Open cell industrial grade filter foam represents the latest advance in air filtration technology. An optimum air filtering system is very inexpensive insurance against untimely replacement of rings, valves, bearings, and fouled spark plugs. These items represent very significant maintenance costs. Higher performance, better gas mileage, and lower emission products provide additional benefits.
An air filter’s job is to keep dirt, dust, water and other particles from getting into your engine while allowing air to flow freely. Currently, there are three types of air filters available for your vehicle: paper, cotton/gauze, or foam. While paper and cotton/gauze offer the minimal standard for filtration, foam filters offer superior filtration and overall airflow.
Paper Filtration
Pleated paper elements are used by more vehicles than any other type because
they are the least expensive for the manufacturer to install as original
equipment from the factory. Since they are "throw away" items (cannot be
cleaned for reuse), they represent a large and profitable part of the
replacement market, while occupying our landfills.
Paper filters are a stacked matting of fibers creating a random weave approximately 1/2mm thick, and rely on the "screening" effect to stop dirt particles. Airflow per square inch is so poor that the paper must be pleated using many feet of material to make a filter. All dirt or dust particles must be caught on the surface or not at all. Each time a particle is caught, it plugs up a hole.
From the moment you start your engine, you have a rapidly decreasing airflow rate. Paper also has two other big drawbacks. Any moisture reaching the element causes the fibers to swell, reducing airflow even more. Another is the possibility of rupture. Paper is not a very strong material, especially where it is creased to form each pleat. Intake manifold backfires, or cleaning attempts with compressed air, usually rupture the paper leaving the filter ineffective.
Pleated Gauze or Fabric Filtration
This is another screen type that is only 2mm thick. If the dirt is not stopped on the surface, it is not stopped at all. These filters are sold on the pretense that they maintain an oil curtain for the air to pass through, thereby catching all dirt particles. It is impossible to maintain an oil curtain. The oil soaks the threads of the gauze or cloth, but does not span the openings; otherwise, the air could not get through. The dirt particles that do hit the threads have a good chance of being caught; the others simply go through. The reason the filter does not look dirty on the inside is because the dirt went into the engine. You can easily demonstrate this fact yourself by coating the inside of your housing or throttle body with a thin layer of grease to trap some of the dirt not caught by the filter or you can place a foam filter inside the gauze element to prove the same thing.
The one advantage that this type of element has over paper is greatly reduced airflow restriction; however, poor filtration efficiency is the price you pay. When dirt builds up, filtering action improves, but now the airflow is poor like paper elements.
Foam filters are made of tiny interlocking cells that trap and hold dirt particles throughout the entire volume of the foam (full depth filter). The cell strands stop the dirt while oil holds it until the filter is cleaned. The foam filter combines great airflow capability, huge dirt holding capacity and very high filtration efficiency.
Gauze filters feature multiple layers of oiled cotton fabric that captures the airborne dirt particles on the surface of the filter. Cotton fabric is sandwiched between pleated aluminum screens that increase the surface area. This provides additional airflow and prolongs service intervals. Gauze filters provide maximum airflow while trapping most dirt particles.
The development of this special foam represented a major advancement in air filtration technology. Foam air filters now combine great airflow capability, huge dust holding capacity, and very high filtration efficiency for extremely small particles.
Fully reticulated (open pore) foam is a honeycomb of tiny, interlocking cells of uniform size that create an impossible journey for dirt particles since there are no straight-through passageways. Each passageway (16 to 25mm long) is like hundreds of very small centrifugal/oil bath filters connected one to another. In this way, foam traps and holds the particles throughout the entire volume of foam. This is why they are referred to as "full depth" filters in contrast to the paper or gauze elements, which are screens, or "surface type" filters. The cell strands stop the dirt, while the oil film holds the dirt like fly paper until removed for cleaning.
Because foam is a full depth filter even as dirt is being stopped airflow can continue at a high rate by simply going around the stopped dirt. Unlike paper and gauze filters foam filters will not significantly decrease airflow as it gets dirty, giving you great airflow between cleanings.
True Flow foam filters are easy to wash and re-use. Follow the simple cleaning instruction included in your filter box at the cleaning intervals and enjoy great filtration and airflow for the life of your vehicle.
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The most damaging particle size ingested into an engine is 5-10 microns
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90% of ambient particle size on an average street is 10 microns or smaller
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90% of dirt passed through paper or gauze is done in the first 2.5% of the
filter's life
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A new paper or gauze filter does not effectively filter particles smaller
than 10 microns
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10% of dirt passing into an intake is retained in the engine
4/1/03