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Air Filter Facts
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Home
| Search for Products
| Where to Buy | Facts
| Testimonials
| FAQ's
| News & Events | Contact K&N
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Air Filter Facts |
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| Disposable Paper Air Filter | |
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| Typical Foam Air Filter | |
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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.
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K&N vs. Disposable Filter Life |
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Stop Throwing Away Your
Air Filter! |
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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, see the section on this web site “K&N Air Flow Testing.”
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.
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.
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.
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| 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. |
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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.
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| A = effective filtering area H = height D = outside diameter of the filter 3.14 = pi 0.75 = the rubber end caps |
| Example: |
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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
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.
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, as explained in more detail on this web site, 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. Follow oiling instructions included with your filter or refer to the instructions listed here.
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 Cleaner 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.
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.
Letter from K&N Regarding Vehicle Warranty and K&N Replacement Filters
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.
Copyright © 2008 K&N Engineering, Inc. All Rights Reserved.
