K&N Street Metal Air Intake Systems for Harley Davidson motorcycles increase power by replacing the restrictive stock OE air cleaner with an oversized K&N High-Flow Air Filter and a cast aluminum high-volume aluminum housing. This K&N high-flow air intake system gives your Harley an aggressive appearance while providing a significant increase in airflow, resulting in more power. Some K&N air intakes are not legal for sale or use in California and other states adopting California emission standards while others are 50 state legal. View the vehicle applications to determine the legal status for each vehicle.