K&N Air Filters

K&N are famous for their air-filters. Marketed as 'filter-chargers', K&N primary design objective is enhanced air-flow which will directly lead to increased engine power. The primary function of an air-filter is to clean the air before it enters the engine. Because an engine's power output is proportional to the volume of air ingested at any given rpm (assuming the fuel management system can maintain a proper air-fuel mixture ratio), any restriction in the air-intake system will lead to a drop in engine power output. This generally holds true but lately TOVA has also learned that the length of the air-intake system, ie the air-intake pipe, can also influence power output. This means the whole air-intake system is an integral part of the engine design and should not be drastically changed if the power output characteristic of the engine is to be maintained. Maintaining optimum unrestricted air-flow becomes a problem when the air must pass through a filter element and K&N filter-chargers are design to directly address this issue.

The technical information about K&N air-filters in this article are derived from the K&N Automotive Air-Filters & Accessories catalog given to TOVA by the K&N representative for Malaysia SPEEDWORKS. TOVA is grateful to SpeedWorks owner Mr Toh Soon Hin for his permission to quote directly from the catalog for this article. As with the normal practice, all of TOVA's comments will be in red italic font. Publishing of this article does not represent TOVA's official position on any K&N products and we wish to highlight to readers again that TOVA's opinion is the you the reader is still the best judge of an aftermarket products suitability and effectiveness to your own requirements.

Paper VS K&N air-filter elements

Paper air-filters are made from compressed fibers. The spaces between these fibers provide microscopic holes through which the air passes while trapping the larger dirt particles. From usage, these holes will gradually become plugged with dirt and dust particles. Once a hole becomes plugged, air must find an alternate route through the paper medium. Thus for an efficient paper air-filter in use, as it collects more and more dirt, its restriction to air-flow becomes greater because fewer and fewer holes are left open for air passage. This will directly lead to power and fuel economy degradation.

To meet minimum filtration standards, the paper filter element must be thick and/or the fibers tightly compressed and dense. This means that paper elements that provide adequate filtration are also restrictive to air-flow by design. K&N also highlighted a potential effect for very clogged paper filters whereby too great a difference in air pressure between the atmosphere and inside the filter can potentially cause dirt to be pulled through the paper element (though K&N acknowledges that this is highly unlikely to happen). Thus, K&N feels that the performance of paper filters, ie air-flow through the filter and its ability to provide proper filtration to protect the engine, will actually decrease near the end of its service interval.

The construction of K&N filter elements are somewhat more complex. The unique design feature of K&N filters features an oiled cotton fabric which holds airborne dirt particles. Trapped dirt particles cling to the outside of the filter and actually becomes part of the filtering media. They have very little effect on air-flow because there are no small holes to clog. Instead the dirt particles are stopped by crisscrossed cotton fibres and held in suspension by the oil. K&N says as the filter begins to collect debris, an additional form of filtration begins to take place because air must now pass through the dirt particles trapped on the surface first. This means the filtration efficiency of a K&N element actually increases as the filter collects dirt.

Another design feature K&N highlights is pleating. The cotton fabric is sandwiched between pleated aluminum screens. This pleating increases surface area which in turn promotes air-flow and prolongs service intervals. K&N says pleating exposes up to five times the surface area for filtration compared to a flat filter element like foam. However, bear in mind that the stock paper filter in Hondas are also pleated. The aluminum screens are also claimed to straighten the air-flow, ie smoothen turbulent air that passes through the K&N element. The structure and benefits of the K&N filtering element is illustrated in the diagram above.

Strengths of the K&N filter

K&N says that square inch per square inch, their filter will flow an average of 50 percent more air than the average paper filter without sacrificing filtration efficiency. In addition, tests have shown that a K&N E-1500 filter will still flow 60 percent of its maximum flow capacity after 50,000 miles (or 80,000 km) or street use. This means even after 80,000km of use, a K&N filter will still flow 90 percent of the air-flow of a brand new paper filter. Paper filters by comparison may experience as high as a 70 percent drop in air-flow at their typical service interval of 14,000 miles (around 22,000 km).

Another famous attribute of K&N filters are their ability to be cleaned and re-used. To do this, simply wash, dry and re-oil the element at the prescribed intervals as illustrated in the cleaning instructions that comes with the K&N filter. K&N says their filters can be washed and cleaned up to 25 times. The recommendation is to inspect the filter every 30,000 miles (48,000 km) or 12 months. If cleaning isn't warranted, the element can simply be re-oiled by applying a small amount of oil to the clean side of the element to insure optimum filtration efficiency. Note most K&N filters or Filterchargers as they are called are warranted for 1,000,000 miles or 1,600,000 kms, ie more mileage than the lifetime of a typical car.)

Copyright Temple of VTEC
May 1999.