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In the early 1960s, two motorcycle racers, Ken Johnson and Norm McDonald (K&N) developed a ground-breaking new idea for an air filter. After experimenting with numerous types of filter media, they discovered that an oiled cotton design allowed the filter to not only capture contaminants very efficiently, but also allowed it to be washed and reused, and the original K&N High-Flow Air Filter was born. Five decades later, K&N is still innovating industry-leading filtration technology. In addition to performance air filters, K&N® now manufactures a variety of other protection and performance products, including air intake systems, oil filters & fuel filters, with a reputation for exceptional quality and customer service.

The K&N RK-3930 Air Intake System was designed to get more horsepower from your Twin Cam Harley-Davidson engine. Built around the legendary K&N High-Flow Air Filter, this RK Series assembly includes an innovative powder-coated billet aluminium 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.


  • Increases horsepower
  • Washable and reusable
  • Fits inside stock cover
  • Provides increased airflow


  • Estimated Horsepower Gain: 8.43 HP @ 3700 RPM
  • Replacement Filter: E-3972
  • Air Filter Material: Cotton Gauze
  • Size: 9 Inch
  • Inlet Diameter: 2.469 in (63 mm)
  • Overall Height: 1.875 in (48 mm)
  • Weight: 3.5 lb (1.6 kg)
  • Neck Flange: 2.469 in (63 mm)
  • Mounting Hardware Included: Yes