K&N intakes are known to add an average of 15 to 25 horsepower to a standard system. Each kit is tested to ensure that the filter and intake pipe are positioned to maximize airflow and power. The numbers may be small, but you can still feel the extra power. The K&N air filter promises to deliver more horsepower, and it does. To demonstrate this, a YouTube series installed the filters on a Subaru Crosstrek and ran several tests on a dynamometer.
With the clean OEM filter, the car produced 160.10 hp and 137.43 lb-ft of torque, with a minor increase of 1.85 hp and 0.18 lb-ft. The aftermarket CarQuest filter was surprisingly better than the clean OEM filter, producing 164.3 hp and 142.5 lb-ft of torque. Finally, the K&N filter was installed, resulting in 164.42 hp and 142.53 lb-ft of torque - 1.1 hp and 1.71 lb-ft more than the cheap aftermarket filter. The YouTube series also tested each filter's acceleration with a VBox to see if any data learned from the test bench translated into the real world. The original new and dirty filters were almost identical in their sprints (9.01 seconds from 20 to 60 mph and 3.61 seconds from 45 to 60 mph).
However, aftermarket air filters improved that performance. I have used the K&N filter on most of my cars and trucks, and I can attest that it is worth it. I saved money over the life of my truck by not having to buy air filter after air filter. What's more, I removed the screen before the air cleaner box and reset the computer by removing the positive cable for 5 minutes so that it could relearn the new air-fuel mixture. In conclusion, K&N air filters are an easy and quick way to add more airflow, horsepower, and throttle response to your car while still protecting the engine. Although they may not produce huge increases in power, they are still worth it in terms of cost savings over time.