What are Octane Numbers?

June 25th, 2018 by

Pull up to the pump and you’ll be confronted by more choices than the difference between gas and diesel. You’ll also have to choose your octane number — or, if you’re driving a diesel, your cetane number.

Someone pumping Gas

What Do Octane Ratings Mean?

Every type of gas has a “knock resistance.” This measures the amount of compression that fuel can stand before it ignites. The greater the knock resistance, the greater the compression allowed. These used to be rated between 0 and 100, but modern high-octane fuels can go higher.

In general, ratings break down as:

  • 87 for Regular
  • 88 – 90 for Midrange
  • 91 – 94 for Premium

A high-octane fuel is often recommended for performance vehicles since their engines require higher rates of compression.

What Do Cetane Ratings Mean?

Cetane ratings are applied to diesel fuel. We’re now looking at ignition delay instead of knock resistance, but it’s the same kind of principle. The cetane number shows the amount of time it takes for diesel fuel to ignite once it enters the combustion chamber. The longer the delay, the lower the cetane rating.

If you own a diesel, you should know that higher cetane ratings come with improved performance thanks to increased torque across the rev range. Since more fuel is burned, your hydrocarbon emission rates drop.

Do You Need to Worry About Diesel or Gas Numbers?

Most modern vehicles are equipped with computer and air-fuel systems that will optimize engine performance regardless of octane rating. However, this changes when you’re looking at vehicles designed for aggressive performance.

Such models usually use forced-induction systems and higher compression ratio engines, so they generally require high octane fuel. If in doubt, you can always check your owner’s manual to find out what’s recommended.

Gas Station At Night
2018 Honda Accord Driving

Learn More About Fuel Octane Ratings at Valley Honda

Drivers across Naperville, Aurora, Bolingbrook, and beyond turn to the Valley Honda service center when they need to find out about anything from fuel ratings to scheduled maintenance. If you have any further questions or queries, don’t hesitate to contact us today.

Posted in Car Care, FAQs, Maintenance, Tips