If your car recommends premium gas, should you use it?

You know those car ads you see filling every commercial break of your favorite television show? Look closely and you’ll see a fair number of them touting either a given vehicle’s power output or perhaps the estimated fuel economy figures. There’s usually also a disclaimer stating that a certain octane level or higher is required in order to achieve those numbers. Your car might not require higher octane fuel, but an automaker might recommend you use the more expensive stuff and it’s often related to those power and fuel economy figures. But how much of a difference does that higher octane fuel actually make and is it worth the extra cost required to fill your car with it?

Our favorite explainer of automotive engineering is ready to answer these questions. Jason Fenske has his whiteboard all set up. His plan? To educate us all on the reason for using higher octane fuel as well as discovering whether or not it’s worth the extra expense. This explainer comes after a recent study released by AAA that talks about why sticking to your automaker’s fuel recommendations might not always make smart fiscal sense.

First, Fenkse walks through the three major reasons you want to use premium fuel. With the higher octane fuel you’ll find that an engine is capable of making more power, returning better fuel economy, and avoiding any potential for engine knocking. That last one is less common these days because the computers inside of the engines are extremely smart about adjusting air and fuel mixtures to help prevent such a thing from occurring.

After that it’s time to dive into the meat of the data compiled by AAA. Various vehicles with their various engines were tested on simulated road grades. A 0 percent grade is level ground and the vehicles were tested at 65 mph. A slight incline using a 2 and 4 percent grade was tested using the same 65 mph test speed. Finally, a steeper 6 percent grade was tested with the speed dropping to 55 mph for this portion. These tests were designed to examine the effect of the different fuel grades with respect to fuel economy.

The vehicles tested covered most of the automotive bases. You have a Ford Mustang GT, Jeep Renegade, Mazda Miata, Cadillac Escalade, Audi A3 and Ford F-150. As for engines, you’ll find naturally aspirated V-8s, turbocharged 4-cylinders, an EcoBoost 6-cylinder, and a naturally aspirated 4-cylinder. Each vehicle in the test doesn’t premium, but the automakers all recommend it.

Moving to the results, it’s clear that premium fuel typically results in a fuel economy improvement. The exception during this portion of the testing fell to the Audi A3, which actually saw a slight dip in fuel economy performance. For all vehicles, however, the average improvement isn’t too massive. The largest jump happens for the Cadillac Escalade which saw an average rise of 7.1 percent across all grades of testing.

The next test switches from focusing on fuel economy to eyeing the actual power being produced. Each vehicle was placed on a dyno and the engine was then run to certain RPM levels and the horsepower recorded. This data points occurred at 2,000 rpm, 4,000 rpm, and then a standard full dyno run was recorded. Using premium fuel, nearly every vehicle saw a slight improvement in horsepower. The largest gain this time belonged to the Ford Mustang which averaged 3.2 percent more horsepower on the more expensive fuel.

These rises in fuel economy and horsepower, however, are small. There are some minor exceptions during all phases of the testing, but generally the improvements gleaned using the premium fuel result in very low increases in performance. The jump in cost per gallon, however, is on average 20 to 25 percent more moving from regular to premium fuel. That small jump in performance might not be worth the larger jump in price per gallon.

If you’re using your car for performance reasons or for towing, however, the extra cost might make sense. Also, if your car requires premium and doesn’t merely recommend it, then you should stick to the high test.

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