Maintaining optimum, unrestricted flow becomes a problem when the air must pass through a filter element. Conventional paper elements are very resistant to air flow because the filter material or medium is very dense. The greater the restriction the greater the power loss.

K&N engineers have made vast improvements in performance, durability and serviceability by directly addressing these inherent compromises. In the early '60s, K&N developed an oil impregnated cotton air filter gauze which exceeds the minimum filtration standards while offering little restriction to air flow. As a result, the first K&N filter element was manufactured by sandwiching several layers of surgical gauze between two sheets of wire mesh. The medium was then pleated to reduce the filter's overall size and to increase its surface area. Finally the cotton gauze was oiled to enhance it's filtering capabilities. The original concept exists today and remains the basic component used in all of our automotive, industrial, marine and motorcycle air filters.

K&N's oil-impregnated, cotton-gauze element is the basis of our filter, as well as K&N's overall dominance of the reusable air filter market. The process is expensive but well worth the effort. To further make the point, consider that square inch per square inch, our filter will flow an average of 50 percent more air compared to the average paper filter without sacrificing filtration efficiency.

By comparison, paper filters are made from compressed fibers. The spaces between these fibers provide microscopic holes the air must pass through. One by one, these holes become plugged with dirt and dust particles. Once a hole becomes plugged, the air must find an alternate route through the medium. As the filter collects more dirt, its resistance to air flow increases because there are fewer and fewer holes left open and as restriction goes up, horsepower and fuel economy go down. But to meet minimum filtration standards, the paper must be thick and/or the fibers must be tightly compressed and dense. Therefore paper elements that provide adequate filtration are restrictive to air flow by design. Any paper element that could flow as much air as an equivalent K&N would not provide safe filtration. Additionally, as a paper filter becomes more and more clogged, the pressure inside the filter drops while the atmospheric air pressure (approximately 14.6 psig at sea level) outside the filter remains the same. It's like using your lungs to draw the air out of a plastic milk bottle. When the pressure differential becomes too great, the bottle will collapse. The same thing could happen to your paper filter, although it is unlikely. But what will happen could be just as severe. An excessively high pressure differential created by a restricted filter can literally pull dirt particles through the paper medium. In other words, the performance of a paper filter, i.e. air flow through the filter and its ability to protect your engine, DECREASES near the end of its service interval.

The K&N air filter is somewhat more complex. The unique design features an oiled cotton fabric which holds airborne dirt particles. These dirt particles cling to the outside of the filter and actually become part of the filtering media. The cotton fabric is sandwiched between pleated aluminum screen. Pleating increases surface area which in turn promotes air flow and prolongs service intervals. Pleating exposes five times the surface area compared to a flat element like foam. The dirt particles collected on the surface of a K&N element have very little effect on air flow because there are no small holes to clog. Particles are stopped by crisscrossed cotton fibers and held in suspension by the oil. As the filter begins to collect debris, an additional form of filter action begins to take place because air must first pass through the dirt particles trapped on the surface. That means the filtration efficiency of a K&N element actually increase as the filter collects dirt. Tests have shown a K&N E-1500 filter will flow 60 percent of its maximum flow capacity after 50,000 miles of street use. And, considering a new K&N flows half again as much air as a comparable paper element, that same filter will provide all of the air the engine needs even after 50,000 miles. Conversely, dirt trapped by a paper element will impregnate the fibers which will impede air flow at a proportional rate. In other words, performance decreases dramatically as a paper element gets dirty. At the service interval, say 14,000 miles, air flow through a paper element can decrease as much as 70 percent. The efficiency of K&N's oiled cotton gauze medium has been proven time and time again. The condition of the filter can be monitored with a vacuum gauge. The vacuum reading increases as the filter nears its service interval. A high vacuum reading means the filter is dirty and needs to be serviced. Some trucks have logged over 100,000 miles with no loss in air flow as reported by the service technicians. Again this is due in part because a clean K&N filter will flow half again as much air as a comparable paper element. A K&N will provide superior filtration without sacrificing air flow for a longer period of time - that's performance with value.