K&N Custom Harley Davidson Air Filter Assembly
Fits 1999-2012 Softail, Fat Boy, Heritage, Night Train, Rocker & Dyna With 1-5/8" Tall Filter - KNRK-3909-1

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 backplate 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.

• Designed to increase horsepower & torque
• Dyno-tuned velocity stack
• Washable and reusable
• Excellent air filtration

Product Specifications
Estimated Horsepower Gain 6.05 HP @ 5206 RPM
Air Filter Color Red
Air Filter Height 1.625 in (41 mm)
Air Filter Inside Diameter 6.188 in (157 mm)
Air Filter Material Cotton Gauze
Air Filter Outlet Shape Not Flanged
Air Filter Shape Round
Clamp Material No Clamps Required
Clamp Style No Clamps Required
Clamps Included No Clamps Included
Color Red
Filter Material Cotton Gauze
Inlet Diameter 2.25 in (57 mm)
Mounting Hardware Included Yes
Neck Flange 2.25 in (57 mm)
Overall Height 1.688 in (43 mm)
Product Style Motorcycle Intake System
Replacement Filter E-3972
Size 7 Inch
Style Oval
Top Material/Finish Black Powder Coated
Top Style Metal

Application
2012 HARLEY DAVIDSON FLSTN SOFTAIL DELUXE 103 CI - w/1-5/8 inch Tall Filter
2012 HARLEY DAVIDSON FLSTFB SOFTAIL FAT BOY LO 103 CI - w/1-5/8 inch Tall Filter
2012 HARLEY DAVIDSON FLSTF FAT BOY 103 CI - w/1-5/8 inch Tall Filter
2012 HARLEY DAVIDSON FLSTC HERITAGE SOFTAIL CLASSIC 103 CI - w/1-5/8 inch Tall Filter
2011 HARLEY DAVIDSON FXCWC ROCKER C 96 CI - w/1-5/8 inch Tall Filter
2011 HARLEY DAVIDSON FLTRX ROAD GLIDE CUSTOM 96 CI - w/1-5/8 inch Tall Filter
2011 HARLEY DAVIDSON FLSTN SOFTAIL DELUXE 96 CI - w/1-5/8 inch Tall Filter
2011 HARLEY DAVIDSON FLSTFB SOFTAIL FAT BOY LO 96 CI - w/1-5/8 inch Tall Filter
2011 HARLEY DAVIDSON FLSTF FAT BOY 96 CI - w/1-5/8 inch Tall Filter
2011 HARLEY DAVIDSON FLSTC HERITAGE SOFTAIL CLASSIC 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FXSTC SOFTAIL CUSTOM 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FXSTB NIGHT TRAIN 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FXCWC ROCKER C 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FLTRX ROAD GLIDE CUSTOM 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FLSTN SOFTAIL DELUXE 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FLSTFB SOFTAIL FAT BOY LO 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FLSTF FAT BOY 96 CI - w/1-5/8 inch Tall Filter
2010 HARLEY DAVIDSON FLSTC HERITAGE SOFTAIL CLASSIC 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FXSTC SOFTAIL CUSTOM 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FXSTB NIGHT TRAIN 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FXCWC ROCKER C 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FXCW ROCKER 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FLSTN SOFTAIL DELUXE 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FLSTF FAT BOY 96 CI - w/1-5/8 inch Tall Filter
2009 HARLEY DAVIDSON FLSTC HERITAGE SOFTAIL CLASSIC 96 CI - w/1-5/8 inch Tall Filter
2008 HARLEY DAVIDSON FXSTC SOFTAIL CUSTOM 96 CI - w/1-5/8 inch Tall Filter
2008 HARLEY DAVIDSON FXSTB NIGHT TRAIN 96 CI - w/1-5/8 inch Tall Filter
2008 HARLEY DAVIDSON FXCWC ROCKER C 96 CI - w/1-5/8 inch Tall Filter
2008 HARLEY DAVIDSON FXCW ROCKER 96 CI - w/1-5/8 inch Tall Filter
2008 HARLEY DAVIDSON FLSTN SOFTAIL DELUXE 96 CI - w/1-5/8 inch Tall Filter
2008 HARLEY D