages that some fuel companies will put in, and a higher number usually indicates a more stable form of fuel. The actual chemistry behind it is to do with the length of the chains of fuel molecules but we won’t dive into that – all you need to know is higher RON = more stable fuel.
You might wonder what fuel stability has to do with your engine. Avoiding the nuances and complexities of engine operation, one important thing to know is that when your engine fires its spark plugs it is known as ignition timing advance, or retard. This refers to the number of degrees before or after a piston hits absolute top dead centre, and generally it is known that advancing ignition timing (firing the spark plug earlier) leads to producing more power and torque.
The downside is that advancing the ignition can result in detonation, or uncontrolled combustion – colloquially known as knocking or pinging. It’s a rattle-like noise you sometimes hear with older taxis that run on LPG or NGV, and in essence it’s very bad for the engine. Mild knocking at lower engine speeds is common, but knocking at higher engine speeds and hard throttle can be fatal for the engine.
Because of the ever changing conditions that the car is in as well as different fuel qualities and blends, most modern cars run something known as a knock sensor that monitors the frequency and severity of knock events. If the engine control unit (ECU) detects a fair amount of knock, it will automatically retard the ignition timing in order to protect the engine from harm. The amount of timing which an ECU can advance or retard is still a fairly limited range, and sometimes due to the mechanical design of an engine there is still a minimum RON rating required.
With all of this in mind, you can start to understand why there is a belief that higher RON rating fuel doesn’t do anything for an engine that generally can’t take advantage of it – because of the limited range of spark advance, and mechanical limitations. You will see dyno charts and testing data that supports this hypothesis, but these are all lab controlled tests that don’t necessarily reflect what happens in the real world.
Perhaps the simplest situation you may see this theory fall apart is after sitting in a long traffic jam. When a lot of hot air stays stagnant in the engine bay, such as at a standstill, there’s a phenomenon known as heatsoak where various components in the engine bay get hot and stay hot. This in turn heats up any air at that the engine receives, and hot air increases the risk of knocking. To avoid damage, once again the ECU will start retarding ignition timing and this is why you sometimes feel as though your car feels a little weak after sitting in a traffic jam.
If you run a higher RON rating fuel, the ECU does not have to start retarding timing as soon and in turn can maintain the level of power and torque that you expect with your car. Of course eventually that higher RON fuel isn’t going to help, but if it can retain even a few degrees of ignition timing the effects of heatsoak from sitting in traffic aren’t quite as noticeable.
So perhaps what people need to understand is that running a higher RON doesn’t necessarily give you MORE power, but it lets you run at the maximum possible power under a wider variety of conditions. For other reasons, higher RON fuel also lets the engine run a little leaner on fuel which in turn helps to make your car more fuel efficient – and depending on your usage, it may even make more financial sense to run a higher RON fuel.