Interesting read RE: K&N Filters...
 

From a Bimmer site...:D Food for thought... Let the games begin...

Jim Conforti (AKA the Land Shark) did some testing:
This was a scientific test, not one done by filter manufacturer X to show that their filters are better than manufacturer Y. The test results are pretty irrefutable as the test lab tests and designs filters where "screw ups" are absolutely NOT allowable (I can't say any more for security. Think "Glow in the Dark").

A scientific test was done on TEST filters where air was loaded with ACCTD (some standardized "test dust" called AC Coarse Test Dust) and sucked through the TEST filter then through an analysis membrane. From the Quantity of dust injected and the amount that gets through the TEST filter and is then captured on the analysis membrane we can calculate the efficiency of the TEST filter in Question.

BMW Stock Filter, Eff. Area of Media: 8.4 sq ft.
K&N Replacement, Eff. Area of Media: 1.6 sq ft.

The filters are the SAME size. They both fit in the STOCK BMW M3 airbox. The difference is that the STOCK filter has 65 pleats 1.5" deep and the K&N only 29 pleats each 0.75" deep.
Now, remember this ratio: " 5.25:1". It's the ratio of the AREA of STOCK to K&N. It's very important and will come into play later.

The STOCK filter efficiency started at 93.4% at 0 loading and increased to 99.2% efficiency as the loading increased to a max tested of 38.8 gm/sq ft of dust.


The K&N filter efficiency started at 85.2% at 0 loading and increased to 98.1% at the max tested loading of 41.38 gm/sq ft.

Now, I hear you. "Jim, that's only a FEW PERCENT". But is it?

Let's look. If we had 100 grams of dust on a new BMW filter we would let through a total of 6.6 grams of dust in. If we used the new K&N filter we get 14.8 grams of dust. That's 224% (TWO HUNDRED TWENTY FOUR PERCENT!!) more dust ingested initially, stock vs. "free flow" and this ratio is pretty much held. Somewhere between 200-300% more dirt gets "ingested" anywhere across loading equivalence. The more INTERESTING thing is when you look at what happens to the DP or Differential Pressure at a constant airflow as you dirty both filters equally with time.

The test used a rate of 75gr of dust per 20 min. Here's where the AREA difference comes MAJORLY into play. See, even though the BMW filter flows a bit less at the SAME loading, it also LOADS UP 5.25 times SLOWER due to it's LARGER effective area. So what happens is that the K&N initially flows better, but as the dirt continues coming in, the K&N eventually flows WORSE while still letting MORE dirt in.

Now, does any of this additional dirt cause problems? I dunno. I suppose we could have a few people do some independent oil analyses on different motors using both K&Ns and Stock filters. Get enough of them, and you'd have a good statistical basis. For me though, it's simple: More DIRT = BAD.

The additional short-term airflow might make sense on a track car. IMHO, it doesn't for the street.

-- Jim Conforti

K&N Response:

This is incorrect. The difference between 99.2% and 98.1% (his results) is 1.1% not 224% as he states!!! (bmwE34.net: who didn't go to school... Jim was measuring the amount of dust that goes inside the engine). Furthermore, does he realize that 96% meets OEM standards? K&N has been around for over 30 years and we sell over 2,000,000 units a year. If there were any sort of problem, one would think we would know by now and so would everyone else. One Internet "expert's" opinion is not reason for concern and should be taken loosely at best.

That information is 100% untrue. Don't believe all you read on the Net. Most opinions are not based on any sort of factual evidence. Our filters are tested by an outside, independent laboratory. They have been proven to stop at least 99% of particles on a SAE dust test. This test uses particles as low as the 0 - 5 micron range and goes up to 20 microns.

For comparison, a paper filter also stops 99% on the same test and the OEM minimum standard is 96%. Foam is generally the worst media with a typical efficiency rating of 75 - 85%. To get higher ratings, the foam must be more dense and therefore way more restrictive. The "tack" characteristic of a K&N allows for increase filtration without loss of flow as well. The testing procedure used is SAE J-726 using ISO Test Dust. This test is the standard of the air filter industry. The test procedure consists of flowing air through the filter at a constant rate (airflow rate is determined by the application) while feeding test dust into the air stream at a rate of 1 gram per cubic meter of air. As the filter loads with dust the pressure drop across the filter is increased to maintain the prescribed airflow rate. The test is continued until the pressure drop increases 10" H2O above the initial restriction of the clean element (in this case .78" to 10.78" H2O). At this point the test is terminated. The dirty filter element is then weighed. This weight is compared to the clean element weight to determine the total Dust Capacity. The amount of dust retained by the filter is divided by the total amount of dust fed during the test to determine the Cumulative Efficiency.

The K&N filter achieved the following results:
- Dust Capacity: 305grams
- K&N Cumulative Efficiency: 99.05 %

Holding the filter to the light is useless, pin holes are normal.
That is what makes a K&N filter. There are actually hundreds of microscopic fibers that cross these holes and when treated with oil, capture and hold the very fine particles. On the same hand, they allow the filter to flow more air than paper or foam. The filter is 4 ply cotton gauze unlike some competitors synthetic material filters. The synthetics do not have the very small fibers that natural cotton does. Also, the oil can be pulled off of a foam filter contaminating electronic sensors. It will absorb into cotton and stay in the media. In fact, Honda and Toyota only recommend K&N filters when using aftermarket high flow filters as K&N is the only brand of filter the oil does NOT come off of. They will not cover a failed sensor if foam filters were used. We got started over 30 years ago making filters for motorcycles and off road racers. The filters did so well that these guys wanted them for their cars and trucks. We started making filters for these applications and here we are today. If they did not work, we would not still be here and growing every year. We now make filters for Chrysler/Mopar, Ford Motorsports, Edelbrock, Rotax Engines, and Harley Davidson. We come as original equipment on the 2000 Ford Mustang Cobra-R. We even made filters for the Apache helicopters used in Desert Storm because of maintenance problems with the original paper design. If they work in these conditions they will work for you.

Rick from knfilters.com

Another interesting note seen in the March 2004 Panorama pg. 58 is the following statement "A BNC or K&N filter in the car can cause a problem with the oil on the filter passing through and ending up on the [MAF] sensor; causing a bad reading.

The above is refering to a Boxster, but still interesting that they claim oil in the filter may be going into the induction system.

I tend to think the best air filter is an often-changed OEM paper version.

Inexpensive insurance as an ineffective air filter can destroy an engine.

Its pretty well known, I always thought, that K&N filters both let in more dirt and the oil tends to negatively impact MAF sensors on cars so equipped.

Its a big problem on Audi S4's, I know. Everyone I know who had K&N's on their car kept having to replace one MAF after another until they went back to a stock filter.

Every manufacturer has a claim. I don't think the " ..we are still making them" argumant is very sound since Ford made alot of Pintos and Mustangs with fauty fuel tanks. Since there are no recalls for bad after market parts we are left to wonder if the filters work. I have to believe the ads bacause I have no other source of information.

I recently saw an ad for an Amsoil foam fiter. They claim that it filters better and flows very good (twice as good as stock), they did the same dust tests against a K&N filter and a stock filter. Their filter was better at removing dust and flowing air.

http://amsoil.com/products/ts.html

the problem is that a bad filter will not cause a motor to fail right away. we cant go, "damn you, k&n, look what your crappy filter caused!" it is pretty easy to get a bunch of kids all caught up with that on the counter display with the ball that floats on a pocket of air. the ball always floats higher with the k&n. just that every old timer original motor car with hundreds of thousands of miles always have the stock filter. for years i had a K&N on my pickup. everytime i clean the filter, i always take a damp cloth to wipe the airbox out. it was an epiphany, when i realized "WHY!". k&n suck.

Pipercross all the way

Ohh yes!

Wolfram wire in MAF that is used to measure air mass flow is heated to 700 degrees Celsius every time you shut off the car, to burn eventual residue. Problem is, when it gets coated with oil and then heated to 700 deg. the oil will coke and eventually either degrade and snap the wire or isolate it from surounding air.

A few comments from a science friend of mine:

1. If the K&N efficiency was 85.2, and the stock 93.4 at zero load, they both failed, since as the K&N response points out, the acceptable level is 96%.

2. The data doesn't support Jim's assertion that the stock filter holds more dust because of the plethora, myriad, or even multiplicity of pleats. The K&N filter conked out at 41.38g/sqft, the stock only held 38.8. Doing some math here, the efficiency per square foot for the K&N is 25.8625, while the stock filter is 4.619047(repeating decimal).

The conclusion I draw here is that the K&N keeps filtering when the air is 106% as dirty as with the stock filter, and does so with less than one fifth the material.

Okay, it's time for a real world test.

Let's run the left side of a 911 engine with a paper filter, and the right side with a K&N.

Now lets go run out test car like a banshee through the Mojave desert, through gravel forest service roads in the Colorado mountains, and enter in in the OTC. After a few hundred thousand miles, we'll tear down the engine, and inspect for wear.

My car is Motronic, and only uses one filter. Anybody with Webers want to donate your car?

Since running with no filter at all on a stock 3.2 doesn't make any more power, why would anyone bother with a K&N in this application?
-Chris

I would love to have a real test. The test mentioned by Amsoil seems to be objective but it is hard to believe companies ads. This would be a great topic for Panorama or Sports Car or GRM or....

I think the only advantage of a reuseable filter is that it is...reuseable. No thrown filters. No land fill junk.

It also seems that the longer between cleanings the better because filtering drops when clean.

I have an almost new K&N filter for 3.2, with cleaning kit and almost full bottle of oil....for sale.

PM me if you are interested. Make me an offer.

The PO purchased it. I removed it immediately upon purchasing the car from him.

sonic

It's the same reason someone would buy an off the shelf chip or swear on their momma's life that gas from Station A is better than Station B, after you had just witnessed the same tanker deliver gas to both stations.

K&N has done what many others do, exaggerate performance claims and try to sell their products based on the "coolness" factor.

The "coolness" factor evolves the older you get, thank god...

Run faster, Jump higher!!

Originally posted by ChrisBennet
"Since running with no filter at all on a stock 3.2 doesn't make any more power, why would anyone bother with a K&N in this application?
-Chris"

If you take the muffler off and doesn't make any more power why bother with a performance muffler? :D Just playin...

Apples and oranges. They weren't the same test. They didn't use the same dust. You can't compare the filter efficiency results against the SAE standard.

Neither filter 'conked out' in the first test. The poster does not give the criteria used for determining when the test ended. In fact the difference betweer 38.8 and 41.38g/sq ft is only about 6%. It could be that this test procedure is to stop in the neighborhood of 40g/sq ft. We'll never know.

However if you look carefully at the units he is saying that at 41.38grams per square foot of filter media the K&N filter was working at 98.1%. This would mean that after being loaded with 66.2 grams of dust (1.6sqft * 41.38g/sqft) it was passing 0.07grams per minute (70g/20min * 98.1%)

The Stock filter was tested until it was loaded with 38.8 grams/sq ft of filter media. When loaded with 325.9 grams of dust it was functioning at 99.2%. So it was passing 0.028grams per minute.

So the stock filter was took 4.5 times as long to get loaded to roughly the same level on a per area of filter basis and at the end was passing about 40% of the dust that the K&N filter was passing.


This conclusion is based on the idea that the filters stopped filtering by the end of the test. This is not the case. Both were filtering still at the stated percentage. I believe that you have also mistaken the 38.8gr/sqft and 41.38g/sqft as measurements of the amount of dust in the air, but that would be g/cubic feet. They are talking about loading on the filter surface.

What I don't understand is how in the first test the efficiency was measured at the different loading levels. Jim described the method as using a secondary filter to capture the dust that passed the test filter, then somehow the amount of dust on the secondary filter was weighed or measured. This method would only produce and average efficiency for the whole test.

The K&N representative does not present his test results in context with test results from stock filters. Also nothing here addresses how a K&N filter performs at varying times after the oil has been applied. Is it as effective after one month of use? One year?

I don't believe that anyone is claiming that under the SAE test conditions that a K&N filter fails to meet the 96% criteria.

Mike Benefield, PE

I can't understand why anyone would run a K&N filter in a stock airbox, but I can totally understand why you'd want to be rid of the stock airbox. A cone filter gives you better maintainence access, and is easy to remove to get out of the way, plus with a cheap piece of pvc elbow you can get it out under the grill where there is cooler air. Same reason you'd backdate your heat, cleans up the engine compartment.

I could really care less about all of these dust comparison tests, as what they all ignore is whether the "extra" dust passed thru the oiled filter is actually harmful, as opposed to assuming that its harmful. I submit that in the real world, regular runs to 6k probably have more affect on ultimate engine life than which filter is used.

There are two reasons I posted this... one, simply to see the response...two... to see the response.

What interests me in this whole issue are how the "opinions" of various sources are ascertained. Most are spouting internet rhetoric, or passing on false info riding the band wagon. Both on the pro side AND con side. Personally the subject is interesting, as it GLARINGLY shows the overall distrust of corporate claims. While some of these are indeed true, I think most corps get the bad rap when it comes to "claims" of product usefullness. The reality of ANY test that is based on stats is they can be "tweeked" in whatever way to make a point. I think it's somewhat sad that most people (to include myself) tend to fall into the "believe the negative" catagory and totally disregard the positive, simply because it's a large corp "making money".

We will never know whether or not the K&N is the garbage filter, or if paper is the engine savior... because as the previous post stated, the reality is that MOST engines get far more abuse from lack of care, than any filter could cause.

BTW, I've had a K&N type of filter (MSDS cone system) on my car for 5 years. Never an MAF problem, nor has there ever been any sign of dirt or oil residue in the intake. My guess is, like most problems that occur in the auto world, that issues arise from USER related errors or incompetence. My opinion of the filter is, I've never had a problem, and my mechanics, racers etc. that I know, don't have any problems with them either.

Fun thread!!!

re opinions, see my post today on the msd thread.

But "reality of ANY test that is based on stats is they can be "tweeked" in whatever way to make a point." is not true. Many valid statistical analyses are too clear to "tweak" -- not all. Your stmt is too extreme.

re user error -- Good product design compensates for user error. There is no way a paper filter will oil up a MAF wire. I'm not claiming paper is better mind you.

Fair enough on both counts... I just think the internet, for all of it's good has some pitfalls of "misinformation" that tend to be looked upon as the ABSOLUTE truth (both sides mind you) without further analysis. Not always, but often.

This K&N thread was not meant to prove anything, just to see the reaction to "stats" from both sides. And, as I thought, most of the K&N info was either ignored or called as incorrect, or misinformation. There are always two sides to every issue. Otherwise our spirited chip debates would never occur!!!

http://www.pelicanparts.com/support/smileys/wat6.gif