Air filters are one of the most straightforward and quickest components to upgrade for an aftermarket part, and many companies promise that their design will increase power, torque, and improve acceleration. In reality, it makes such a big difference that the simple process of redirecting the filter to extract cooler air is good for a power gain of about 5 to 20 ponies in most cars. It could even improve fuel efficiency and will likely make the engine sound better as well. Because vehicle makes, models, and engine sizes vary widely, along with vehicle condition and environmental factors, power gains also vary with individual applications and vehicles.
However, K&N intakes generally add an average of 15 to 25 additional horsepower compared to a standard system. Each kit undergoes significant testing to help ensure that the filter and intake pipe are positioned to deliver large increases in airflow and power. Dyno test charts can be viewed on individual product pages, which can help provide an estimate of the amount of power increase you can expect from a system upgrade. To test this out, Fenske installed four different air filters on his Subaru Crosstrek: one is the original air filter that came with the car after thousands of miles, the second is a new Subaru OEM filter, the third is a low-cost CarQuest replacement, and the final part is a K&N air filter. Without further ado, the dirty OEM air filter allowed the car to produce 158.25 hp and 137.25 lb-ft of torque.
The new Subaru OEM filter produced 159.36 hp and 138.36 lb-ft of torque. The aftermarket CarQuest filter was truly surprising, as it performed better than the clean OEM filter even though it cost less - it generated 160.37 hp and 139.37 lb-ft of torque. Finally, the K&N filter was installed, which allowed the engine to produce 164.42 hp and 142.53 lb-ft of torque. This was the best performing filter, but it only created 1.1 hp and 1.71 lb-ft more than the cheap aftermarket filter. The aftermarket filter improved performance (9.01 seconds from 20 to 60 mph and 3.61 seconds from 45 to 60 mph), but Fenske wondered if it actually filters less overall as well. Paper filters exhibit a principle called surface charge since dust accumulates only on the surface of the filter media - as dust accumulates on the surface of the disposable filter and blocks openings in the medium, the filter will normally become increasingly restrictive to air flow over time. K&N intakes protect your engine by using a specially designed, premium, high-flow air filter that can retain significantly more dirt and particles per square inch of material than an average paper filter.
The premium air cleaner included in a K&N intake system helps increase airflow by up to 50% compared to a traditional disposable paper air filter, and the intake tube is designed to flow a large volume of oxygen-rich air without the excessive baffles and diminishing components that many factory systems have. In conclusion, K&N filters promise to deliver more horsepower - and they did! The Crosstrek produced 164.3 hp and 142.5 lb-ft of torque with this upgrade - plus improved fuel efficiency and engine sound.