The K&N RU-5040 is a reusable universal clamp-on intake filter built on K&N's cotton gauze platform, aimed at builders who need a 3.5-inch flange rather than a full cold-air kit. Its published dimensions are a 3.5-inch flange, an 8.5 x 5.25-inch base, a 6.25 x 4-inch top, and a 5.5-inch height, with an oval straight shape, and the manufacturer lists overall filter efficiency at up to 99%. This is a K&N High-Flow Original oval universal cone filter, so it's a drop-in option for custom intake tubes.
Compared with a disposable paper element, the RU-5040 trades recurring replacement cost for a wash-and-oil cycle. The manufacturer describes multiple layers of premium cotton gauze treated with a tacking agent, and says the media is designed to increase horsepower and acceleration. The flange is also forgiving: it can be stretched up to 1/16 of an inch (1.5mm) to fit in-between sizes. Owners searching for a 3.5 inch flange universal air filter for a track car, an oval tapered intake upgrade, or a reusable K&N air filter swap will find it a practical match.
The manufacturer sells it as a universal clamp-on filter, so fitment depends on your intake rather than a listed vehicle. Measure your inlet against the 3.5-inch flange and the 8.5 x 5.25-inch base before ordering.
The manufacturer states that K&N universal air filters are washable and reusable. Re-oil it with the specified amount after cleaning.
The manufacturer lists overall filter efficiency at up to 99%.
This is a clamp-on installation, so basic hand tools are usually enough. Slide the rubber flange over the intake tube and secure it with a hose clamp; K&N's own cold-air kit instructions call for installing the filter onto the adapter and securing it with a hose clamp. Seat the flange fully and tighten evenly, since over-tightening can distort the rubber. Check that the base clears nearby fender, bracket, or engine components. Because the part is universal, you may need to adapt the intake tube length or clamp position for your engine bay. After washing, re-oil the media lightly and let it dry before reinstalling.
