K&n Filter

[Iconic Bionic]

Hmm. This was interesting. Sorry its a bit long!

Air Filtration and Flow Test

As automotive enthusiasts, we are always looking for ways to increase the power output of our motors. Many aftermarket companies now manufacture and offer high performance air filters. Most all claim a power gain through increased airflow and some claim better filtration as well. In this test, many air filters will be compared. I personally have owned various makes of performance automobiles. This particular test is being conducted using a 1992 Mazda Miata with a bone stock engine (can't wait to modify it personally). I have many different turbocharger parts and components collected waiting to modify the Miata. The air filters tested include a Napa Gold, Amsoil two stage foam, Jackson Racing two stage foam, a Baldwin fiberous, a K&N, and a Mazda factory replacement.

The air filters will be mounted in the stock air box and filtration tested by placing a 2nd filter (after filter if you will) just before the airflow meter. A picture, as you will soon see, is worth a thousand words and shows this setup. A water manometer will be used to test pressure drop across each filter. Obviously the filters with lower pressure drop flow better, and have the potential to yield more power given the engine actually needs the airflow increase. The pressure drop across each filter will be measured in inches of H2O (water). The pressure drop will be from atmosphere using the stock Miata induction system to the air box just after the filter. 1 psi of pressure = 27.7 inches of water for reference.

I have a degree in mechanical engineering and am currently pursuing a master's in engineering management. I have been around the automobile all my life, and will be obtaining certification as an ASE certified mechanic this fall (for fun). My father worked in the automotive test industry my entire adolescent life. I've also spent much of my life at the race track, either racing as an amateur or with my father who was a crew chief for a stock car racer many years. He also was a crew chief at the 24 hours of Daytona and LeMans twice. I regret not being able to go to LeMans to this day. I'm a certified gage calibration technician, certified quality assurance inspector, certified as a refrigerant worker by the EPA, and work in the Navy as a mechanic in nuclear propulsion. I like to think I know a few things about machines including automobiles, but there is always something to learn.

I choose to conduct this test because of the conflicting information I see in advertisements and have read on the internet. Everyone claims that their filter flows the best, and removes the most dirt. If you think about it, flow and filtration ability are actually linked. A solid piece of metal would prevent any particles from entering the engine, but it wouldn't flow any air at all. On the other hand, the screen used on a window screen will flow well, but won't filter well at all. So if you think about it, the best flowing and best filtering is really contradictory in claim. I wanted to find out which filter really does filter the best, and which one really does flow the best. I have used almost every brand and type of air filter over the years including K&N. I had not used a foam filter until conducting this test. I have used every manner of off the shelf fiberous or paper filter.

There are basically four types of filtration materials currently in use for automobiles: paper or other fiberous (some appear much like fiberglass), foam, cotton gauze and stainless steel mesh. This test has used the first three, but not stainless steel mess. Steel mesh bathed in oil is some of the very first filtration materials ever used in an automotive application. There is a reason they were abandoned for paper in the '60s. I find it surprising that some aftermarket manufacturers are touting them now. In the links at the end, there is an interesting test of a stainless mesh filter.

The filters in this test were tested for both flow and filtration. The pressure drop across a filter is a good indication of its ability to rob the engine of needed airflow and hence power. Obviously the air filter with the least pressure drop is the highest performing. For the filtration test, I used a secondary filter after the filter being tested to catch any particles that passed through the first filter. The secondary filters were made by cutting apart an off the shelf Fram carburetor filter. The particles passing through the filter being tested leave a deposit on the secondary filter. The lightness or darkness on the secondary filter is an indication of how much dirt is getting through the filter being tested.

The differential pressure test was performed using a water manometer where one psi of pressure is equivalent to 27.7" of water. The differential pressure was measured between atmospheric and the pressure drop after the air filter in the stock airbox. The max pressure drop in this test was seen at only 7.0 inches of water or 0.25 psi. The factory airbox and piping with no filter yielded a pressure drop of 5.0 inches of water or 0.18 psi. That means that the worst filter in this test only caused a pressure drop of 0.07 psi. In my opinion, this means that if you are picking an air filter based on performance, you probably aren't doing your car any favors. For the record, the K&N was the best flowing filter. Of the 3 types of media tested, the cotton gauze type filters flow best. There are other brands besides K&N for sale, of which most are probably made by K&N for resellers. Foam air filters flowed marginally better than paper.

The filtration test has been the cause of much argument and debate in some circles. Many contend that a color comparison (comparing shades of gray) is not scientific or appropriate. Again, this is a very low budget test, and there are other scientific analyses where color comparison is valid. In water chemistry a color comparison is often used to determine concentrations as low as parts per billion. Search for information on titrations (of which some are by color) or color comparators. In chemistry the color is compared to a known standard of specific ion concentration by color. If you have ever played with a fish tank chemistry sampling kit, then you have done color comparison yourself. In this air filter test, no attempt is made at determining actual concentration. A color comparison is used to determine real world filtration ability. Each test filter was used in the same car, on the same roads for 500 miles. The darker deposits indicate poorer filtration, and lighter ones better filtration. That said, both the cotton gauze type (K&N) and foam filters (Amsoil & Jackson Racing) showed the same levels of filtration. Both performed poorly compared to the fiberous or paper filters (Napa, Baldwin, and Mazda).

If you are interested in the filtration pictures or pressure test data, follow the links provided to my other pages. You will also find links to other tests, which I found interesting on the web. In the end, paper or fiberous filters do remove more particles from the air before they enter your engine. The cotton gauze filters indeed offer better airflow. You have to decide for yourself whether you value ever last ounce of power or filtration. I cannot, nor will I make this decision for you. I do know that on a relatively stock car with a properly sized air filter, you indeed have very little if any performance to gain by swapping filtration material.

Edited 25/09/06 05:59 AM by Iconic Bionic

[RAP1D]

I thought it was common knowledge that K&N filters let more crap through than foam and paper elements...

Anyway, I wouldnt panic too much about some crap going into the motor, I've had a good chunk of turbine go through my last cars motor and it was fine... I'm sure there's plenty of Ts on this board that have some fine shavings going through their mototrs, let alone some super fine dust...

[Iconic Bionic]

I'd be thinking that regular oil changes would alleviate issues of trees and wildlife getting into the engine.

Every 7,500KMS for me. I know others or more frequent.

[937]

I still remember some years ago, some Racing Teams used to put Ajax down the carburators to bed in the piston rings.!!!!!!

Very fine dust will do the same to your engine.

[tmac450]

The proof of K & N filters not being effective dirt stoppers is on the box they come in. K & N themsleves recommend the use of an oiled foam over sock in dusty conditions.

As far as the damage caused, I mentioned earlier that I race dirt bikes and dust and dirt is the major reason for mechanical failure in the sport. Some fools have been known to try K & N on their bikes with disasterous effects (such as destroyed valve in the first event used).

All dirt bikes come with foam filters and it is the oil that does most of the work. That being said, most bikes (especially the Eurpopean ones) need to have filters with finer foam fitted as the Australian dust is finer (due to our dry climate) and it is essential to clean and oil the filters every ride.

To say that dirt in your motor has no effect is just putting your heads in the sand, in the Australian 4 day Enduro a couple of years ago, nearly all 4 stokes failed to finish due to the dust getting into the motors. Bikes tend to be tuned to a higher degree than most cars in order to maximise the power from a small motor, and they only have one cylinder and up to 5 valves so any valve damage is quicker than cars. Just because your car has multiple pistons and valves and dust damage is spread out and longer to become evident, doesn't mean that it doesn't happen.

V8 Supercars don't use foam because it is controled (as are the Dunlops), in fact they are free to use whatever filter and filter design they find the most benefit from, they use foam because they don't need their highly tuned motors dropping valves because of dirt getting in.

As mentioned above, the actual air flow has little to do with the idea of an after market filter, the element is there purely to stop dust. The design of the intake, pod and plumbing plays a much greater part in power gains or simply the removal of the restrictive air box which reduces the available air volume. Also, some cars have know to drop power with the addition of after market filters that offer too much air flow as many motors perform better with a little resistance (similar to exhaust back pressure. Try breathing through (or blowing through) a vacuum cleaner hose, then a straw. The vacume hose is easier, but increase the pressure and note that there is no power through the vacuume hose because there is too much air to move (which is why power drops at altitude due to thinner air). With motors it is a similar thing with a combanitation of air pressure, flow patterns and available air. This also needs to be combined with tuning as a motor will only take the air it needs.

[RAP1D]

So any evidence of street driven cars with dead motors from using KN filters?

[BFHOON]

if this adds anything to the debate.

I have 255 rwkw using the stock filter after 10000 kms use.

[RAP1D]

What psi Hoov?

[BFHOON]

9 psi untill I get squirters

[tmac450]

So any evidence of street driven cars with dead motors from using KN filters?

←

Don't know. There is a few cases where cars using aftermarket filters (unnamed) that have sucked in alot of water (modified air intakes or filters dropped lower down), flame outs setting fire to foam filters and causing engine fires, filters collapsing and the elements egtting sucked through the motors, coming loose (or poorly fitted, letting a heap of crap through and causing valve damage.

I a car club that I was involved a few years ago, we did a few dyno tests on a few cars and looked at filters, exhausts, octane booster, spark plugs etc and found the results to vary wildly from car to car.

A 92 Honda CRX dropped power when an K & N was fitted, but showed slight gain with a Uni-Filter, but a brand new paper element was just as good. My EFII XR 6 dropped power with any aftermarket filter, an exhaust made no gains, but a change of plugs saw a 5kw gain at the wheels (NGK V Groove). Later on my AUII XR6 ute, a Uni-Filter ram pod and cat back exhaust showed reasonable low down gains while a change of plugs saw a power drop (by then Ford had switched from Motorcraft plugs to NGK). Essentially these last two had the same motors, but the introduction of VCT and different tuning methods changed the outcomes from EF to AU.