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When I go to the pumps, do I really need the high-performance fuels? What's the difference? My husband tells me to save my money and stick with regular. - Tanis in Halifax

There are reasons to follow the manufacturers recommended fuel type found inside the fuel cap, and in your owner's manual; not only will your car perform as it was designed to do, it will absolve you of any warranty issues if the dealer says you've been using the wrong fuel.

While regular gasoline may be suitable for many new vehicles, a number of higher-performance cars either recommend or require a fuel with a higher octane rating.

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"The reason a manufacturer recommends a certain fuel is that they're claiming a certain performance level with their vehicle and, to get what they claim, you've got to put in the fuel they recommend," says John Broek, a Porsche Goldmeister Technician in Vancouver.

So what exactly is the difference with higher-performance fuel?

They may look and smell the same, but two different fuels will be much like two cakes baked with different quality ingredients. There are many different ingredients that go into a fuel - from aromatics, to ethanol, and a whole list of additives such as injector cleaner.

"The octane number is a measure of a gasoline's ability to resist knock or pinging noise from an engine. A car's octane 'appetite' may increase with age. Over time, deposits can accumulate in your car's combustion chamber. In older vehicles, knock may be accompanied by engine run-on. If you hear knocking, a car owner should have their engine checked and/or use a higher-octane gasoline," says Chevron Canada spokesperson Deidre Reid.

Similarly, driving conditions can increase a car's octane requirements. "Any of the following can increase the octane level a vehicle may require: carrying or towing heavy loads, driving in low-altitude areas, driving frequent short trips, or driving in high temperatures," says Reid.

According to Broek, as long as your car is equipped with electronic knock control, you won't damage the engine by using a fuel grade lower than what the manufacturer recommends - but the performance level will drop. "If it's an older car that doesn't have that feature, however, it could ping and do some damage," says Broek.

A vehicle may run more efficiently on higher-octane fuel, but most motorists may not notice. "If you putt around town and drive like the average person, you'd probably never notice the difference. If you filled your tank with premium fuel and went out on the highway, it may run a little better because the timing would be farther advanced, and it probably will run a little smoother. There may also be a bit of difference in the way it starts in the morning," says Broek. So, does higher octane mean better fuel economy? "In theory there would be a difference. Would you notice? Probably not."

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John Thorne, who runs one of the United Kingdom's largest car-tuning services, disagrees. His company, Thorney Motorsport, has conducted five different fuel tests on 18 different vehicle types over the last five years. "Pretty much consistently amongst all the tests - which cover vehicles from 20 years old up to brand new - generally speaking you have an 8 to 10 per cent improvement in power on any car," says Thorne. "This generally equates to roughly half of that in fuel economy. It's not an exact science, because it depends on the car, but generally speaking we have been averaging between 5-10 per cent improvement in fuel economy when we had an 8-10 per cent improvement in power. Whether you're doing more freeway driving or town driving, it's that big of a difference."

Essentially, Thorne says, with higher-octane fuel you'll see a bigger effect on high-performance cars, and a reasonable effect on smaller cars.

Not convinced? "I tell people: don't believe me, go and try it yourself. Empty your tank completely so the light comes on, fill up, and reset your [odometer] Do three full tanks on your regular fuel, and see how many miles you did on those three tanks. Once you've finished, do three tanks on higher-octane fuel, and see how many miles you get. Worse-case scenario, all you've done is cost yourself a few dollars; best-case is you save money and the planet," says Thorne.

Since the jury is still out - you'll have to test it for yourself. The consensus on performance, however, is that your vehicle will run better no matter what make or model. If you enjoy getting maximum performance from your car, and you find your fuel economy does improve, using performance fuels seems like the way to go - just check with your manufacturer before you tell your husband.

E-Mail Ask Joanne at

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About the Author

Joanne Will is based in Toronto. She has been a regular contributor to The Globe and Mail since 2009. In 2014, she was a Knight-Wallace Journalism Fellow at the University of Michigan. More

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