Why do some cars require premium gas?

Premium gas — that is, gas with an octane rating of 91 or more — is required for some high performance and luxury vehicles. Gasoline with a high octane rating is more difficult to ignite, which helps prevent pre-ignition and knocking in high performance engines. If your car requires premium gas, you can damage the engine if you consistently fill up with regular.

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What is premium gas and octane rating?

Premium gas has a higher octane rating than regular gas. This rating refers to how difficult it is for the gas to experience detonation, a phenomenon that results in fuel burning in the wrong part of the engine cycle. In addition to wasting energy, detonation can damage important engine parts.

This problem, often referred to as engine knock because of the sound that comes from the motor, was more serious in the past. Modern vehicles have onboard computers to regulate the ignition cycle to adjust for lower-octane gas. If your car's engine requires premium gas, you can still cause damage over the long term if you fill with regular.

What cars require premium gas?

If your car needs premium gas to operate safely, it will be indicated on the inside of the fuel filler door and in the car's manual. Cars that require premium gas will typically specify the minimum octane rating necessary, which can be important if you have multiple premium options to choose from. Some cars that need premium only need 91 octane, and others may require 93 octane.

If the owner's manual indicates premium gas is recommended, you can typically operate the vehicle safely on regular gas. Still, you may not reach the performance and fuel economy indicated in the car's specifications. In most cases, the difference in performance is small and something you may not notice during normal driving. If the car is designed for regular — or doesn't specifically say that the car requires premium gas — go with regular. There are no benefits to putting premium gas in a car that doesn't need it.

Learn more about the difference between premium gas vs. regular gas.

Do turbo cars need premium gas?

Not all turbocharged cars need premium gas, but it's a more common requirement among turbos than other kinds of engines, thanks to the way these engines work.

The name turbo comes from the turbine these engines use to inject more air into the air-fuel mixture in the combustion chamber. This generates more power density and increased fuel efficiency, making it a popular design for manufacturers that need to meet emissions standards without compromising power.

Turbocharged engines are becoming more widespread in modern auto production for one simple reason: they deliver more power without sacrificing fuel economy. Still, a turbocharged engine doesn't necessarily mean a fast or high-performance engine. For instance, diesel cars with diesel engines, which are more often used for hauling big loads than for performance driving, often employ turbos.

The trade-off is that turbocharged engines have a higher compression ratio than non-turbo engines. That means they're more prone to detonation and more likely to need premium gas.

Pro tip:

You can easily calculate the difference in running costs for a vehicle that requires premium gas. Just check the difference in price per gallon at your local gas station, multiply that by the number of miles you drive each year, and divide by the fuel economy of your car. For instance, if the price difference is $0.50/gallon, you drive 15,000 miles annually, and your car gets 30 mpg, premium gas will cost you $250 extra each year. Learn how to calculate your annual mileage.

Do luxury cars need premium gas?

Luxury cars may require premium gas if they have a high performance or turbocharged engine. Even if you're not buying a luxury car, more luxurious trim levels for a car may offer engine options that require premium gas. Whether your car needs premium gas or not ultimately comes down to the make and model of your vehicle. Learn more about car insurance for sport and luxury cars.

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