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RK-3921
$212.99 USD
MSRP $372.99 42.9% Off
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K&N RK-3921

Custom Assemblies > Intake System-Harley Davidson
  • Designed to increase horsepower & torque
  • Washable and reusable
  • Attractive custom look
  • Chrome plated cover
K&N air cleaner assemblies, designed for your Harley-Davidson®, are a remarkable combination of performance and style. They are machined from billet aluminum, luster polished, then chrome plated to complement your show bike. These K&N custom air cleaners fit all touring models. Each K&N air cleaner comes complete and ready to use, including mounting bracket kit with nothing else to buy.

Product Specifications

Air Filter ColorRed
Air Filter Height2.25 in (57 mm)
Air Filter Inside Diameter6.125 in (156 mm)
Air Filter MaterialCotton Gauze
Air Filter Outlet ShapeNot Flanged
Air Filter ShapeRound
California RestrictedNot legal for sale or use in California
Clamp MaterialNo Clamps Required
Clamp StyleNo Clamps Required
Clamps IncludedNo Clamps Included
ColorRed
Filter MaterialCotton Gauze
Inlet Diameter2.313 in (59 mm)
Mounting Hardware IncludedYes
Neck Flange2.313 in (59 mm)
Overall Height2.5 in (64 mm)
Product Box Height4.5 in (114 mm)
Product Box Length11.56 in (294 mm)
Product Box Width9.5 in (241 mm)
Product StyleMotorcycle Intake System
Replacement FilterE-3336
Size6-8
Street Legal In All US States No
StyleRound
Top Material/FinishChrome
Top StyleAluminum - Flamed Design
TUV Approved (Europe)No
Weight4.5 lb (2.1 kg)

Customer Feedback

Be the first to review part RK-3921
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
K&N has a great web site. I used their vehicle search to find the correct filter for my Harley Davidson 103. I really like the nut on the end of the filter as it makes installation and removal easy, no special tools required. An overall excellent experience Fast shipping as well.

Harold Brooks
San Antonio, Texas
Noticed right away that car had more power. Increased fuel mileage almost two and a half mpg. I always replace the stock filter with a K&N. I have 2 Pickups and 3 cars and a Harley Davidson Street Glide all have K&N filters.

Terry Hagg
Wheatland, Louisianna