According to the age-old claim, a higher RON octane rating delivers better performance and fuel efficiency.
When challenged to prove that claim, supporters of the higher RON octane rating fuel will point to the fact that high-performance cars use them to achieve better performance.
Are they correct? Let’s find out…
RON / MON Octane Rating : A Quick Primer!
RON is short for Research Octane Number. It is a ROUGH indicator of the maximum compression ratio at which the fuel can burn without spontaneously detonating.
You don’t want your fuel detonating because that damages the engine, while greatly reducing performance and fuel efficiency.
RON is actually just one of TWO octane ratings used to measure the fuel’s ability to withstand spontaneous detonation in the engine. The other one is MON (Motor Octane Number).
The RON rating is based on a low engine load, while the MON rating is based on a high engine load. A fuel’s MON rating can be up to 10 points lower than the RON rating.
Octane Ratings In Asia, Europe And US
In Asia and Europe, the number you see at the petrol stations are RON numbers. In the United States, they use the average of the RON and MON numbers using the formula of (R+M)/2.
In other words, fuel with a RON of 95 and a MON of 85 will be listed as RON 95 in Asia and Europe, but 90 octane in the United States.
This doesn’t mean that the fuel in America is of a lower RON rating or performance. They are the SAME FUEL. It’s just how the SAME octane numbers are reported.
Asia and Europe only use the RON rating, while the Americans use the average between the RON and MON ratings.
RON ≠ Energy Density
Petrol (or gasoline to Americans) have an energy density (or specific energy content) of about 42.4 MJ/kg. That is how much energy is in the fuel, not how much it delivers.
70-75% of that energy is lost as heat generated during the engine combustion, leaving only 20-30% of that energy to actually move your car.
The energy density does NOT change with the RON or MON octane rating. RON 97 fuel has the SAME energy density as RON 92 fuel.
Energy Density Varies Slightly With Fuel Blend
The energy density, however, can be higher or lower by up to 4%, depending on the fuel blend used by the refinery, and regulations set by the country.
In some countries, the blend changes with the season, yielding slightly better or poorer performance and fuel efficiency with a corresponding increase or reduction in pump prices.
This has nothing to do with the RON or MON octane rating of the fuel, just its blend. You can have a denser fuel blend with a low octane rating, and a lighter fuel blend with a high octane rating.
Higher RON Rating = Better Performance?
If you drive a sports car, it will likely use a high-compression engine. The high compression delivers more power and better fuel efficiency by stuffing more air into the combustion chamber.
However, such high-compression engines require higher octane fuels. Not because they have more power, but because such fuels will not spontaneously detonate from the high compression pressure.
In such sports cars, you will usually find two RON numbers – a minimum octane rating, and an optimal or recommended octane rating. The Audi RS4 Avant, for example, requires a minimum of RON 95 but works best with the RON 98 fuel.
For maximum power and fuel efficiency, Audi RS4 drivers should use the RON 98 fuel. Using the RON 95 fuel will result in a slight reduction in power and fuel efficiency at high engine loads.
This is NOT because the lower octane fuel is less powerful, but because the RS4 engine will change its timings slightly to prevent the lower octane fuel from spontaneously detonating at high engine load.
The Audi RS4 can actually use even lower RON fuels – as low as RON 91. However, this will result in reduced performance and the car should be driven gently.
Remember that the RON number is based on low engine loads. At higher engine loads, you will need a higher RON rating to avoid engine knocking.
Not all sports cars require high octane fuels though. This is a popular misconception.
Take the Nissan 370Z, for example. It only requires RON 95 fuel to perform optimally and can run on RON 91 fuel in an emergency. Again, when using RON 91, it should be driven gently to avoid engine knocking.
Most other cars, however, will only list a single octane rating, which is both the octane rating they are tuned for and the minimum octane rating you should use.
You can use higher octane fuels, but you will not derive any performance benefit because the engine is not capable of higher compression ratios that would take advantage of the higher octane.
Unless your car manufacturer specifically tells you to use a higher octane rating, you are just wasting your money buying a higher octane fuel. It will not make your car go any faster.
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Heavier Fuel Blend = Better Performance
Now you hit the nail on the head! Higher octane will not give you more power, but a denser fuel blend will.
This is because a heavier fuel blend has a higher energy density – that means every combustion cycle yields more energy.
Fuels with higher octane ratings may use a denser fuel blend, although this is not necessarily the case. It all boils to marketing, because the fuel blend only changes up to 4% either way.
That’s a maximum variance of 8%. Generally, the variance is much smaller. Take a look at these BP fuel energy density figures, courtesy of Car Bibles :
|Fuel Grade||Energy Density||Difference|
|BP Regular||32.53 MJ/L||Baseline|
|BP Premium||33.08 MJ/L||+ 1.7%|
|BP Ultimate||33.28 MJ/L||+ 2.3%|
Even the most expensive BP fuel has a mere 2.3% boost in energy density over its cheapest regular fuel. Even that has limited effect because remember, 70-75% of the energy is lost as heat.
So what you would probably get from using BP Ultimate is a 0.7% boost in power (30% of the 2.3% higher energy density).
A heavier fuel blend, therefore, is mainly a marketing gimmick. By using a heavier blend, companies get to honestly tout better performance for their higher octane fuels, which have much higher profit margins.
You will undoubtedly enjoy better performance, just not as much as you think you are getting.
Higher RON / MON Rating = Better Fuel Efficiency?
The short answer is – NO. As we pointed out before, the RON / MON octane rating of a fuel is not an indication of how much energy is in it (energy density), or how efficiently it will burn in the engine.
The RON / MON octane rating only indicates how resistant the fuel is to spontaneous detonation when it’s being compressed in the engine’s combustion chamber.
That said, we must point out that the use of fuels with the proper RON / MON octane rating is critical in preventing your car from suffering from poor performance and fuel efficiency.
If you use a lower RON octane rating than is recommended by the car manufacturer, engine knocking may occur. The modern engine will detect that and retard the ignition timings to prevent or reduce the amount of engine knocking. Take a look at this excerpt from a Porsche manual.
However, retarding the ignition timing reduces power and fuel efficiency. How much you lose in power and fuel efficiency depends on how much knocking occurs and how much the timing changes to compensate.
Generally, the greater the discrepancy in RON octane rating and the harder you work the engine, the more you lose in power and fuel efficiency.
In other words, there is no benefit in using a higher octane fuel, but it pays to keep to the car manufacturer’s recommended octane rating.
Higher RON Octane Rating For Higher Altitudes
A fuel’s RON octane rating is affected by atmospheric pressure. It actually drops by 1 for every 600 m or 2,000 ft in elevation.
Many people ignore this because they don’t live in high altitude communities, but this can make a real difference in performance and fuel efficiency for those who do.
La Paz in Bolivia, for example, is 3,640 m (11,942 ft) above sea level. If your car uses RON 95 fuel and you pump it full of RON 95 fuel at sea level, your car’s power and fuel efficiency will drop as you near La Paz.
That RON 95 fuel you pumped at sea level would only have an octane rating of RON 89 in La Paz.
By the time you reach La Paz, your car would really be running on RON 89 fuel, and the engine would be retarding its ignition timing to compensate for the lower atmospheric pressure.
Higher RON Octane Rating Myth : A Summary
Before you decide if you really need a fuel with a certain RON octane rating, please take out that nicely-printed manual that came with your car and open it up. Look for the page that talks about its fuel recommendation and READ IT.
Note what it says about the car’s minimum and recommended RON octane rating. If only one octane rating is mentioned, consider that as both the minimum and recommended rating for your car.
- You will achieve maximum performance and fuel efficiency if you use fuels that meet the recommended RON octane rating for your car.
- Using fuels with higher RON octane ratings won’t harm your car, but it won’t give you any additional benefits either.
- Using fuels with RON octane ratings that are between the minimum and recommended ratings for your car will give you optimal performance and fuel efficiency at low to normal loads, but will not achieve the engine’s full potential in performance and fuel efficiency at high loads.
- Using fuels with RON octane ratings that are lower than the minimum rating for your car will reduce power and fuel efficiency.
- Altitude matters, so make sure you use fuels with higher RON / MON octane ratings at higher elevations.
We hope this article will finally put to rest the myth that a higher RON / MON octane rating means better performance and fuel efficiency.
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