The K&N E-3730 is a reusable high-flow round air filter measuring 14" outside diameter, 12" inside diameter, and 4" tall. Its layered, pre-oiled cotton gauze media sits between aluminum wire mesh, and the manufacturer designs it as a drop-in element for the factory air box or a matching 14-inch round air cleaner. Because it washes and reuses, you clean and re-oil it instead of replacing a disposable paper element every service interval.
Why pay more than a stock paper filter or a cheap universal panel? The manufacturer rates this element for up to 99% filtration efficiency while promoting improved airflow and throttle response. It carries a No-Hassle Lifetime Limited Warranty, states that it will not void the vehicle warranty, and is emissions legal in all 50 states, which matters for street-driven track cars. The manufacturer does not publish a horsepower figure for this part, so expect a measurable intake improvement rather than a guaranteed gain. Search terms: K&N E-3730 14x4 round air filter, washable cotton gauze air filter, 14 inch round air cleaner element, 4 inch tall drop-in air filter, cleanable performance air filter.
The manufacturer states that the E-3730 is emissions legal in all 50 states and will not void the vehicle warranty.
The manufacturer specifies cleaning only every 50,000 miles under normal highway driving conditions. The listed re-oiling amount is 2.25 oz (67 ml). Driving dustier roads or running on track will shorten that interval.
The manufacturer lists this element among the 14" round filters its carbon fiber top lid fits. Its 14" drop base and offset flat base plates are designed for carburetors with a 5-1/8" airhorn flange, and the custom plate line also lists 7-5/16" flanges. The manufacturer notes that a drop base will not clear every electric choke, so a spacer may be needed.
On most applications this is a drop-in swap: remove the stock or existing element, confirm the sealing surface is clean, and seat the K&N in the housing following the instruction sheet included with the filter. On a round air cleaner, the real work is matching the base plate and lid to your carburetor's airhorn flange and checking choke clearance before final tightening. Check that the element is fully seated so unfiltered air cannot bypass it, and re-oil only to the specified amount, since excess oil can migrate onto downstream components.
