Performance air filters are billed as a cheap and easy way to add horsepower to your car, but do they really work? Engineering Explained wanted to find out so they pitted standard OEM filters against a low cost aftermarket filter and a K&N performance filter.
To conduct the test, the YouTube series installed the filters on a Subaru Crosstrek and then made multiple runs on a dynamometer. This allowed them to determine the horsepower and torque changes attributed to each filter. They also used a VBOX to measure real-world acceleration changes.
Without further ado, the dirty OEM air filter enabled the car to produce 158.25 hp and 137.25 lb-ft of torque. When the clean OEM filter was installed, the dyno showed the car produced 160.10 hp and 137.43 lb-ft of torque – a minor increase of 1.85 hp and 0.18 lb-ft.
The aftermarket CarQuest filter was actually kind of surprising as it did better than the clean OEM filter despite costing less. According to the dyno, the filter enabled the engine to produce 163.32 hp and 140.82 lb-ft of torque. This is 3.22 hp and 3.39 lb-ft more than the clean OEM filter.
Lastly, the K&N filter was installed and it allowed the engine to produce 164.42 hp and 142.53 lb-ft of torque. This was the best performing filter, but it was only created 1.1 hp and 1.71 lb-ft more than the cheap aftermarket filter.
Those are some pretty small gains, but are they noticeable in real-world driving? The differences between the clean and dirty OEM filters were negligible, but the cheap aftermarket filter did improve acceleration times by approximately 1.2 percent. The K&N filter fared better as acceleration times improved by an average of 2.74 percent.
While it’s clear that non OEM filters did improve performance, there’s a question of whether they are worth it. A quick check reveals a K&N filter for the 2018 Subaru Crosstrek Premium costs $49.99 and that seems a little pricey considering the minor performance gains.