I’ve been involved in automotive-related jobs for my whole working career, which has included a stint as an auto insurance accident investigator specializing in property damage. In 2005, my career path took me into the fueling industry, where he currently performs retail fuel station testing. Through all of this, Allan has been involved in driver education, including class A driver training, and presently, also works part-time as a CMSP-certified motorcycle instructor. Allan has been a motorcycle rider for over three decades.
Are higher octane fuels more expensive because they are better?
Higher octane fuels are more expensive, so they must be better, right? It really depends. Let’s consider a number of factors:
Is octane an additive?
Many confuse the role of octane with the practices of altering fuel by introducing additives, such as detergents, emulsifiers, and stabilizers. Octane simply means stability. Lower 87 octane is less stable but perfectly suitable for use in most engines.
Where does the octane number come from?
Typically, two different methods are used to determine a gasoline’s minimum octane level, and then those two are averaged together. The lower octane fuels are mostly referred to as regular, while the higher octane fuels are most often called premium or super. The middle octane fuel (89) is commonly a 50/50 blend of the other two.
How does the gasoline get inside my engine?
To better understand the role that octane plays in engine performance, let’s first take a technical look at what an engine will do with its fuel.
The mixture of air and fuel can make its way into an engine in a few different ways. Older engines and some current offerings in the motorcycle market use one or more carburetors. A carburetor uses the engine vacuum to draw ambient air in through its main passageway, called a venturi. As the air flows through the venturi, fuel is misted into the airflow. The pressure increase of the air, now mixed with fuel mist, is determined by the length, diameter, and shape of the passageway it takes to get into the engine. The more pressure it builds, the more efficient the fuel ignition is likely to be. There are several ways to increase the fuel’s pressure on its way into the engine; a longer intake passage, supercharging, and turbocharging, just to name a few, but in any case, the air/fuel mixture will be further compressed inside the engine before it is ignited. Many modern motorcycles, and almost all current cars, use fuel injection to mix air and fuel and get the mixture into the engine. Fuel injection is simply more precise and more efficient and the fuel system is typically under higher pressure than its carbureted cousin.
What happens if I use a fuel octane that is too low?
Inside the engine is where the stability of the fuel really matters because the ignition must happen at a specific instant for the engine to perform at its peak. If the fuel is unstable, it may ignite just from the heat generated by the compression process and some of the explosive power intended to drive the piston downward will be working against the piston, costing an engine power instead. The compression is determined by the difference in the cylinders’ volume from one end of the travel (the engine stroke) to the other. The higher the compression, the more likely the air/fuel mixture is to pre-ignite. For higher compression engines, higher fuel stability is needed to avoid that pre-ignition.
What happens if I use a fuel octane that is too high?
Higher octane fuel will never damage an engine where a lower octane fuel will suffice, but it might not provide any benefit either. This brings us back to additives and price points. Higher octane fuels frequently have additives that their lower octane counterparts do not. If your bike only needs 87, and you want additional detergents, for example, you can add an injector cleaner to your tank and have the same benefit, but at a difference of 30 cents per gallon, you may be paying less just to go with the higher octane fuel.
Which octane should I use in my motorcycle?
This was a long way to explain why there is no universal answer to which fuel is best, but it depends on your bike. A manufacturer will have a recommendation of which fuel to use, but no explanation of why. When it comes to octane, I suggest going with nothing lower than your manufacturer’s recommendation. A lower octane fuel than what is recommended may run your bike, but you will likely have a drop in performance or efficiency, and possibly longevity, especially at those higher RPMs.