K&N, Twin Cam RK series Street Metal O.S. air cleaner assy

High Flow intake system. Re-use stock air cleaner cover for stock looks. Includes a special backplate; internal velocity stack; built-in breathers; oversized air filter element and hardware. A K&N Dyno test of this RK-series air cleaner assembly on a 2008 Street Bob showed an increase of 6.54 HP@5100 RPM; a 2014 103" Ultra produced an additional 8.33 HP@4670RPM. The K&N RK-Series air cleaner assemblies are truly stealthy air cleaners since the stock air cleaner cover is re-used. Power increase is realized by replacing the stock filter and backplate. A special K&N powder coated aluminum backplate; with Dyno-tuned velocity stack; is required to house the oversized K&N air cleaner element. Built-in breathers replace the stock external breathers. Careful design made it possible to re-fit the stock air cleaner cover for a stock un-touched look. Note: See 900399 for the replacement air filter element.