Is it really worth putting a Cold Air Intake on 370z and what HP gains

Originally Posted by K&N Air Filters

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 96% - 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.

Independent Lab Flat Filter Test Results - Click Here!

Independent Lab Round Filter Test Results - Click Here!

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





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





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




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, 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.

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.

Racing

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

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 = 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.







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





Example:







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.

Over-oiling

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.

Fit and Finish

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.

Letter from K&N Regarding Vehicle Warranty and K&N Replacement Filters

Summary

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.

Originally Posted by Bob The Oil Guy

Air Filter Filtration Test



In the top left corner is the heavily advertised K&N. Going in standard English (not Arab) book order (left to right etc.), next is the Amsoil air filter. After that is the Napa Gold paper air filter. On the bottom row are the Jackson Racing filter, Racing Beat air filter, and the Fram air filter I removed from the box from the previous owner. That Fram had to rob airflow seeing all the metal in the backing. It has to be blocking 30% or more of the total area for airflow. The K&N is of course a steel cage with cotton gauge lining inside the cage which is oiled. I have used K&N air filters for years on various cars. I always heard they let in more dirt. It is actually the argument over flow and filtration on the internet that inspired this test. There are no definitive independent tests. Automotive enthusiasts have to rely on the claims of filter makers, which I feel are misleading. The Amsoil filter is a two stage foam air filter with a backing steel mesh. The first foam is coarse, and the upper foam below the cage is a very fine foam a lot like you see in HEPA filters. The initial foam is very coarse and definitely synthetic like a plastic. Think of the plastic scratch pads for pots and pans. The Jackson racing filter is almost identical in construction to the Amsoil expect it has a rubber gasket around the edges like the K&N and paper filters to fit the stock airbox. The Amsoil is oversized a small amount and just squeezes down into the airbox. The Racing Beat filter is really just one layer of very fine foam with a metal backing. The Napa filter is just their stock Napa Gold offering. It is some sort of paper and fiber combination with a metal frame down the middle and the rubber ring around it. Everyone says Fram air filters are not that good, but I have no evidence for or against them. I'm not testing one, however I did use a Fram filter to make the 2nd stage filter. I hacked up a new Fram filter to do it. I used some of the screen wire as backing and the paper / synthetic fiber filtration material to make my test filter. This filter is placed behind the test subject to trap any particles (most of them anyway; no filter is 100% efficient) passing through the test subject. I placed the 2nd (made from the Fram) filter with screen (don't want to suck a piece of paper into your engine or air meter) between the airbox and air meter.

Here is the view of the 2nd filter from the Airbox



The next photo shows the pieces apart. You can see the screen used for the 2nd filter. You can see a dirty 2nd filter after a test. You can also see the flapper door air meter (vane air meter), and the airbox top. The main filter sits between the airbox top and bottom.

Pieces and Parts



Did you see the dirty 2nd filter? Well that is the result of experiment #1. The test subject was the K&N air filter. Yes it let many particles pass through. The K&N was tested for 501 miles. For those that are curious, the test was conducted in Western WA state during the last week of November and December. All of the driving was on public paved roads. The climate here is damp during this time of the year and definitely not dirty or dusty. This is probably the best case scenario in all honesty. I was shocked by the look of the 2nd filter. I drive this car 6-8K miles a year. Many have asked if the black left on the filter is dirt or is it possibly oil residue. It is indeed dirt and not oil. The same type of deposits were left using a paper Napa filter which has no oil on it at all. That should be the end of that theory.

K&N Air Filter 501 miles Test #1



Filtration Test #2 Amsoil Air Filter 503 miles

The filtration test portion for the Amsoil air filter has also been completed. This was my first experience with an Amsoil air filter. I can say without hesitation that it is by far harder to service than the K&N air filter. You have to wash the filter using warm soapy water. Then you have to literally wring the water out, rinse, wring.... And then you have to let it dry which takes a long time. After that you have to impregnate it with the Amsoil filter oil which means squishing it into the foam pores by hand. Then you get to sop up the excess oil with a rag. It was messy and tedious. According to all the information I've ever read published by Amsoil and on their web sites their filter is the best at flow and filtration. Well the filtration portion is done, and the pictures don't lie. The filter was serviced properly. Here is the first photo of the test filter by itself.



Comparison photos of the Amsoil test filter next to K&N test filter


The first photo is using no flash from the digital camera and the 2nd photo is using the flash. The flash tends to really show how thin the dirt layer is, but the 2nd photo shows a better difference in the amount of dirt on the filters. In the Navy we often use color comparison as a valid test in various chemistry analysis procedures. One of the tests in particular has you distinguish between shades of gray and black. The test are accurate, and there is no way this test is false in this regard either. Let's have a look at those photos.






So are you surprised by the results? I was. I figured the Amsoil filter probably would filter better. At best, it is just as good as the K&N. According to the photos it is slightly worse. My wife who is a business major in college and sure has no stake in which one is which stated the Amsoil one was darker too. I put them both in front of her with the hand written sample text covered. She picked the Amsoil filter darkest, and she sure doesn't care about the results.

Filtration Test #3 Napa Paper filter at 498 miles

The results are in for the Napa paper filter. I always heard on the 'net that paper filters best. It does, but it isn't as superior as I thought it would be. The K&N doesn't filter nearly as bad as the horror stories say, and again the Amsoil was a disappointment. Here are two pictures comparing all 3. The first is with no flash, and the 2nd uses the flash in the same exact location and same wattage lighting as in the K&N / Amsoil comparison photos from above. My wife again established an order for filtration based on color not knowing which test filter is which, not caring, but putting up with my silliness anyway. She said the Napa filtered best, followed by the K&N, and last the Amsoil. She again reiterated that the Amsoil and K&N are very close as well. The Napa was clearly the lightest in color with the least particulate deposited.





The next Contenders

Also tested were the Jackson Racing two stage foam filter, a Mazda factory replacement, and a Baldwin filter. The Mazda is a fiberous filter, and so is the Baldwin. The Baldwin filter is the red one in the picture below and the Mazda one is white. The Jackson racing filter performed very similar to the Amsoil foam filter, and the other two fiberous filters (Mazda and Baldwin) performed much like the Napa filter. Using the shade of gray comparison test, the Baldwin may have a slight edge in filtration. A longer duration or bench test may show a more significant difference.



After 3500 miles of filtration testing, I am done. 3,500 miles of horrible power is more than I can bear. The secondary filter really kills flow and power above 4500 rpm, which is when a Miata starts to come to life. I've actually been done for a few months now, but haven't bothered posting the results until now. I tested the Baldwin filter twice and observed the same results both times to verify repeatability. Anyway, here are the final 6 test filters all gathered together with a picture, and another picture using the flash. From top left to bottom right, the test filters were: Jackson Racing, Amsoil, K&N, Mazda, Baldwin, and Napa. The Mazda and Baldwin filters were also tested for 500 miles.





Well there is a clear pattern on filtration ability compared to both flow and the type of filtration media used. The "high performance" cotton gauze and foam filters do not filter as well as some have claimed. I actually received an e-mail from K&N stating their filters filter within 99% of the OEM filters. This may be true, and 1% may not sound like much. I contend that 1% over many miles, may be important. Really, it is up to each individual to decide. The poorer flowing filters, remove more particles, and the better flowing filters remove less particles. If you think about it, that conclusion passes any and all common sense tests, so it is not surprising. There are many that will be shocked by the results, that should not be though. I've used high performance filters in the past, and I might again in the future. At the same time, I know that the stock OEM type filters perform very well in filtration and don't inhibit flow nearly as much as some think.

I know it will be asked.... The K&N was properly cleaned and serviced using a K&N filter recharging kit which I personally own (owned quite a few K&Ns). The Amsoil filter was serviced with Amsoil filter oil. The others will be serviced with the appropriate oil as well. The paper air filter will be installed.... I did have a question regarding the deposit on the filter possibly being oil. It is dirt. I took a piece of my 2nd filter test stock and put a few drops of K&N filter oil on it. The oil stays bright red on the filter as well. One person even mentioned the dirt in their area isn't that black. Well this is Western WA state where everything grows lush green. I live 90 minutes from full fledged rain forest and the soil here is black like topsoil. I guess I could take a picture of my white powder coated wheels turned black from road dirt if I had to. If you have a HEPA filtration air purifier in your home and have ever changed the HEPA filter, you will notice that it too is black. The Napa paper filter tested showed the same black deposits. Paper filters have no oil on them, so the oil hypothesis is a dead issue. In the e-mail I received from K&N, I actually got contradictory information on this point. They claimed that the deposit on my test filter was oil (it isn't), and then they said oil does not leave the filter and damage mass air sensors. Honestly, you can't have it both ways. Either oil leaves the filter or it doesn't. Oil will damage a mass air sensor if it gets on the sensor wiring. This is highly documented by TSBs easily available online.

Some have asked that additional filters such as Wix, Fram, and ITG foam be tested. Only the filters listed above will be tested. I do not have the funds, time or desire to test every possible filter. A clear pattern already exists. Foam is foam no matter who makes it. Fiberous filters are still fiberous filters, and paper is still paper. Sure there are minor differences, but in this test a clear pattern emerged based on basic filtration media rather quickly. I personally do not like the difficulties associated with servicing foam filters. I do enjoy the simple drop in of an OEM style filter. Imagine servicing and changing 5+ filters in one day for pressure drop testing. You begin to dislike serviceable filters quickly.

Originally Posted by Z_ealot

you also have to take into consideration the big difference between a sport bikes air filter and a sport cars air filter is that the bikes will always be more open to the environment where it can suck up more dirt from the road whereas the air filters on our cars tend to be tucked away behind the front bumper to prevent alot of that same dirt from getting to the air filters to begin with.

Originally Posted by gsxr750

One important thing you guys are missing is that, when most of these air filter and exhaust system companies started marketing their products. Most of the name brand products did actually provide some significant power gains, from the late 60's -80's. But this was the time when went from a 1969 425hp mustang to a 1980 mustang 2 with barely a 150 hp due to emission control. Unrestricting these low hp engines by changing the intake and exhaust and simple cam, change gave vast hp gains.
Most of this held true until the late 80's when car manufactures started producing true factory hi performane cars once again, a lot of research and developement went into extracting as much hp as they could and still make the car affordable and reliable to drive on the street.

So in the old days you could take a 200 hp chevy 327 in camaro base model, change the carb, manifold, install headers, change the came and you then had a motor with over 300hp.

Now jump to the late 90's - present factory sports/ muscle cars are producing easily 300-425 hp for most model and you still have these airfilter and exhaust companies trying to sell you on their 5-10 hp gains, marketing them as if your going to get the feeling of turning your pussy cat into a tiger with a few bolt on mods. Or that you will get the same power gains your father achevied on his 60's or 70's muscle cars.

What these companies focus on is the fact that a lot of the performance car buyers will do a few mods when they first get the car and target these buyers with these bolt on or decorative add ons to make their cars stand out from the rest. While making quick money off them.

Overall from seeing that even the cheapest drop cleanable air filters cost you about $110 a set and you can buy 2 replacement fram filters at wally world for around $18. With most of the responses showing that you only get about a 5-10 hp gains the best systems, it make more sense to stick with OEM or Frame quality air filter replacement.

One other note motorcyle air filters are behind the engine and a cars is directly in the front where it is actually bumber mounted where it is exposed to large amounts of air and dust coming into the engine bay area, specially with these front mounted bumper air filters, the splash guards they give you with these kits are meant to stop rain or water from entering the intake , not dirt.

Originally Posted by Z_ealot

i don't know about the sound on the FI CBE, but the exhaust i eventually wanted to go after later on down the road was the Powerhouse Amuse R1 titan exhaust, that thing sounds amazing and is light as hell to boot. from what i hear a gain of around 20whp can be had with the amuse exhaust, but it is pretty expensive.

Originally Posted by gsxr750

Look at the old test results by motor trend with 370z base model vs. the 370z nismo and even with the extra hp the nismo had, it performed worse than the older 370z base model. So I really doubt if a 5-10hp increase your driving experience that much from a CAI or airfilter change.

Originally Posted by Skeeterbop

If you don't want an aftermarket filter fine, but your opinions aren't going to change my mind. I'm almost at the point of saying we are being trolled.

Originally Posted by Skeeterbop

It wasn't due to the air filter/exhaust though. I'm with Z_ealot, I'm going to agree to disagree. It looks like you are trying to convince everyone that your way is best, to each their own i say. If you don't want an aftermarket filter fine, but your opinions aren't going to change my mind. I'm almost at the point of saying we are being trolled.