The K&N RD-0720 is a round, straight, clamp-on universal filter built on cotton gauze media, with a 2.5-inch flange inside diameter, a 3.5-inch outside diameter, and a 6-inch body. Its molded rubber flanges dampen vibration and seal to the intake, and the manufacturer says the flanges can be stretched up to 1/16 of an inch to fit in-between sizes. Compared with a disposable paper element, you can wash and reuse it, which spreads the cost over many service intervals. The manufacturer presents the design as a way to increase horsepower and acceleration, but no power figure is confirmed for this part, so treat that as a design goal rather than a measured gain. Universal fitment is the main reason to choose it over a fixed-diameter stock replacement: it is designed for intakes with varying angles or offsets, and the manufacturer lists uses including racing vehicles, generators, snowmobiles, and tractors.
For a street vehicle, confirm emissions status before buying, especially in California and other CARB states. Owners on user forums with other K&N clamp-on filters describe mixed mounting results: some people have mounted a filter with just the hose clamp without problems, though one owner recommended a bracket instead. Another owner warned that nuts and washers on a homemade bracket came undone and were sucked into the intake, so lock your hardware. Expect some tuning work: one forum owner had to retune the idle after switching to a K&N filter. Shoppers searching for a K&N universal clamp-on air filter with a 2.5 inch flange, a round straight carburetor air filter, or a reusable cotton gauze air filter with 6 inch height will find this size fits that search.
The manufacturer describes the flange as adjustable within a small range, up to 1/16 of an inch, so measure your inlet diameter before ordering rather than relying on the stretch to close a larger gap.
The manufacturer lists the filter as washable, with a re-oiling amount of 0.52 oz. Use the manufacturer's cleaning guidance for the correct products and steps.
Owners on user forums report that some people have mounted it with just the hose clamp and they seemed to have had no problems, while others prefer a bracket for added security.
This is a clamp-on installation, so it is a straightforward job rather than a full airbox swap. Use hose clamps sized to your inlet, and if you fabricate a bracket, check that it still seals against the intake, since owners on user forums have reported leaks from brackets that don't seat properly. Use locking hardware and inspect it after the first few drives. Plan for a brief rich-running period while excess filter oil burns off, and expect to retune idle if the engine runs rough. Before installing on a street vehicle, verify emissions legality for your state.
