How Petrol Octane Ratings Work

If you’re scratching your head wondering which number petrol to put in your car, don’t overthink it. Just Google the manufacturer’s recommendation and run with that. If you’re curious about what those numbers mean in a practical sense, check out this video.

Car YouTuber ChrisFix seems to be branching out from his usual “how to repair something” content into somewhat broader topics, and this video explains why higher octane gasoline isn’t necessarily better and it doesn’t store more energy.

Octane ratings are about knock resistance, not explosive power. The higher the octane rating, the less likely the fuel is to prematurely detonate. But as long as your engine’s running correctly, that’s only a possibility if the engine’s designed a certain way. Typically, with a turbocharger or very high compression.

ChrisFix also explains why the octane ratings on European gasoline pumps often seem higher than American ones – they’re just using a different scale over there. The juice flowing through the pump is largely the same.

The second half of the video focuses on detailing the residue that low-quality petrol can leave behind, but as far as practical advice there, all you really need to know is that “Top Tier” branded fuels are generally going to have the most detergent characteristics. In other words, if the petrol station is a brand you’ve heard of, you’re probably OK. Exploring the different proprietary additives that each petrol brand adds will have to be a project for another time.

But the real reason I wanted to share this video is the cutaway animation at about the three-minute mark. There, you can see a very clear illustration of the combustion process: fuel and air in, fuel and air compressed, fuel and air ignited, exhaust out. That’s compared to an engine experiencing detonation–the fuel exploding too soon, basically.

Even if you already knew that the clip is still a neat way to experience it. It’s not like you can watch your engine run from the inside-out at a low speed in real life, anyway. Hopefully, you either learned something here or found yourself a super-simple explanation to send to your friends when they ask if they need to run premium fuel.

This story originally appeared on Jalopnik.


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