Air filters are one of the easiest and quickest components to swap out for an aftermarket part, and plenty of companies claim their design will increase horsepower, torque, and improve acceleration.
Do they? Jason Fenske of Engineering Explained is here to answer that question. For the test, he used a Subaru Crosstrek and four different air filters. One is the original air filter that came with the car after thousands of miles, the second is a new OEM filter from Subaru, the third is a low-cost replacement from CarQuest, and the final part is a K&N air filter.
Fenske tested each filter with a dyno run and then measured acceleration with a VBox to see if any data learned from the dyno translated to the real world. Up first was the original air filter, complete with dust and bugs.
The Crosstrek laid down 158 horsepower and 137 pound-feet of torque with the original air filter. Note: Fenske said the dyno measured high since the Crosstrek only makes 148 hp at the crank. However, the test is still valid because it serves as a baseline for the other filters. Fenske explained in the past that dyno numbers may not actually be something to brag about, due to some quirks.
Next up was the clean OEM filter and the car returned 160.1 hp and 137.4 lb-ft. Minor increases with a clean filter, to say the least.
Moving along, the CarQuest filter helped the Crosstrek produce 163.3 hp and 140 lb-ft of torque. The aftermarket filter made more power, but Fenske wondered if it's also actually filtering less in general.
Finally, the K&N air filter promises to deliver more horsepower...and it did. The Crosstrek produced 164.3 hp and 142.5 lb-ft of torque.
With the data on hand, do the minor performance increases from the aftermarket filters stack up in the real world? In short, yes.
Jason measured the 20-60 mph sprint and the 45-60 mph sprint. The latter is to show any top-end performance gains. While the dirty and new OEM filters were nearly identical in their sprints (9.01 seconds from 20-60 mph and 3.61 seconds from 45-60 mph), the aftermarket air filters improved on that performance. The CarQuest filter registered a 20-60 mph sprint of 8.91 seconds and a 45-60 mph time of 3.56 seconds. The K&N was, again, the best of the bunch. 20-60 mph happened in 8.81 seconds, and 45-60 mph took 3.49 seconds.
Yes, the aftermarket performance air filters do work. But, don't expect oodles of extra ponies to suddenly show up when mashing the throttle. Check the video above for more details.