After plenty of research and personal experience I can say that K&N Air Filters are great (under certain circumstances). K&N advertises that their air filters improve performance and fuel economy as a result. I can tell you that through all my research, K&N stock drop-in high flow air filters don't improve horsepower. The only way to improve horsepower is to add a cold air intake system, if your car does not already have one. Don't be discouraged, an increase in throttle response is noticed with these drop-in filters and the engine idles smoother. I was lucky that my car came stock with a cold air intake from the factory. Okay, so my car already has a cold air intake, but does it improve performance? Probly not, because the cold air coming in already gives the engine a boost in performance by itself even with a stadard paper air filter. Usually performance cars such as Corvettes, Cobras, Vipers, etc. would be the sort of cars that would have an improvment with a drop-in high flow air filter. So why did I get a drop-in high flow filter from K&N? Well, it complements the cold air intake and the new performance muffler I will be getting. In my final opinion the sort of people who should be getting a high flow air filter are race car drivers, performance car drivers, and anyone that wants to squeeze that last drop of performance out of their engine. As for filtering ability, high flow isn't always dirty, but make sure you consult with an automotive expert and/or professional mechcanic to see if it is worth it.
