The
ONLY purpose for higher octane in gasoline (petrol) is to prevent detonation, also known as the unintended explosion of the compressed fuel-air mixture in the cylinder, before it is intentionally ignited by the spark plug. This includes a phenomenon known as "knocking," which is why octane is sometimes called "anti-knock."
Feeding an engine a lower octane fuel than that demanded by the manufacturer (e.g, using mid-grade when the user manual tells you to use only premium) may reduce horsepower and/or damage your engine.
Using higher octane fuel than your user manual recommends (e.g., using premium when your manual says regular is fine), will not increase power, fuel economy, or any other positive trait in any meaningful manner, and most certainly, it will not provide sufficient benefit to compensate for the significantly higher fuel cost. That's just a plain fact.
The only time when using a higher octane fuel give you a benefit, is when you run it in an engine that was specifically designed to
need that extra octane. Otherwise, it's a waste of the consumer's money.
In actual research using a variety of vehicles (various number of cylinders, base horsepower, automatic and manual transmission, brands and models), if you use a higher octane rating than what your vehicle needs, tests showed some vehicles actually got a slight reduction in power and/or fuel economy, and some got a miniscule increase.
Even so, Internet myths will persist, such as:
- Higher octane gets you better MPG, HP, torque, longevity, fewer repairs, lower emissions, etc.
- Nitrogen in your tires provide some benefit
- You can bolt on a mail-order fuel saver that'll give you better fuel economy
- etc.
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