Kn Faq

1.How will a K&N filter affect my vehicle's fuel economy?

There is a relationship between air filter restriction and mileage. The theory behind this is simple, the harder an engine has to work to suck air through the intake tubes and air filter, the more gas gets wasted in the process. Many K&N users report an increase in their fuel economy after beginning to use our air filters. However, these experiences do not mean you will also experience a change in your mileage. We certainly understand why it is theoretically possible for a consumer to experience a mileage increase after installing a K&N air filter or intake system, however, we do not go so far as to make a general claim that our air filters and intake systems will provide an increase in mileage.

It is virtually impossible to make sweeping and general claims about mileage. Even the EPA fuel rating numbers for new cars are often not representative of the mileage you actually experience. There are many variables that affect mileage such as: tire inflation, the type of fuel, weather, elevation, the speed at which you drive, the gear in which you drive, the speed with which you accelerate, engine maintenance, excessive idling, cruise control, the grade of motor oil you use, and of course, the condition of your air filter. In short, mileage is complicated.

K&N filters are less restrictive than disposable paper or synthetic air filters and K&N Intake Systems are less restrictive than the factory installed air path. So K&N filter technology could be an important tool, when combined with other elements, to help keep mileage as high as possible.

Oh yeah, there's one more limitation imposed by science. If you take advantage of added power by driving more aggressively, you will reduce mileage. You cannot have your cake and eat it too.

2. What increase in horsepower should I expect from a K&N replacement filter?

K&N direct replacement filters which install into your vehicle's factory air box can provide an increase of between 1 and 4 horsepower. Results will vary depending on your vehicle, driving habits, load on the engine (towing for example), existing air system restriction, and other factors.

3. What increase in horsepower should I expect from a K&N air intake system?

K&N makes several different types and configurations of performance air intake systems. Depending on the year, make, and model of your vehicle, only one style of intake system may be available for that vehicle. All of our intake systems are dyno-tested and guaranteed to increase your vehicle's horsepower.

4. How often do I need to clean my K&N air filter?

If you have not experienced a decrease in mileage or engine performance, chances are your filter is fine and does not yet need cleaning. To be more specific, the filter does not require cleaning if you can still see the wire screen on the entire air filter regardless of how dirty it may appear. When the screen is no longer visible some place on the filter, it is time to clean it. When used in normal paved road, street or highway conditions, our replacement air filters that fit in the factory air box should require cleaning every 50,000 miles and our large conical filters on an intake system should require cleaning every 100,000 miles. When used in dusty or off-road environments, our filters will require cleaning more often. We recommend that you visually inspect your filter once every 25,000 miles to determine if the screen is still visible.

5. How can I tell the size of the engine in my vehicle?

North America: Most vehicles have an emissions decal placed either on the backside of the hood, on the radiator core support, or on the air box (the box that holds the air filter in place). Your engine size should be shown on the decal (4.0L for example). If you can't find the emissions decal you may also find the engine size printed on the decal under the hood that shows your engine's belt routing. You may also write down your Vehicle Identification Number that is stamped visibly near your driver's side dashboard top and listed on your vehicle registration certificate. This number can then be entered on K&N's part search by VIN webpage to find engine size as well as products for your vehicle. You may also contact your local dealership.

Europe: Your registration documents detail your engine size and type of vehicle. However, if you do not know whether your vehicle is spi (single point injection) or mpi (multi point injection) we suggest you consult your local dealer.

6. Can a K&N filter give my engine too much air flow?

No. An engine can only draw in a certain volume of air depending on the engine's size (measured by such things as bore, stroke and number of cylinders). Vehicles are designed to accommodate large changes in air pressure so they can operate at sea level or at an altitude of 14,000 feet. Engine computers adjust the amount of fuel required as a result of changes in air pressure (density). Air filter restriction when the filter is new and especially as the filter loads with dust will result in lower air pressure and availability similar to being at a high elevation. High-flow air filters that were invented by K&N were designed to reduce the work necessary to pull air through the filter and to increase air pressure. Increased air pressure is one of the key elements in producing more power.

7. Will using a K&N direct replacement filter void my factory warranty?

It is against federal law in the United States for a manufacturer to require the use of a specific brand of air or oil filter unless it provides a replacement air or oil filter, free of charge, under the terms of the vehicle warranty. For a more thorough discussion of this law known as the Magnuson-Moss Warranty Act, see our Vehicle Warranty.

8. Will installing a K&N performance intake system void my factory warranty?

Most K&N air intake systems are warranted for 1,000,000 miles which exceeds the warranty offered on the original factory intake system.

The installation of an air intake system should not void your factory warranty. It is never a bad idea to contact your local dealership and ask them before purchasing the new K&N system whether they will object. If they tell you an air intake system will void your vehicle warranty, please contact us and we will speak with the dealership directly to clear up the misunderstanding. Another idea would be to contact a different dealer who may have a different policy since many dealership actually sell K&N intake systems.

9. Do K&N air filters come pre-oiled or must they be oiled before using?

Almost all K&N air filters come pre-oiled and ready to use. The filter oil we use is red. A new oiled filter will appear red-pink in color. Some crankcase vent air filters come unoiled, however, they come with a small packet of K&N filter oil so they can be oiled before use. There are also a limited number of filters with specialty uses which are not pre-oiled. These items will be clearly marked as unoiled. Using an unoiled K&N filter will greatly reduce the filter's efficiency and void our product warranty on filters that come pre-oiled from the factory. If you receive a filter that is packaged in its cellophane wrapper and is unoiled, contact our Customer Support department at (800) 505-3274.

10. My filter came with a tube of sealing grease. How important is it?

It is rather important. It helps to maintain a seal on an uneven air box surface. If sealing grease is unavailable, white lithium or synthetic grease will work just fine. Petroleum-based products are not recommended.

11. Are K&N filters emissions legal?

All K&N direct replacement filters are emissions legal. They perform the same function as other types of disposable filters and fit right into the factory air box. K&N's custom, universal or conical air filters are not legal for street use in California or other states that have emission control standards. However, if the intake system you are attaching a K&N cone filter to is CARB exempt, the K&N cone filter will not change that status and will be part of the exempt system. Check your local laws if you are unsure what modifications may be allowed on your vehicle.

12. Are K&N performance air intake systems emissions legal in the US?

All intake systems are legal in most states because most states do not have regulations governing them. So this question really has to do with California and other states that have emission control standards. In order for an intake system to be legal in these states, it must receive an Exemption in the form of an EO number from the California Air Resources Board (CARB). To further complicate matters CARB exemption is issued only for specific part numbers used on specific vehicles. That means a part number can be CARB exempt for some vehicle applications and not others. There is no such thing as CARB Pending. A particular part number on a particular vehicle is either exempt or not. The best way for you to determine the status of the part number you are interested in for your vehicle is to look up the intake systems available for your vehicle in our vehicle/part search engine and check for CARB exemption. If you are unsure whether CARB exemption is required for a part to be legal in your state, check with your local or state motor vehicle or emissions agency.

13. How do I clean a K&N air filter?

Use a K&N Filter Care Service Kit, available at all major auto parts stores and a low pressure nozzle-free garden hose. A filter cleaned with K&N cleaning products will ensure a lifetime of performance from your air filter. Instructions for cleaning your K&N air filter are on our Air Filter Cleaning Instructions page.

14. How much oil should I use to re-oil my filter after it is cleaned?

The best way to ensure proper oiling is to use our squeeze bottle Recharger® kit. With a squeeze bottle, you simply run a bead along the top of each pleat on both sides of the filter. If using an aerosol Recharger® kit, make one light pass over the entire filter area front and back. The oil will then be evenly absorbed throughout the rest of the cotton medium over the next several minutes. We recommend you let your filter set for 1 hour to let any excess oil run off the filter. In any event, you do not need to worry about over oiling your filter and you should make sure the oil appears fully absorbed before re-installation.

15. Can I use anything other than K&N cleaner and oil?

For best results, we recommend that you use K&N air filter oil and K&N air filter cleaner. K&N air filter oil is a special compound which forms a very efficient tacking agent that helps capture dust. Our cleaner is a non-detergent degreaser. Petroleum products such as transmission fluid and motor oil will soften and destroy the rubber sealing edges. Harsh solvents and gasoline will harden the rubber seals causing the filter to distort (shrink). A mild detergent can be used in a pinch, but care should be taken to fully rinse it out. Rinsing detergent out of a filter is similar to getting soap out of a sponge; it's not that easy to do. Always make sure the filter is dry before re-oiling.

16. Can I use compressed air to dry the filter faster?

No, this can blow the filter material right out of the wire mesh and ruin the filter. Pick a nice day to clean the filter and let it dry naturally. A low pressure air flow such as from an industrial drying machine or blow dryer will help the filter dry more quickly.

17. Should I brush the wire screen with a toothbrush to get all the "crud" off?

No, this could tear up the cotton gauze.

18. 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:

Particle Size in Micrometers (Microns) Percent by Volume (+/- 3%) Particle Size in Micrometers (Microns) Percent by Volume (+/- 3%)
001 - 005 10.5% 01 - 05 36.0%
005 - 010 11.5% 05 - 10 18.0%
010 - 020 14.0% 10 - 20 20.0%
020 - 040 25.0% 20 - 40 17.0%
040 - 120 37.0% 40 - 120 09.0%
120 - 180 02.0%

As has become customary in the automotive industry, we use Coarse Test Dust for gasoline engine air filters and Fine Test Dust for diesel engine air filters. This practice of using different grades of test dust developed because Diesel engines require higher levels of filtration because they operate at much higher compression and require tighter tolerances than Gasoline engines.

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.

19. 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.

20. 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).

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.

21. More airflow means you are letting more dirt through, right?

No.  Filtration testing measures the percentage of dust retained before the filter reaches a terminal test pressure, often 10" of restriction above initial restriction. We use airflow as a simplified term to explain a more complicated physical process. The more precise description is restriction: K&N air filters create less restriction which helps an engine run better. An engine will only use the air it needs and our air filters do not result in an engine using more air than necessary. Rather, they result in the engine experiencing less restriction. The terms airflow and restriction are inversely related. Our air filters provide either less restriction at a fixed airflow rate; or more airflow as a fixed level of restriction. In neither case is more air being used than necessary.

22. Should I install the largest K&N filter that will fit in my race vehicle?

If an existing K&N filter is large enough to provide negligible restriction, a larger than required filter will not affect the amount of air an engine can take in, however, it will lengthen the filter's service interval. A longer service interval can be an important factor when racing in dusty, dirty environments.

23. Will a K&N filter cause my vehicle's mass air sensor to fail?

No, it is both impossible and ridiculous.

It is impossible because we know that the oil treatment on our cotton is very small (usually less than 2 ounces). Once the oil is properly and evenly absorbed through the cotton, no oil will come off, even under extreme engine conditions. It is ridiculous, because no dealership or service provider has ever been able to provide us with evidence to support this "myth," and in fact, our investigations have revealed that even authorized dealerships are simply speculating and do not have the test equipment necessary to know whether the sensor has failed or why. It is even more ridiculous because some car manufacturers use and sell air filters treated with oil on a regular basis. There are also major brands of disposable air filters that are treated with oil. We all use oil for the same reason, it helps in the filtration efficiency of an air filter.

Out of the millions of air filters we sell, we only receive a handful of consumer complaints each month that a dealership or service provider has blamed a vehicle sensor repair on our product. We take each complaint very seriously and see it as an opportunity to stop a consumer from being taken advantage of.

As a result of our standing up for consumer rights and providing assistance to resolve a disagreement, we have had over 100 actual sensors sent to us by dealerships who claimed our product had caused them to fail. Microscopic, electronic and chemical testing revealed that none of the sensors were contaminated by K&N oil. What is perhaps the single biggest clue to what is going on is that over 50% of these sensors were not broken in the first place for any reason.

Facts You Should Know About Air Filters

We believe the primary function of an air filter is to deliver both high airflow and superior dirt protection.We design our air filters to provide minimum restriction allowing high airflow into an engine. In the vast majority of cases increased airflow will increase engine performance measured by horsepower and throttle response (torque).The performance benefits of maximum airflow are clear, compelling and well documented. That is why so many professional racers are willing to run expensive vehicles with no air filter, as opposed to installing a disposable air filter. They are seeking the additional horsepower and throttle response needed to win the race.

We design our air filters to provide superior filtration of the contaminants that can harm your engine while maximizing the airflow characteristics of the filter in question. The ability of an air filter to protect your engine is generally measured in accordance with testing procedure ISO 5011. We subject a sample of our filter designs to this test procedure using Coarse Test Dust, which includes particles ranging in size from less than 5.5 microns to 176 microns. As a point of reference, a human hair is approximately 50 microns in diameter. The result of the above test procedure is a specific air filtration efficiency number. This efficiency number represents the percentage of test dust retained by the filter and thereby kept out of an engine. Our goal is to design our air filters to achieve maximum airflow while targeting overall filtration efficiency at 98%.

Because no two air filters are alike, the specific airflow and overall filtration efficiency will vary depending on the filter in question. However, you can rest assured that each air filter we sell, has been designed to achieve high air flow while providing superior filtration.

Both air flow and dirt protection are critical to engine performance. For this reason a consumer should always evaluate an air filter based on both its filtration efficiency and air flow capabilities. It is very easy to design an air filter that exhibits high airflow simply by reducing its filtration to unacceptable levels. As the "look" of a K&N air filter has become popular, many companies have begun offering products that copy that "look". While imitation is said to be the sincerest form of flattery, our own testing has shown that many of these look-alike products do not provide a safe level of engine protection.

What's the Big Deal About Air Flow?

Simply put, Everything! At its most basic level, an engine is an air pump. More air entering the engine increases the efficiency of the combustion process creating more horsepower and torque. Horsepower is a measure of the engine's maximum power while torque measures how quickly you can accelerate.

The K&N Filtercharger® is designed to increase engine performance in both horsepower and throttle response by reducing air flow restriction.

Maintaining optimal, unrestricted air flow becomes a problem when it must pass through a filtering medium. The level of air resistance varies depending on the size, surface area and physical attributes of the filtering medium.


A Word About Filtration Requirements

There are few areas more confusing than identifying dirt retention requirements when it comes to air filters. Most vehicle owner's manuals remain silent on the point. In fact, few air filter manufacturers publish any information as to the filtration efficiency of their filters. This stands in marked contrast to oil and fuel filters where there is a relatively large amount of information regarding filtration requirements and capabilities. Studies have shown most engine wear is caused by particles 10 to 20 microns in size. K&N air filters, like most quality disposable air filters, provide excellent filtration of these particles.

To ensure our air filters provide a high level of dirt protection, we regularly test our air filter designs using the testing procedure described above. Those tests demonstrate K&N air filters generally achieve overall filtration efficiency in the range of 97% - 98%, while some of our air filter designs have achieved levels as high as 99%. The fact that our air filters at times reach overall filtration efficiencies as high as 99% while maintaining high airflow is a testament to the quality and capabilities of our oil impregnated cotton air filter medium.

On occasion we see "new" air filter media's developed and sold under the premise they provide increased levels of dirt filtration. More often than not, as opposed to quoting specific efficiency numbers, this "increased protection" is described as increased dirt retention capacity, meaning the filter can hold more dirt before requiring replacement. Remember, K&N air filters have always provided a service life in excess of disposable filters and then only require cleaning and oiling for re-use.

We encourage customers to do their homework and be aware of the filtration capabilities of an air filter before they buy. Our own testing has revealed wide differences in filtering capabilities. We were surprised to see some disposable paper air filters with an overall filtration efficiency as low as 93%. We hope we have provided enough information to ensure consumers know what they are getting when they buy a K&N air filter.

Filtration 101 - A Deeper Cut

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.

Independent Laboratory Test Results

In order to verify our filters maintain filtration levels necessary to protect your engine, we test our filtering media through independent laboratories. The testing procedure used in the past was the SAE J726 air filter test procedure established by the Society of Automotive Engineers, however this procedure was recently superseded by testing procedure ISO 5011.

We have included a detailed example of test results using the SAE J726 procedure. These results are for two individual air filters that each demonstrated among the highest overall filtration level we have achieved with our media.

Paper vs K&N

To meet minimum filtration standards, paper air filters must be thick and/or the fibers must be tightly compressed and dense. Therefore paper elements that provide adequate filtration are more restrictive to air flow by design. Additionally, as a paper filter becomes more and more clogged, the pressure inside the filter drops while the atmospheric air pressure (approximately 14.7 psia 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.

Disposable Paper Air Filter

Disposable Paper Air Filter

1. Pleated wood pulp bonded together.

2. As dirt builds, passages are plugged and filter must be replaced in approximately 10,000 miles.

3. Irregular passages filter out dirt on a go/no go basis.

4. As fibers swell from moisture or oil blow-by vacuum pressure increases and airflow decreases.

5. Turbulent filtered air.

Typical Foam Air Filter

Typical Foam Air Filter

1. Lack of surface area hinders air flow and dirt holding capacity. Open cell foam usually saturated with oil.

2. Dirt builds on outside and blocks the openings.

3. Higher vacuum pressures distort the cells drawing dirt deeper into the filter.

4. Airflow is reduced as cells become blocked.

5. Turbulent filtered air.

The K&N air filter is somewhat more complex. The unique design features multiple layers of oiled cotton fabric which captures the airborne dirt particles. These dirt particles cling to the fibers of the filter and actually become part of the filtering media. This process, known as depth loading, allows the K&N air filter to retain significantly more dirt per square inch than a paper filter. The cotton fabric is sandwiched between pleated aluminum screen. Pleating increases surface area which in turn prolongs service intervals. Pleating exposes substantially more surface area compared to a flat element like foam.

The dirt particles collected on the surface of a K&N element have little effect on air flow during much of its service life because there are no small holes to clog. Particles are stopped by layers of 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 a K&N air filter continues to exhibit high air flow throughout the life of the filter while it is accumulating dirt. At the same time, the air flow for an average paper air filter can decrease dramatically as the paper element gets dirty. So as dirt accumulates, the performance advantages of a K&N air filter can increase! Tests performed by an independent laboratory commonly known as the Frazier Permeability Test have shown that the Medium used in K&N air filters flows more than 300% more air than paper air filter medium when compared on a square inch per square inch basis. A Square inch comparison is not directly proportional to the increase you can expect from installing a K&N air filter in replacement of a paper air filter due to the effect of such things as filter size, number and depth of pleats. However, you can be assured a K&N air filter will provide dramatically more air flow which can enhance engine performance.

K&N vs. Disposable Filter Life

Filter Life

Stop Throwing Away Your Air Filter!
One K&N air filter will last the life of your vehicle. Assuming you drive your vehicle 150,000 miles and bought and installed a disposable filter every 15,000 miles, you would throw away 10 disposable air filters.

Washable and Reusable

All of our air filters are washable and reusable. They can be easily cleaned and oiled using our K&N Recharger kits as many times as reasonably necessary. In our testing laboratory, we have washed and re-oiled one K&N Air Filter more than 100 times and it still performed up to specification. We recommend you check your air filter every 30,000 miles, however, under most street conditions the filter will not require cleaning until 50,000 miles of continuous use. And yes, we've heard the stories of customers who ran their K&N filter for 100,000 miles without a cleaning, but we believe cleaning after 50,000 miles to be the most beneficial service life without sacrificing air flow.

Stock Replacement Filters

We manufacture stock replacement air filters to fit most vehicles on the road today. These filters are designed to replace the factory air filter that came with your car. They fit into the factory air box and are engineered to seal tightly with no air leakage. These filters are made with the same filter media used in our racing filters and put a little bit of performance into your every day driving experience. Our stock replacement filters are backed by our Million Mile Limited Warranty and are emissions legal in all 50 states.

Our stock replacement air filters are washable, reusable and can handle all driving conditions. Water will not damage their performance and with proper cleaning, they will last the life of your engine. And of course, they offer high air flow and that means performance!

Our replacement air filters are designed to provide up to a 4% increase in horsepower and torque. The amount of performance gain varies from vehicle to vehicle based on the overall factory air intake design. The greater the restriction created by the stock paper element, the greater the potential performance gain when you switch to a K&N.

The airflow comparison charts below are for two individual stock replacement air filters sold by K&N. The tests were performed in a dust-free environment on laboratory equipment. Flow comparison results will vary depending on part number, vehicle application and barometric air pressure. For a complete description of the air flow testing method used by K&N to develop the information in the charts below and other published air flow results.


Beyond the Stock Air Filter and Air Box

Addressing the next area of restriction, K&N engineers looked at the vehicle's air box (the container that houses the air filter) and any hoses or duct work connecting it to the engine. Because the air must first travel through this system before it reaches the carburetor or throttle body, the overall size and shape of the system has a profound effect on air flow. Air, like water, does not like to turn corners nor does it react favorably when confronted by an obstruction such as a sharp bend in a hose or a baffle. In many cases, the air box and/or the hoses and duct work used to create the air filtration system is just as restrictive as the original paper filter element. In some extreme cases, the air box and/or the air delivery system is the greatest source of restriction. The inlet to the air box is a good example. In many instances this opening is one half the cross sectional area of the throttle body or carburetor opening. It would be like trying to run a marathon while breathing through a soda straw.


An original-equipment cylindrical air cleaner box covering a throttle body or carburetor is another example. Most often, these round air cleaner housings are sealed to the outside air. The engine must then breathe through a snorkel attached to the perimeter of the housing. At times the snorkel is fed through a network of hoses and scoops.

To directly address the problem, we introduced a line of air intake kits, the most popular of which is our Fuel Injection Performance Kits (better know by the acronym, FIPK). These kits replace both the air box and the restriction. Our FIPKs vary in design because they are application specific meaning each kit is engineered to fit a particular make, model and year of vehicle. FIPKS utilize a 360-degree filter design which provides increased surface area to promote air flow.

Off-Road and Racing Off-Road

An air filter element becomes an insurance policy when used in off-road applications. Competitors will sacrifice a high-tech engine for a chance to win a race - but to win, they must finish. If the engine ingests too much dirt and debris, it may die an ugly death before the vehicle can cross the finish line.

You might think this would be the perfect application for an inexpensive, throw-away paper filter. But remember, in competition a little extra horsepower can mean the difference between coming in first or finishing second. The air filter now becomes an important part of the performance package.

K&N air filters are designed to provide minimum restriction long after disposable air filters have begun choking an engine. In other words, due to its characteristics, the restriction of a K&N replacement filter increases at a slower rate when compared to a disposable filter, i.e. a K&N filter will last longer under the same conditions. That's why most off-road competitors choose K&N filters.

In a hypothetical 24-hour off-road race to further the point, a properly sized K&N filter will see the racer through to the end with cfm to spare. The equivalent disposable air filter, on the other hand, will need to be replaced with a fresh element to ensure the engine has an adequate supply of air to complete the course. A K&N will provide excellent filtration without sacrificing air flow for a longer period of time - that's performance with value.


One might consider a paved road course or oval track as a clean air zone. After all, how much dirt and debris could be hovering above an asphalt track?

Subscribing to that theory, a road racer may elect to forgo an air filter in favor of large volumes of unrestricted air. However, testing the theory using an air filter enclosed in a vented housing should dispel the myth. The filter and housing will trap particles of loose trash kicked up by other race cars during the heat of battle. Dirt, small stones and pieces of shredded rubber expelled from soft compound racing tires can be found inside the housing after even a short race. Once a driver, car owner or engine builder realizes just how much trash is thrown around during a normal race, few would expose their expensive engines to unfiltered air in future events.

Whenever possible, performance enthusiasts should install a K&N 360 degree open-element filter. A correctly sized conical or round filter will deliver virtually unrestricted air flow. And, as we have learned, providing the engine with all of the air it needs promotes optimum performance. In a high speed application, a K&N filter will straighten the air which counteracts turbulence.

Straight cut velocity stacks, for example, pose a unique problem. Exposed to the outside air, velocity stacks experience a phenomena that actually hinders performance at high speed. We are referring to stacks and air horns that protrude through the hood and extend into the air stream so the direction of the air rushing over the car is at a perpendicular angle to the length of the tube.

Air moving rapidly over these stacks create turbulence inside the opening. At high speed, the rushing air tends to create a partial vacuum inside the tube. The condition is counterproductive to air flow. The phenomena also effects open carburetors. The higher the ground speed, the greater the problem. Vacuum created by the engine is trying to coax air into the cylinders and the high speed air flowing over the open end of the stack is causing resistance.

Reversion creates other problems. In an automotive application, reversion refers to reversed air flow, or in simpler terms, it's when air in the intake runner reverses direction for a split second. The condition is caused when a burst of pressure escapes into the intake runner from the cylinder during valve overlap.

Reversion creates resonance shock waves inside the tubes which exit the open end of the tube at various rates depending on engine speed. It has also been proven that these shock waves interfere with each other when the stacks are in close proximity.

Installing a free-flowing air filter on top of each stack or over the carburetor air horn eliminates these conditions. How? The solution is simply explained. The filter creates a plenum over the opening. Air entering the filter is slowed, smoothed and straightened. The filter then becomes an endless source of calm, clean air. Shock waves dissipate within the confines of the plenum without interfering with the shock waves emitted from an adjacent stack.

A Better Choice For The Environment

K&N cotton air filters have always been washable and reusable, designed for the life of an engine. If you assume an engine life of 150,000 miles in which a disposable air filter must be replaced every 15,000 miles, only one K&N air filter would be used during the same period in which 10 disposable air filters were discarded. Considering there are millions of vehicles throughout the world, the volume of disposable air filters that could be eliminated from our landfills is a staggering number.

Filter Selection

Cartoon Figure

If maximum horsepower is the objective, the size and shape of the air filter element is paramount.

Let's first consider shape. When fitting a conventional round filter on top of the engine, such as a carburetor, central fuel injection or throttle body fuel injection, we have found a large diameter, short filter will flow more air than a small diameter, tall filter. For example, a 10-inch diameter filter 2-inches tall will flow more air than a 5-inch diameter filter that is 4-inches tall. Where space permits, the height of the filter should be between 1/5 and 1/4 of its diameter.

The shape of the filter is less important if the application calls for a remote mounted filter, which includes many late model fuel injected models. Typically these vehicles will use a flat panel filter or a conical or cylindrical shaped filter with a rubber mounting flange designed to be mounted on the end of the inlet hose.

That brings us to size.

Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting .75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area.

A=(CID X  RPM) / 20,839

A = effective filtering area
CID = cubic inch displacement
RPM = revolutions per minute at maximum power

Example: A 350 CID Chevy engine with a horsepower peak at 5,500 rpm.

A=(350 X  5500) / 20,839 = 92.4 square inches

If you are sizing a panel filter, multiply the width of the filter area (not the rubber seal) times its length. If you are sizing a round filter, use the following formula to determine the height of the filter.


A = effective filtering area
H = height
D = outside diameter of the filter
3.14 = pi
0.75 = the rubber end caps


H=(92.4 / 12 * 3.14)+0.75 = 3.20 inches

Referencing the K&N catalog shows the proper filter for this application would be an E-1500 which is 3.5 inches tall. Keep in mind, this is the minimum size requirement. To extend the service interval and to provide an even greater volume of air to the engine, install the largest filter that will fit in the space allotted. If the space above the engine is restrictive, perhaps a remote filter arrangement could be used to gain space.

Off-road conditions require added filter area. A filter should be sized 1-1/2 to 2 times larger than normal for any conditions that could be considered severe. In this case, the E-1500 used in our example should be replaced by an E-1120 or an E-1150. For long distance off-road events, two double-size remote mounted filters would be best.

Some important tips about K&N Filterchargers

Service Interval

A K&N Filtercharger is a high-performance air filter, both in terms of air flow and filtration. However, the service interval can vary widely depending on the severity of the driving conditions. The service interval can be from 100 miles in a desert-racing environment to 50,000 miles for normal street use. The proper way to determine when an air filter needs service is with an air restriction gauge. Such a device is commonly used on heavy duty trucks and construction equipment. A restriction gauge, measures the pressure differential inside and outside the filter and gives the information in different forms of measurement. As the filter collects more and more dirt, the restriction value increases. At a predetermined point or rate of restriction, the filter is serviced. The maximum allowable restriction for a K&N Filtercharger is 15" of vacuum (water). If the restriction is allowed to go higher, the filter media might become so restricted that the element could distort allowing dirty air to bypass the filter and enter the engine. Conversely, cleaning a filter too often will shorten its serviceable life expectancy. Installing a restriction gauge will optimize service intervals and take the guess work out of your maintenance schedule.

Service Life

K&N air filters are washable and reusable. They are easily cleaned and oiled using a K&N Recharger kit. They can be cleaned and oiled as many times as reasonably necessary. In our testing laboratory, we have washed and re-oiled a K&N Air Filter more than 100 times and it still performed up to specification.

Limited Warranty

All K&N stock replacement air filters are backed by our famous million mile limited warranty. See our warranty page for stock replacement and off-road warranty details.


When servicing a K&N filter, take care not to over-oil the element. Besides impeding air flow, excess oil can migrate into the intake system where it can coat electronic sensors, which some OEM's claim may hinder the sensors' operation and result in a repair that will not be covered under warranty. Although K&N disagrees with such claims in order to avoid a dispute with an OEM over the denial of a warranty claim, we suggest that you be careful not to over-oil your K&N air filter. Never saturate the filter. If oil drips from the filter, wash it and start over. Use only K&N oil. For example, an E-1500 filter has 92.4-inches of surface area requiring 1.707 fluid ounces of oil.

Fit and Finish

Installed Filter

When installing a K&N filter, check all gaskets, clamps and seams for damage and/or deterioration. Check the filter's sealing surface. Do not install a filter if the seal shows signs of damage or deterioration. Check for cracks in the air box, particularly at the seams and around the corners. Such defects could cause air leakage around the filter. Also, check to insure the filter is sealing properly in the air box. A plastic air box can warp from age or continuous heat cycling. Apply a thin layer of filter grease on both sides of the seal each time the filter is installed. An impression in the grease will indicate a positive seal. Check any lines or hoses connected to the air box or adjoining hoses leading to the engine. Engine oil in the air box, resulting from excessive blow-by, will cause the filter to shrink and possibly lose its seal. Clean any dust or debris out of the air box with a damp cloth, making sure nothing enters the air inlet while the filter is out. Never start the engine without the filter in place. Use only K&N Air Filter Recharger® to clean your filter. Harsh household cleaners can damage the cotton material and/or the rubber seal. Check the outside of the medium for broken wires, rips or tears. Do not use an element that shows signs of damage or wear. Use K&N Air Filter Sealing Grease on the sealing surface that contacts the air box. Do not use sealing grease on clamp-on type filters. If a filter is especially difficult to install, it will come with an instruction sheet explaining the correct installation procedure. Keep the instruction sheet with the vehicle for reference anytime the filter is removed. It is very important the filter be installed correctly. The filter can be positioned in the base or the lid, whichever is more convenient and makes the installation easier. Do not use excessive force to install a filter.

Vehicle Warranty

Contrary to what you may have heard or read, in the USA, a K&N Filtercharger will not void your vehicle warranty. The Magnuson-Moss Warranty Act, passed in 1975, prohibits a manufacturer from conditioning its warranty of a consumer product upon the consumer using any article or service (other than one provided without charge under the warranty) which is identified by brand, trade or corporate name, unless expressly authorized by the Federal Trade Commission. If the manufacturer does not provide air filters free of charge, they cannot void the vehicle's warranty simply because you have installed an aftermarket air filter.


We offer thousands of stock replacement applications, hundreds of universal clamp-on filters and dozens of Fuel Injection Performance Kits. Our goal is to provide the highest quality component at a competitive price. A K&N Filtercharger will be the last filter you will ever buy for your car, truck, motorhome, motorcycle, ATV, boat or jet ski - Guaranteed.

Emission Warranties on New Vehicles

THE MYTH: A manufacturer's new-vehicle warranty is automatically voided once an aftermarket part (non-original equipment) is installed.

THE TRUTH: Rarely does the use of aftermarket parts violate a new-vehicle warranty.

THE RULES: Federal law, (the Clean Air Act), requires two emissions warranties: a "defect" warranty and a "performance" warranty.

"Defect" warranties require the vehicle manufacturer to produce a vehicle which, at time of sale, is free of defects that prevent it from meeting required emissions levels for its useful life, as defined in the law.

"Performance" warranties require that vehicle manufacturer make repairs - at no cost to the owner - should a vehicle fail to meet certain levels of emissions performance during the warranty period. This period ranges from 2 years (or 24,000 miles) to 5 years (or 50,000 miles) for most parts, and up to 8 years (or 80,000 miles) for certain emission-controlled parts, specifically, the catalytic converter, the electronics emission-control unit and the on-board diagnostic device (check owner's manual for specifics on your vehicle).

Consumers are protected under a parts self-certification program administered by the Environmental Protection Agency (EPA).

If a parts maker self-certifies it's parts under this program, the vehicle manufacturer cannot void the emissions warranty even if the certified part fails and/or is directly responsible for the emissions warranty claim. In this situation, the vehicle manufacturer must arrange a settlement with the parts manufacturer, but the new vehicle warranty is not voided under the law.

If a parts maker chooses not to self-certify it's parts, the only case where a vehicle manufacturer can void the emissions warranty is if a non-certified aftermarket part is proven to be responsible for an emissions claim.

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