The K&N RE-0870 is a round, tapered universal clamp-on air filter built on K&N's oiled cotton gauze element. It has a 4-inch flange inlet, a 6-inch base, and a 9-inch overall height, with a rubber top. Compared with a disposable paper element, this filter can be washed, re-oiled, and reused, so you are paying once instead of buying replacements. Its molded rubber flanges absorb vibration and can be stretched up to 1/16 inch (1.5 mm) to fit between standard sizes, which makes it a practical choice for custom intake tubing, racing builds, and non-standard applications where a direct-fit filter isn't available. Search terms this filter matches include K&N RE-0870 4 inch flange conical filter, universal clamp-on cotton gauze air filter, reusable 9 inch tall air filter, and washable custom intake filter. Installation is a clamp-on job that involves sizing the flange to the intake tube, securing it with the included stainless hose clamp, and oiling the media before use. The filter is pre-oiled, but the manufacturer's re-oiling guidance should be followed when you clean it.
The product is designed for a wide range of applications, including racing vehicles, generators, snowmobiles, and tractors, so confirm your intake tube's inside diameter and tapered-body clearance before ordering. Measure the intake opening first, since the flange is 1.75 inches long and the 4-inch inlet must match or land within the stretch range of the rubber. Owners on user forums commonly check whether the flange will seat fully on the tube before tightening the clamp, and that step prevents unfiltered air from bypassing the element. Because the filter is not designed for every vehicle, fitment should always be verified against your specific intake setup.
The manufacturer states that the molded rubber flanges can be stretched up to 1/16 inch (1.5 mm) to fit between sizes. Check the intake tube diameter before purchase, because the stretch range is limited.
Yes. The manufacturer describes the filter as washable and reusable. Owners on user forums generally clean the element and re-oil it according to the manufacturer's instructions, and the re-oiling amount should be confirmed with the manufacturer before use.
This is a clamp-on filter, so installation is a basic DIY task. Confirm that the 4-inch flange seats fully on the intake tube, then secure it with the stainless steel hose clamp included with the filter. Because the flange is malleable, a slight stretch can help it fit a tube that falls between standard sizes, but do not overstretch it. Check that the clamp is tight and that there are no gaps where unfiltered air could enter. Most of the work involves measuring and fitting, rather than specialty tools.
