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Fresh Air: Air Filter Buyer's Guide

2011 Polaris Sportsman 850 XP - Engine

An internal combustion engine needs air, fuel, and a spark to produce power. The more air you can stuff into the engine the more power you can potentially make. Getting that air into the cylinder(s) is an important step and not only for maximizing your power output. In order to keep your internal components in tip-top working order and ensure the longevity of your engine, the air you feed it needs to be clear of dust, debris, and other potentially harmful contaminants. That's where an air filter comes into play.

There are many types of air filters for a variety of engines and applications, from the throw away paper filters to reusable, high-flow filters. No matter what brand or type of filter you use, the ultimate goal is to keep a steady stream of clean air flowing into your cylinder(s).

Air Filter Types - Disposable vs Reusable

Air Filter Types - Disposable vs Reusable

The most basic type of air filter is comprised of some kind of paper media that allows air to flow through while trapping dirt and grime. These requite little to no maintenance and aren't cleanable, meaning they have to be replaced regularly - very regularly depending on where you live or the type of riding you often do. While paper filters typically are cheaper to replace, the money you'll initially spend on a reusable filter will eventually flow back into your pocket after a few cleanings.

Reusable filters are offered with a variety of filter media, with the most common being foam, cotton, or a cotton/gauze composition. These filters typically offer more air flow which can equate to more power and better throttle response. They can be cleaned with a simple hand wash or cleaning kit offered by the manufacturer. Most require a filter oil to be applied after each cleaning which helps trap oil and debris.

Foam Air Filters

Uni Filters Foam Air Filters

Foam filters have been around for years and have been very popular amongst power sports enthusiasts for several reasons; they are rather inexpensive, easy to install, reusable/easy to clean, and offer good air flow.

Uni Filters has been offering a variety of filters for more than 40 years, since it's early beginnings, starting with its original Sock Filter. While the Sock filter is still a good product, many people prefer the durability of the 2-Stage Pod Filter. Still comprised with a foam filter media, the 2-Stage Pod offers the added benefit of a course outer pre-filter that can be run dry or oiled depending on conditions.

The Pod filter also has a vinyl mounting flange that helps the filter maintain its integrity over repeated installation/removal. For tight or awkward spaces, Uni offers the 4-inch angled Pod filter with a 15-degree angle on the flange.

K&N Performance Filters

K&N Performance Filters

K&N has been in the filter game for decades, producing not only air filters but oil filters and intake kits as well. With its iconic, red filter media, K&N is easily recognizable by enthusiasts, as well as the average consumer. K&N has made a name for itself with its high-flow filters featuring a pleated, oiled cotton-media. K&N's unique air filter design with its oiled cotton fabric allows high air flow while also trapping dirt particles which then further aid in the filtering process.

The pleated design provides more surface area for more flow/filtration. For dirt bike, street bike, ATV/UTV, cruiser motorcycles and Harley owners K&N offers a variety of universal straight round, tapered round/cone shaped, square, rectangular, and just about any style or shape in between to fit your application and keep your engine happy and healthy.

When selecting one of their universal filters K&N recommends keeping these things in mind:

  • Mounting flange inside diameter: This is the most critical dimension and should be very close to the diameter of the application's inlet flange. The flange will stretch up to 1/8” for those in-between sizes.
  • Filter diameter: This is the outside diameter (O.D.) of the filter. The top size is listed first, then the base size. Always use the largest size filter that is practical for the application.
  • Filter length: This dimension is the vertical length of the filter body only, it does not include the length of the flange, nor does it take into account the taper of the filter media. Always use the longest filter practical, for maximum filtration.
  • Flange angle and/or Length: If no angle is listed in the specifications table, the flange is straight. Any angle listed is in degrees and can be utilized when space is a problem.
  • Flange type: The location of the flange in relation to the O.D. of the filter is sometimes offset to one edge of the filter for more clearance in an application.

Final Thoughts

No matter what kind, type, or brand of filter you choose, the important thing to remember is to check your filter regularly and replace or clean it as needed; your motorcycle, quad or side-by-side will thank you for it.