A cheap way of adding horsepower, though not as much as ricers say they make. Usually add 5-8 on a four pot, 10-15 for a six and 15-30 for an 8. (K&N)
People often install them because they are a much cheaper (however less effective)
alternative to turbocharging or supercharging. (Can also accompany a
turbo and/ or a supercharger)