AMSOIL Two-Stage Air Filters vs. K&N Air Filters

K&N Air Filter

For years now K&N has always dominated the performance market and really been considered the upgrade choice for anyone wanting to replace their OEM Air Filter with a better performance one. Paper Air Filters, while very good in filtering out dust and dirt, are very restrictive in the air they allow into the engine. This restriction can starve your engine from the air it needs to create the power it is capable of. To get that power, a free flowing air filter is needed, one that doesn't restrict the air path as much allowing the air to rush into the intake when needed. K&N has been the leader in this market for years, creating a very free flowing, less restrictive filter. Often a few extra HP can be gained just by switching out the Paper Filter for a K&N.

However, to accomplish this, K&N uses oil wetted gauze with rather large openings allowing dirt to pass through it much easier. Larger particles will stick to the gauze, but the more fine dirt and dust will freely pass through it into you engine. This can act like fine sandpaper and cause wear. In the K&N advertising, they claim that this dust catches on their material with their depth cleaning, however, if you were to hold a K&N up to the light, you can easily see the light shine through the holes in the material. If sunlight passes through that easily, imagine the fine particles of dust. K&Ns do filter better over time, but that is because these holes end up filling with dirt. When this happens, the air passing through gets restricted more, causing the claimed air flow to become less. K&N is a good performance filter, but there are other choices.

AMSOIL Two-Stage Air Filters

The AMSOIL Two-Stage Air Filter is a double foam layered filter. In the summer of 2003 the entire line of Two-Stage Air Filter, now also called Flowzair, were revamped using better materials. Even before these changes, the AMSOIL Two-Stage Air Filter performed well. These filters are also tacky with an oil AMSOIL makes, like K&N has for their filters. The theory behind these filters is similar to that of the K&N. Air passes through the outer layer of foam first. This foam has larger openings and catches the larger dirt particles. The passages passing through the foam are not a straight through design, so the air needs to pass around the various foam obstructions to get through. While the air can wind freely through these passages, the heavier dirt will be caught on the oiled foam as it hits the passage sides.

Once past this first layer of foam, the air enters a second even finer foam that performs the same operation until the air entering your engine is 99+% clean. Below shows the basic makeup of most all of the new AMSOIL Two-Stage Air Filters.

Differences

Both K&N and the AMSOIL Two-Stage Air Filter use a process called depth cleaning. A paper filter captures dirt on the outside, with small openings that allow the air through. This is why you might hear of a micron rating being given on the dirt particle size these types of filters are capable of capturing. Depth cleaning involves catching the dirt not just on the outside of the filter, but as it passes through the filter. A K&N filter typically is about 1/4 of an inch thick, while the AMSOIL Two-Stage Air Filter can be as much as a full inch thick with both foam layers. Which filter do you think provides more depth cleaning? Also as both of these filters collect dirt, they react differently with the air flow. As mentioned above, the K&N starts to get restricted. As the filter gets dirtier, the less flow the K&N can provide. The AMSOIL Two-Stage Filter on the other hand is designed to hold this dirt without it restricting air flow. The AMSOIL Two-Stage Filter has a higher efficiency and holding capacity. Flow does not get effected until it's close to 95% saturated with the dirt it has collected.

Feedback

Since selling the AMSOIL Two-Stage Air Filter over the past several years, I've heard numerous stories from both other Dealers in the business far longer than myself, as well as racers in the performance community. The comment often mentioned is the amount of dust found inside the intake that the K&N lets through, especially in heavy dust conditions such as offroad and motocross racing. On the other hand, they have commented on how clean the intake was after switching from K&N to the AMSOIL Two-Stage Air Filter and in some cases even noticing more power. A Direct Jobber I work with said he has sold these filters for 23+ years for various applications and has done "the white glove test" on many intakes, and has yet to see any dust on the glove. While this might not be scientific, there is a visual difference between the two filters when this is done.

Differences in Show Displays

Recently I was made aware of a test K&N performs to show that their filter can outflow any filter on the market. This is what they are famous for and by all appearances of this test, they are correct. However, information coming from a source who once worked for K&N, these display machines can be set to fail any filter. They can even set the machine to show the K&N filter flows better than with no filter at all!

We as Amsoil Dealers also have a machine that can show both the cleaning and flow of both filters. Typically this machine draws air down a clear tube with white fabric at the bottom of the tube to show what dust passes through the filter. On top of the tube is a fitting to place various filters on top. When placing a paper filter on top and sprinkling laboratory dirt, which is very fine and used for this type of testing, you cannot see any dust pass through the filter and accumulate on the white fabric. Using an Amsoil filter the results are the same. Place the K&N filter over the opening and perform the same test, and a visible "puff" goes down this tube leaving a dark spot on the fabric. This dirt would have just gone into your engine!

The second part of the test involves flow. Using a few different fittings on the same machine, the air now escapes through another tube holding a ping pong ball. Without any filter the ball shoot to the top of the tube and is prevented from flying out by a crossbeam. Place a standard paper filter on the unit and the ball drops to the bottom of the tube, showing that the machine is not able to draw enough air through it to push the ball up the tube. Place the K&N filter on the machine and the ball hovers on average around 1/2 to 3/4 up the tube. Now using the AMSOIL Two-Stage Air Filter the ball travels to the top of the tube. There are no special settings to this machine that we can adjust to skew one brand of filter to be better than another. And using no filter at all will always flow best and there is no way we can show otherwise.

Other Manufacturers Are Aware

The dust that passes through the K&N is also known to many manufacturers. In fact below is a snapshot of a Web Page that used to be on the Cummins Diesel Site saying not to use a K&N with their engines. This page is no longer on their site, but it shows they are aware of the situation, enough to have brought up the topic on their Web Page.

The Choice is Yours to Make

Ultimately the choice is up to the user. In some cases the AMSOIL Two-Stage Air Filter might not be the best application. If you run a highly modified engine with a larger amount of air flow needed, the AMSOIL Two-Stage Air Filter might not be the best choice and a specialized racing filter would work better having been designed to handle the higher flow demands. Typically the AMSOIL Two-Stage Air Filters are designed to replace the stock OEM filter, but can be used in many racing applications.

K&N is still a good filter. But are they the best? You decide.