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  • Designed to increase horsepower & torque
  • Dyno-tuned velocity stack
  • Washable and reusable
  • Excellent air filtration
K&N's RK Series was developed to get more horsepower from your Twin Cam Harley-Davidson engine. Built around the legendary K&N High-Flow Air Filter, the this RK Series assembly includes an innovative powder coated billet aluminum back plate that eliminates external breathers and features a built-in, dyno-tuned velocity stack. The result is a significant airflow increase to the engine without sacrificing filtration. This RK Series assembly retains a factory appearance by utilizing the stock air cleaner cover. The RK-3910-1 comes with a larger air filter and longer spacers than the RK-3909-1. 

Product Specifications

Estimated Horsepower Gain 6.05 HP @ 5206 RPM
Replacement Filter E-3972
Air Filter Color Red
Air Filter Material Cotton Gauze
Warranty 1,000,000 Miles/10 Year
Product Style Motorcycle Intake System
Size 7 Inch
Air Filter Shape Round
Air Filter Height 1.625 in (41 mm)
Air Filter Inside Diameter 6.188 in (157 mm)
Air Filter Outlet Shape Not Flanged
CARB EO Number D-269-35/55
Street Legal In All US States See Application Link Above
TUV Approved (Europe) No
Inlet Diameter 2.25 in (57 mm)
Overall Height 1.688 in (43 mm)
Top Style Metal
Top Material Black Powder Coated
Clamps Included No Clamps Included
Clamp Style No Clamps Required
Clamp Material No Clamps Required
Weight 3.3 lb (1.5 kg)
Product Box Height 4.88 in (124 mm)
Product Box Length 11.75 in (298 mm)
Product Box Width 9.5 in (241 mm)
Couplers Included None
Mounting Hardware Included Yes
Neck Flange 2.25 in (57 mm)
Style Oval
Horsepower gains based on similar vehicle dynamometer test. Results will vary.