What Are the Differences Between the Gas Grades You Put in Your Car?

Michigan Chronicle › September 09, 2009

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Summary

Engineers discovered a long time ago that an easy way to boost a vehicle's power is to increase the engine's compression ratio, or how much pressure the engine's internals place on the air and fuel inside before igniting it. Cars that require midgrade or high test gasoline put higher pressure on the air and fuel mix inside of their engines.

By now, you're probably getting an idea of what happens when you run low grade gasoline in a vehicle that calls for high test. As the engine compresses the air and fuel mix, it explodes before it's supposed to. This is typically referred to as "ping" or "knock" and can lead to problems.

While jumping down a few grades may save you a buck or two at the station, the loss of fuel economy and potential damage to your engine isn't worth it. Bite the bullet, reach for what your car calls for and squeeze the trigger. If you don't, you'll be sentencing your ride to a slow death one tank at a time.

On the opposite end of the scale, isooctane represents 100 and takes considerably more pressure before exploding. Since straight-run gasoline has such a low octane rating, petroleum engineers incorporate a number of additives and other agents raise the fuel's anti-knock index.