How They Work

Currently the industry standard medium for airmotive air cleaners is either oil impregnated foam (al la Brackett) or pleated paper-which is the most common. Both work but both are far from ideal when it comes to offering a low restrictive approach to allowing the engine (which is actually an air pump) to breathe. The problem with pleated paper is that often they tend to become clogged and thus greatly reduce the airflow to the point of bits of paper are ingested or sucked into the intake system thus creating a hole for gritty contaminants to enter the engine.

Independent Lab Test Results
In order to verify our filters maintain filtration levels necessary to protect your engine, K&N has test their filtering media through independent laboratories. The testing procedure used is the SAE J726 air filter test procedure established by the Society of Automotive Engineers (These are the folks who are supposed to know everything).
We have included a detailed example of test results using the SAE J726 procedure. These results you see below are for two individual air filters that each demonstrated among the highest overall filtration level we have achieved with our media

K&N is well respected in the high performance automotive markets for producing as producing a highly effective, but extremely low restrictive, washable (re-useable) pleated surgical cotton gauze filter which uses oil to help trap dirt and grit. Their oil impregnated cotton filters are well-proven known the world over as measurably increasing horsepower output as verified by dynamometer tests in nearly every installation from motorcycles to NASCAR winners. These filters can be washed, “re-charged” with fresh oil (included in the optional air filter re-charge kit), and re-used some 25+/- times and typically are thought to last the life of the engine. At an average of $100 to175+/-, they are understandably higher initially when compared to the typical dry paper filters initially, but overall they are more economical than paper elements as they are designed to last 10+ years and provide lower fuel flows as a bonus.

Air Filtration 101
Most people believe that all air filters function on a go/no go basis where dirt particles that are larger than the openings in the filter media are trapped while particles that are smaller than the openings can pass right through. A dry paper air filter does function in this manner. That’s why paper filters are so restrictive to air flow. The openings in this type of filter have to be very small to filter efficiently.
The oiled cotton media used in the K&N air filter functions in an entirely different manner. There are scientific principles that determine how an air filter removes dirt particles from the air stream. The first of these principles is known as interception, which applies to dirt particles traveling with the air stream. Air flow will always take the shortest path and as the air is forced to flow around the filter’s fibers some of the particles will contact the sides of the fibers and be captured. These particles are then held in place by the oil or tacking agent in the fiber.
Another principle is known as impaction, which mostly affects larger or heavier dirt particles. Impaction occurs when the inertia or momentum of the particle causes it to deviate from the flow path. In other words the heavy particles do not follow the air stream around the filter’s fibers but instead they run straight into the fibers and are captured.
The most important principle for our use is diffusion, which deals with the laws of physics that govern the motion of very small dirt particles. Small particles are highly affected by the forces in the air stream. Forces such as velocity changes, pressure changes, turbulence caused by other particles and interaction with the air molecules cause these very small particles to become random and chaotic. As a result, these particles do not follow the air stream and their erratic motion causes them to collide with the filter’s fibers. This phenomenon enables an air filter to capture dirt particles that are much smaller than the openings in the media. In addition, the way that dirt collects or loads on the K&N filter is very different. A paper filter exhibits "surface loading" which means dust collects only on the surface of the media. In contrast, K&N filters exhibit "depth loading". The multiple layers of cotton fibers provide many levels of dust retention. This characteristic allows the K&N filter to hold significantly more dirt per square inch of media than the average paper filter. Utilizing these scientific principles, K&N has been able to design an air filter that is very free flowing while also being highly efficient at removing dirt from the air.

Sometimes The Best Proof Is In The (Real World) Pudding

Most engine savvy GA insiders all know the name Terry Capehart as being the father of high performance blueprinting, balancing, and flow-balanced engine technology as it was introduced to both Lycoming and TCM aircraft engines. While this "port and polish" technology has long been used in high performance automotive engines for years, it wasn't introduced in GA engines until Terry founded Mena, Arkansa based High Performance Aircraft Engines some 20+/- years ago.
Using a Superflow computerized dyno to test various performance enhancement procedures on aircraft engines, Terry also knows the gains that can be had by providing a less restrictive intake and exhaust system. He has tested K&N air filters vs both Brackett and OEM paper elements and swears by them as he has seen the type of gains we talk about here. But more to the point, he has them on nearly every piece of motorized equipment he owns including his Harley.
In fact, he remarks that nearly every Harley dealer nowadays has a motorcycle dyno as nearly every Harley enthusiast wants to know exactly how much horsepower his two-wheeled pride and joy is putting out. As K&Ns are nearly a "must have" for most Harley guys, he recently had the opportunity to test his personal Harley "before" and "after" installing a K&N in place of the stock paper element and reports that it increased the HP of his 85+/- hp motorcycle approx. 3hp. When you transpose 3hp vs 80-85hp you about get the same percentage of increase that we are talking about here in Mooney or most GA engines...Imagine that! He verifies our findings and reports users who compare K&Ns vs Brackett filters should see more as the Brackett filter is more restrictive.

Tests done by Challenger Aviation (at approx. 240 cfm) show K&N filters typically flow 6.03 cfm as compared to 4.95 for the average pleated paper element and some 4.93 for oil coated foam (Brackett) variety. These figures alone verify K&N claim’s of increasing the effective horsepower of the typical Mooney of 3-5%+. These results were confirmed as being accurate representation of the applications by well-known aviation engine gurus such as Charlie Melot of Zephyr Aircraft Engines and High Performance Aircraft Engine's founder, Terry Capeheart. Interestingly both men have used K&Ns on their own vehicles for years and pay the same price for them as you.

How They Work

K&N’s Low Restrictive Cotton Gauze Elements