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Custom Assemblies > Intake System-Harley Davidson

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RK-3909-1
 
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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.

[More Information on High-Flow Air Intake for Harley-Davidson Motorcycles]
  • Designed to increase horsepower & torque
  • Dyno-tuned velocity stack
  • Washable and reusable
  • Excellent air filtration
Available Information
Installation Instruction Sheet
RK-3909-1 Vehicle Applications
Dyno Chart - 2010 Harley Davidson Fat Boy 96ci - 9.59hp
Dyno Chart - 2006 Harley Davidson Road King 88ci - 6.05hp
News Story - Harley-Davidson Softail, Touring & Dyna Motorcycles Get Extra Power with K&N Assembly


Part RK-3909-1 Product Specifications
Product Style: Motorcycle Intake System
Estimated Horsepower Gain: 6.05 HP @ 5206 RPM
Street Legal In All US States: See Application Link Below
Air Filter Color: Red
TUV Approved (Europe): No
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
Color: Red
Filter Material: Cotton Gauze
Inlet Diameter: 2.25 in (57 mm)
Intake Pipe Ports: All intake tube ports needed for the specified applications are included
Mass Air Flow Sensor Adapter Included: No Mass Air Flow Sensor Adapter Required
Mounting Hardware Included: Yes
Neck Flange: 2.25 in (57 mm)
Overall Height: 1.688 in (43 mm)
Replacement Filter: E-3972
Size: 7 Inch
Style: Oval
Top Material/Finish: Black Powder Coated
Top Style: Metal
Vacuum Tubing Included: No
Weight: 3.3 lb (1.5 kg)
Product Box Length: 11.75 in (298 mm)
Product Box Width: 9.5 in (241 mm)
Product Box Height: 4.88 in (124 mm)


Horsepower gains based on similar vehicle dynamometer test. Results will vary.


Customer Feedback      Be the first to review part RK-3909-1

Dear sirs:

All I can say is most people won't believe this but then it's their loss...in miles per gallon that is. I Own 2 Harleys, a 1979 HD Sportster that several years ago I put a K&N air filter on and felt like it doubled it's performance, and a 1999 FLSTF Fat Boy. I didn't rest there, as a year ago I put a K&N on my 2001 Dodge Ram Quad cab Cummins turbo diesel and also felt the increase in performance not to mention the scream of that turbo that I had never really heard from the factory.

Recently two of my buddies and I went on a motorcycle trip to Stecoah, N.C. Before going on the trip I changed all my fluids and serviced the whole bike. I decided to buy a K&N air filter and pitch the stock one. They were riding a 2003 Honda Goldwing, a 2005 Harley Davidson Roadking and I took my 99 Fat Boy. Prior to installing the K&N my Fat Boy got between 40 & 43 MPG. As we went from fuel stop to fuel stop my mileage was as follows: 43 MPG, 47 MPG, 46 MPG, 48 MPG and 52 MPG EVERY tank after that. My buddies only mustered 44 -46 MPG. Most people would ask what about the weight and the speed. Well both my saddle bags were packed, I had a bag with 20 lbs. on my luggage rack, plus my TBags weighed in at about 50 lbs. The weight we carried was all about the same. The motorcycle weights were different, but not enough to warrant the major difference in MPG. Also mine is carbureted and theirs are fuel injected. As far as the speeds, we were cruising on the interstate at 70 to 80 MPH through a whole fuel run which was about 200 miles. Even when I was on the tail of the dragon, which is 318 turns in 11 miles, my mileage stayed at 52 MPG. All I can say is after over 1700 miles on that trip the K&N definitely paid for itself with the increase of 9-12 MPG.

So everyone has a choice. you can pay at the pumps or spend that money on the LAST air filter you will EVER buy.
Ronnie E., Glen Rock, Pennsylvania
All of my vehicles including my Harley Davidson have K&N Filters installed. They perform without equal.
Robert W.Garcia Sr., Paradise, Texas
I have used K&N products for several years as a ship's engineer. I am now retired and still own the 1988 Harley Davidson FLST I bought new in '87. I also am still using one of the first Screamin Eagle CV carbs. No one makes the correct air filter, so I went back home to K&N for a universal filter that I knew would not only deliver the air flow necessary but would look good as well.
John Sayers, Lecanto, Florida