I'm probably going to regret posting this, but I think it is a pretty honest answer from K&N on their filter performance in regards to removing debri. I have used K&N filters for years, mainly because during the summer where I live and wheel (Oregon,TSF) it is extremly dusty, and I would be replacing a filter every weekend, and also certain performance mods require a change from the stock air box. Anyways, here is K&N's answer for what its worth.
21. What is the micron rating and efficiency of a K&N air filter?
Air filters are not measured by micron size. As an industry standard, air filters are tested in accordance with the ISO 5011 test protocol to measure capacity (the physical amount of dust a filter can hold before cleaning is necessary) and efficiency (the filter's ability to trap and hold dust). See technical service bulletin 89-5R from the Filter Manufacturer's Council. The dust selected for the test contains a specified distribution of different particle sizes according to ISO standards. The content of the two most commonly used types of ISO test dust for air filters is as follows:
ISO COARSE TEST DUSTISO FINE TEST DUST
Particle Size in Micrometers (Microns)
Percent by Volume (+/- 3%)
Particle Size in Micrometers (Microns)
Percent by Volume (+/- 3%)
001 - 005
01 - 05
005 - 010
05 - 10
010 - 020
10 - 20
020 - 040
20 - 40
040 - 120
40 - 120
120 - 180
Our testing has demonstrated that on average, K&N replacement air filters and air intake systems have a cumulative or Full Life filtration efficiency of between 96 and 99%
. Different filters test at different efficiencies due to changes in their shape, surface area and relationship to the direction of air flow through the factory air box or test housing. Like most air filters available in the USA, our filters will provide all the engine protection you need.
For more information on our testing, see our K&N Product Testing
22. What are the air filtration requirements for my vehicle?
There is no published requirement for vehicle filtration. Car and truck owner's manuals are silent on the issue and you will find very few companies that even credibly discuss filtration efficiency. We believe this demonstrates that most air filters sold today provide adequate levels of filtration. Particularly when compared with the filtration provided by fuel and oil filters.
23. Some air filter companies tout their high filtration levels in the 99th percentile. Doesn't higher filtration mean a better air filter?
No. The quality of an air filter can only be judged by reviewing all four important characteristics. 1) Restriction while loading with dust; 2) Filtration efficiency as a percentage; 3) Dust holding capacity before the filter needs cleaning or replacement ; and 4) filter life. Any company designing an air filter must make choices about these four characteristics and how their filter will perform in each area. Generally speaking, each characteristic of an air filter has an inverse relationship to at least one of the others, meaning, as filtration efficiency goes up, restriction increases and capacity or service life decreases. So an air filter manufacturer can design an air filter to have ultra high filtration efficiency by compromising the filters restriction, capacity, and/or service life. We judge the quality of an air filter based upon the proper balance of these four essential criteria. Maximizing one at the expense of others sounds more like a marketing goal rather than an engineering goal. So the basic answer to the original question is that higher filtration is not necessarily a good thing when it comes at the expense of restriction, reusability and/or capacity. While the benefits of a filter with 99.9% filtration are unknown, the benefits of low restriction are measurable and clear. Low restriction helps an engine perform more efficiently generating more power and torque.
That would lead a reasonable person to ask what then is a safe level of filtration. This question is literally unanswered. Minimum air filter specifications are generally not called out in vehicle owners' manuals, nor will you find much published information on air filtration requirements from vehicle manufacturers. We have never seen a scientific study concluding what levels of filtration efficiency correspond to various levels of engine wear. Some large air filter companies do not even publish information on the efficiencies of the air filters they manufacture. It is K&N's opinion that both the Fine and Coarse Test Dust mixtures used in air filter testing contain such a high concentration of small particles that even filtration efficiency numbers as low as 90% may provide adequate engine protection. Remember that almost 11% of COARSE test dust is smaller than 5.5 microns (the size of a red blood cell). For a detailed explanation of our testing protocol, click here
The fact is that an engine is not a pristine environment. Fuel enters after passing through a fuel filter, combines with air which is ignited to explode in a pressurized chamber. The combustion is not 100% efficient and leaves residues behind that must be flushed from the engine. Engines have tolerances or measured gaps between surface areas. While there are few if any studies on engine wear, it would seem reasonable to speculate that particles less than 5.5 microns create little engine wear unless ingested at very high levels of concentration. As support for this theory, consider the filtration levels provided by fuel filters and oil filters that sometimes tout their ability to filter particles above 10 or 20 microns.
If you really want to compare two air filters, you need to know all four characteristics mentioned above. Consumers can then choose what matters most to them. But comparing two air filters with only one piece of information is like saying a bicycle is better than a car based solely on a comparison of mileage. Yes the mileage is better, but a car has a few other benefits (speed, comfort, keeps you dry in wet weather) that just may offset the mileage disadvantage.
We design air filters to provide low restriction throughout the filter's service interval. We seek the best balance between airflow and filtration recognizing they are inversely related. After nearly 40 years in business with millions of air filters sold, we have a track record you can trust and the experience that can only be earned through years of focusing on just one thing. But even our experience is not enough. We operate a fully staffed air filtration lab that operates on a year round basis with two test stands. The lab was designed by Southwest Research and is calibrated regularly to ensure our test results are reliable. This testing is an essential ingredient in verifying our air filters meet our own high standards of excellence. Making a great air filter is no accident and we are confident our air filters provide outstanding engine protection with huge air flow advantages throughout the air filter's service interval. That's why we back up our replacement air filters with both a Million Mile Warranty
and our Consumer Protection Pledge
K&N's air filtration lab tests air filters according to ISO5011 test protocol. The ISO (International Organization for Standardization) is an international organization which establishes standards used by different industries worldwide. The ISO does not establish any standards for an air filter's effectiveness; they establish standards for the testing procedures used to find air filters' capacities and efficiencies only under the fixed and chosen parameters of the test being conducted. In the case of engine air filters, the ISO5011 test ensures consistency in the procedure used to test a filter's initial restriction, initial efficiency, cumulative (full-life) efficiency, and dust holding capacity. Using a standardized test procedure and disclosing the user selected variables ensures the same test can be run anywhere around the world. Some of the requirements of the ISO5011 test procedure are that the temperature of the test lab must be maintained at 23 degrees Celsius +/- 5 degrees Celsius, and the relative humidity of the test lab must be maintained at 55% +/- 15%, for the entire duration of the test. During the test at each weighing stage (when the mass of the filter is found) the humidity can only vary +/- 2%. Also, all test dust which is fed into the air filter must be "found" after the test is completed. That means if 10 grams of test dust is fed to the filter during the test, but only 8 grams of dust is found trapped in the filter after the test, part of the ISO5011 test procedure requires that the remaining 2 grams of dust must be found. The dust could be in the air filter housing, the air duct, or the absolute filter which traps any dust that passes through the air filter, but wherever it is it must be accounted for. If any of the requirements of the ISO test procedure are not met, the test is not valid. A company's participation in testing using ISO5011 test procedures is strictly voluntary. Conducting an ISO5011 test requires a considerable investment in both time and equipment, and many air filter companies simply do not have the resources to complete an ISO test in-house. K&N views this test procedure as a valuable part of our research and development process.