Why is fuel sold in different grades and what are the benefits of paying more for a premium product?
There are three standard grades for octane fuels in Australia, measured using the Research Octane Number (RON) rating.
- Regular (unleaded) octane fuels (91 RON)
- Mid-grade premium octane fuels (95 RON)
- High-grade premium octane fuels (98 RON)
Higher octane fuels allow engines to run at higher compression levels with additives that clean internal components but they’re not necessary for everyone.
Higher internal engine compression levels generate power more efficiently: think of it like the energy rating on your fridge freezer appliance – the higher the energy rating, the better the efficiency.
But unless an engine is designed accordingly, the benefits may not necessarily justify the expense.
The differences between 95 RON and 98 RON
Fuels such as 95 or 98 RON (octane rating number) have a higher resistance to burn which indicates higher levels of energy available for the vehicle’s engine.According to NRMA motoring expert Jack Haley, on average 95 RON can give around 4 per cent lower fuel consumption than 91, assuming the engine computer adjusts to take advantage of the octane difference.
Using 98 might give 3 per cent reduction over 95, again assuming the computer adjusts the engine parameters.
But fueling an engine with 95 or 98 won’t necessarily open the door to earth shattering performance or extreme levels of fuel economy if the engine is not specifically designed to run on it.
How do premium grade fuels work?
Premium grade fuels simply optimize an engine’s ability to make power through increased fuel density that offer a more controlled burn, reducing engine ping (detonation) and resulting in a smoother delivery of power.
These fuels also contain detergents and boosters which keep components such as valves, pistons and combustion components free of surface varnishes and carbon build-up, which may assist in promoting a longer service life.
Older pre-1990 engines will run quite happily on standard 91 octane fuels, with the exception of certain models requiring super leaded equivalent of 97.
These high-performance engines have compression levels exceeding 10.1:1 that once called exclusively for premium fuels, yet today’s manufacturers are specifying a minimum RON of just 91 for power plants with the same high ratings.
The reason they can do this is Variable Valve Timing (VVT).
What is Variable Valve Timing (VVT)?
VVT combined with sophisticated engine management systems physically adjusts internal compression pressures through advancing or delaying the opening of the engines intake and exhaust valves and spark control.
Under acceleration, an engine’s valve events are delayed while under low throttle cruise they are advanced or held open for longer.
It’s through this type of technology that vehicle manufacturers are able to harness higher performance and fuel economy out of today’s engines while using lower-grade fuel.
So, are premium fuels right for everyone?
With the exception of turbocharged/supercharged models or models specifically recommended by the manufacturer, then the answer is generally no.Engines in today’s cars are nothing like they were 20 years ago – they're far better.
Today’s engines are designed with high levels of efficiency and performance in mind and as a result of VVT technology, today’s highly stressed units are able to thrive on lower grades of fuel as a result.
Vehicle manufacturers design their engines with specific performance characteristics in mind so if you’re unsure which fuel grade your car’s engine requires, simply refer to your owner’s manual or consult your local servicing dealer for further advice.
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