K N Performance Air Intake Kit Suitable For Cadillac Cts 3 2 2003 2004 57 3040K&N 57i kit K&N 57i kit. A look under the hood of modern cars makes it clear that the air intake is limited by unnecessary bends and kinks. Air flows the best in a straight line, and is most preferable not slowed down by the filter material. With a K&N air filter you optimize the air supply to your engine. This ensures better performance and a better engine sound. Because of this feature many people call it a power filter. Benefits of a K&N 57i kit: