Page 2 : Heavier Fuel Blend, Better Efficiency, Higher Altitudes, Summary
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 Octane Rating = Better Fuel Efficiency?
The short answer is – NO. As we pointed out before, the 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 octane rating only indicates how resistant the fuel is to spontaneously detonating when exposed to high compression ratios.
That said, we must point out that the use of fuels with the proper octane rating is critical in preventing your car from suffering from poor performance and fuel efficiency.
If you use fuels that have a lower 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 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 Octane Rating For Higher Altitudes
A fuel’s 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.
Mexico City, for example, is 2,240 m (7,349 ft) above sea level. If your car uses RON 95 fuel and you pump it full of RON 95 fuel before heading to Mexico City, you can expect your car’s power and fuel efficiency to drop as you near Mexico City.
That RON 95 fuel you pumped at sea level would only have an octane rating of RON 91 in Mexico City. By the time you reach Mexico City, your car would really be running on RON 91 fuel, and the engine would be retarding its ignition timing to compensate for the lower atmospheric pressure.
Before you decide if you really need a fuel with a certain octane rating, please take out that nice 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 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 octane rating for your car.
- Using fuels with higher octane ratings won’t harm your car, but it won’t give you any additional benefits either.
- Using fuels with 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 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 octane ratings at higher elevations.
We hope this article will finally put to rest the myth that a higher octane rating means better performance and fuel efficiency.
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