The K & N... and other aftermarket air-filters,
including the UNI brand filter.
© Copyright, 2014, R. Fleischer
NOTE: The very extensive in-depth FULLLY CHARTED report on the K & N laboratory test information of 2004 has been removed from this article (I have incorporated LINKS to the charts, etc., in this version). I had long ago obtained formal permission to post various charts & tables; but unfortunately, over the last several years, the links to the various articles & information & the backup information for my own & others' charts & tables have been OFTEN either removed or moved to different addresses or to other sites that I had to do a lot of work to even find. About 70Mb of data was originally posted in charts, etc., here. I do NOT want to post anything I cannot have YOU easily confirm. On 11/20/2013 I gave up trying to keep up with the problems.
I give the most pertinent information in the article you are reading. As a minor note, the copyright to this article you are reading is now 100% mine.
A considerable time after I had removed maybe 80% of the charts, etc., I found the following link!.....which had most of them posted. The following LINK was still on-line August 10, 2016, and contains MANY of the pertinent details & charts, from the above noted tests. PLEASE READ THIS LINKED ARTICLE....and then proceed to read the rest of my article.
http://www.nicoclub.com/archives/kn-vs-oem-filter.html (archive, dated 2009). May be the same, or expanded, compared to the above link page.
Preliminary: This is from an exchange on the Airheads LIST, edited strictly for clarity. " ... although the Uni Filter sounded good until they stated that I may have to rejet since their filter provides greater air flow than the stock... Any Hedz have experience with the Uni Filter and rejetting? OK....here are what I, Snowbum, Mr. Intense Curiosity, personally did, besides all the various filters I inspected on customer bikes (and the insides of their engines!)! Information on the outside formal testing by an industry-accepted laboratory, follows this section.
K & N was founded by Norm McDonald & Ken Johnson, in 1957. They were motorcycle racers who met & opened a motorcycle business, called K & N Motorcycles, in Loma Linda, California. Primarily a service shop, they eventually took on Royal Enfield & then Yamaha. They hired a teenaged dirt bike rider, Malcolm Smith (yes, the one & the same!!) to work in the shop. Over the years, they opened other motorcycle shops, selling many brands. In 1965 Norm & Ken branched out into selling handlebars, fenders, fork braces, etc. Later they sold insurance, had a beer bar, etc. In 1966 they started selling the K & N filter, which proved to sell, & still does. These filters WERE OK for SOME racing purposes, if properly installed (vibration could foam the fuel on carbs, on the cone model filters, just one of many considerations), and if tuning for them was done properly; this is because the early filters were for racing, and very different from most of their filter uses now. You must retune on a BMW Airhead if you go from the central filter to the individual K & N type. In 1971 the partners split up, & Norm moved to Tulsa, OK, opening bike dealerships. Ken kept K & N Engineering. UNfortunately, K & N filters are used by street riders, & they are not, IN MY OPINION, good for street bikes, letting too much abrasive dirt into the engine. They ALSO do NOT flow more air than stock pleated paper filters....& this air flow & filtering subject was the huge section of laboratory results that I removed the links-to in this article on November 20th, 2013, due to the problems with those various links over the years, see top of this article note. My private files have these charts & tables. Since 2013, as noted well above, there are other sites hosting the information, so the vast majority is still easily available....AND.....I've posted various charts in the article you are reading, below. I also, in the below article, explain how I did my own testing, to be sure that the Laboratory testing was accurate for Airheads.
Snowbum stated: "BMW filters have a vastly larger filtering area than required". This means the BMW filter is not strangling your engine. This means your engine will demand no more air with a supposedly better flowing filter than it does with the BMW filter & this means you don't have to rejet. "..... (((note: need for rejetting for filters replacing the stock filter AT THAT LOCATION is usually NOT necesssary)))
***Snowbum notes that if you modify the intake system and replace it with individual filters at the carburetor intakes, you WILL have to rejet, and it is due to the disturbance of the intake pulses that BMW so carefully designed for. This is very different from air flow obstruction. A rather complete treatment of intake tuning is here: http://bmwmotorcycletech.info/InExTuning.htm
I DID TESTING. Changes to engine & rpm would have to be very big changes for the stock BMW filter to be inadequate for air flow, assuming a reasonably clean, to moderately dirty filter. My supercharged /5 went for normal mileages between STOCK filter changes; around 20K for me (I rode in somewhat dusty areas often, otherwise the filter replacement would be at a much higher mileage);....and, I did measurements on it in the same way I did much later to my first R100RT:
I used an old super-sensitive aircraft gauge that is a dual type (separate elements, twin needles). I also have a differential altitude instrument that is even more sensitive, & reads out in inches of mercury. ANY of you with ANY type of manometer, gauges, whatever, can pretty much duplicate what I have done. With one side of my dual gauges connected to the intake side of the filter, the other side connected to the outlet, I could measure the difference across the filter. If the 'piping' is properly positioned to avoid venturi & coanda, etc., type of effects, this really works rather well. I have tested the stock filter on my R100RT when brand-new and when it had over 20,000 mostly road, but some off-road dusty miles. On the SAME R100RT, I also tested a brand-new K & N filter that I specifically purchased for measurements. I tested the K & N before oiling & after oiling it with K & N FilterCharger red fluid. I had an old customer's K & N filter that was quite filthy, & tested it. I also tested it with a dirt bike foam surround I added. I also tested a BMW 2002 car filter (round type), that mounted on an aluminum plate, sealed to the top of the lower part of the rectangular R100RT airbox. That filter was noisy, susceptible to water damage (I never made a hat for it), but the results of ALL my testing was pretty clear.
This is from an exchange on the Airheads LIST, edited strictly for clarity.
" ... although the Uni Filter sounded good until they stated that I may have to rejet since their filter provides greater air flow than the stock... Any Hedz have experience with the Uni Filter and rejetting? OK....here are what I, Snowbum, Mr. Intense Curiosity, personally did, besides all the various filters I inspected on customer bikes (and the insides of their engines!)! Information on the outside formal testing by an industry-accepted laboratory, follows this section.
OK....here are what I, Snowbum, Mr. Intense Curiosity, personally did, besides all the various filters I inspected on customer bikes (and the insides of their engines!)! Information on the outside formal testing by an industry-accepted laboratory, follows this section.
Some conclusions, notes, advice, etc.:
Our motorcycles, with the original filter replaced by a standard K & N, do not need rejetting. This means that the stock filter, in the stock location, would be replaced by a K & N mounted at the same location, and fitted the same way as stock. I do NOT wish you to think that I meant changing to K & N filters mounted individually at the carburetor intakes, which creates special additional problems (besides doing LOUSY filtering).
Regarding the stock location of the air filters on your BMW Airhead Motorcycle:
When installing a K & N filter, there is NO advantage other than reducing the cost of buying filters, and even then, it will likely take YEARS before there is ANY cost savings.... but, ending up costing $$$ for engine damage.
K & N use does NOT require carburetor jetting changes if they are replacing the stock pleated paper filter in the stock place on such as BMW Airheads. When replacing the stock pleated paper filter For FUEL INJECTED bikes, such as the K series, the K & N does not upset the fuel system for several reasons, INCLUDING the engine being automatically adjusted by the fuel injection components, such as the oxygen sensor or mass-airflow sensor, etc. (depending on model/year). The air filter on a K bike is in a fairly decently protected area, same for the R bikes too.
The K & N filters have only two characteristics that make them POSSIBLY of value, and that is when the bike is ridden in racing or in off-road or other areas with a VERY HIGH LEVEL OF SILT & DIRT IN THE AIR....and you ARE willing to allow some abrasive dirt into the engine; AND by this I mean that conditions are such that need to clean the filter QUITE OFTEN, without replacement. The stock pleated paper filter, instead of lasting 25,000 to 50,000 miles, might only last a fraction of that, even with cleaning, in extreme dirty atmospheric situations....so, THEN, the cleanable K & N, ETC, COULD be useful, but keep in mind that the K & N filters will let abrasive dirt into the engine.
The K & N filter does a LOUSY job at filtering fine particles until it is quite dirty (yes, even with proper oiling of the K & N filter). NOTE that the stock BMW air filter will last a rather long time, many will go 30,000 miles OR MORE, in average conditions. Less if the atmosphere is relatively dirty from such as dust storms, etc. More if the air is cleaner. Just because the pleated paper stock filter looks a bit dirty does NOT mean it is not still filtering well! Contrary to information from paper filter manufacturer's, ETC., they OFTEN can be gently blown-through with compressed air, and they will run many more miles. As much as 60,000 miles has been safely done on BMW stock filters under excellent conditions. The BMW stock filters are quite oversize for the air amount used by the engine.
Many competitors with air cleaners from K & N will not use the K & N sticky red oil on them, and thus the K & N filters are being used to, essentially, filter LARGE particles only... and engine wear is greatly accelerated (filter oil helps SOME)! A partial fix for this filtering problem is to install a FOAM surround, or other type of additional filtering medium, be placed on top of or around the filter (depending on the type and mounting). This creates a slight pressure differential, defeating some of the K & N claims, but the outer foam can usually be washed and wrung-dry-enough. This is unlikely to be as good as pleated paper filters in actual filtering. The foam surround, even a thick cloth!, can be removed and washed; an advantage in quite dirty area racing. CONSIDER that racing engines are rebuilt often, more so if they have K & N filters and the racing is in quite dirty conditions.
The bottom-line, in case you do not wish to read further:
The K & N air filters, used as substitutes for the stock location, stock pleated paper filters, will, in my opinion, greatly accelerate engine wear; &, offer NO breathing advantage under normal paved road, nor most off-road conditions as described by me, for common use. The K & N filter can do a FAIR JOB of filtering; if coated, and more so if there is a proper foam surround over the filter. 'FAIR JOB' is not really good like the stock pleated paper filters!
The original article had the results of ISO 5011 testing of many types of air filters. The testing was independently performed under controlled conditions using a $285,000 machine at Testand Corp of Rhode Island (manufacturer of the machine). Arlen Spicer organized the test. Ken, an employee of Testand, offered to perform the tests at no charge. (These tests typically cost ~ $1700.00 per filter and MUCH MORE now-a-days). Ken shared Arlen’s interest in performing an accurate unbiased test of different types & brands of engine air filters. The filters used in the test were purchased retail & donated by Arlen & others. The detailed reports from the testing were compiled & originally were presented as part of this article you are reading.
ISO 5011 Test: The ISO 5011 Standard (formerly SAE J726) defines a precise filter test using precision measurements under controlled conditions. Temperature & humidity of the test dust and air used in the test are strictly monitored & controlled. As Arlen learned in attempting his own tests, there are many variables that can adversely affect filter test results. A small temperature change or a small change in humidity can cause the mass of a paper filter to change by several grams. To obtain an accurate measure of filter efficiency, it’s critical to know the EXACT amount of test dust being fed into the filter during the test. By following the ISO 5011 standard, a filter tested in Germany can be compared directly compared to another filter tested 5 years later in Rhode Island. The ISO 5011 filter test data for each filter was contained in two test reports; Capacity-Efficiency and Flow Restriction.
Flow Restriction: This report presented flow restriction of a clean filter resulting from an increasing airflow. The differential pressure restriction across the filter is reported in inches of water (IN H2O) versus Air Flow in cubic feet per minute CFM.
Filter Efficiency: Filter efficiency is a measure of the filters overall ability to capture dirt.
Accumulative Capacity: This is a measure of dirt holding/loading capacity before reaching the maximum restriction limit - Initial Restriction + 10 IN-H20.
Accumulative Gain: The total amount of dirt that passed through the filter during the test.
Initial Restriction: The Filter under test’s resistance to flow at 350 CFM.
Dirt Passed Versus Total Test Time: The graph showed each the duration of each filter’s test versus dirt passed (Accumulative Gain).
Dust Loading: The dust loading curves showed graphically how each filter responded to a constant 9.8 gms/min dust flow before reaching the maximum restriction limit.
(Arlen) SPICER wrote (September 2004):
"Now that I am not doing the tests & my objectivity is not necessary, let me explain my motivation. The reason I started this crusade was that I was seeing people spend a lot of money on aftermarket filters based on the word of a salesperson or based on the misleading, incomplete or outright deceiving information printed on boxes and in sales literature. Gentlemen and Ladies, Marketing and the lure of profit is VERY POWERFUL! It is amazing how many people believe that better airflow = more power! Unless you have modifications out the wazoo, a more porous filter will just dirty your oil!(dirt will DAMAGE your engine, not just dirty your oil.) Some will say " I have used aftermarket brand X for XXX # years with no problems. The PROBLEM is you spent a chunk of ching on a product that not only DID NOT increase your horsepower, but also let in a lot of dirt while doing it! Now how much is a lot? ANY MORE THAN NECESSARY is TOO MUCH!
Now I am not saying that ALL aftermarket filters are useless. A paper filter does not do well if directly wetted or muddy. It may collapse. This is why many off-road filters are foam. It is a compromise between filtering efficiency and protection from a collapsed filter. Now how many of our trucks collapse their filters from mud and water? However, if a filter is using "better airflow" as their marketing tool, remember this....Does it flow better? At very high airflow volumes, probably. BUT, ..... CAN'T flow that much air unless super-modified, so what is the point? The stock filter will flow MORE THAN ENOUGH AIR to give you ALL THE HORSEPOWER the engine has to give. And this remains true until the filter is dirty enough to trip the air filter life indicator. At that point performance will decline somewhat. Replace the filter and get on with it.
Hopefully the results of these tests will do 2 things. Shed some light on the misleading marketing claims of some aftermarket manufacturers and/or give us new insight on products already on the market that are superior to our OE filter. I stand for truth and will eat my words publicly if my statements prove wrong. I appreciate all of the help and support that you members have offered in this project. It would simply be impossible without your help.
A huge thanks to Ken at Testand for his willingness to take on this project. I would be spinning my wheels from here to eternity without his help... SPICER"
The full article was previously numbered 12B, but was somehow lost from the Technical Articles LIST Page LINK and LISTING, a long time ago. I recovered it, renamed it 12C, and made a new place for it on the articles list. I had continuing labor intensive problems maintaining this article, hence the 11/20/2013 changes:
11/20/2013: Completely revise and simplify. Keep much from some years ago, such as 2009. Remove all dead linking charts and databases. Remove all prior revision notes. In particular remove this link:
http://duramax-diesel.com/spicer/index.htm which no longer links directly to that article. Added at the top of my revised article is this:
http://forums.nicoclub.com/debunking-the-k-n-myth-why-oem-is-better-t180100.html which contains many of the more pertinent parts/charts of the original article.
12/24/2015: Update slightly, meta-code area for W3C. Check links too. Narrow the article to better accommodate small screens. Increase font size.
03/05/2016: Update meta-codes, layout, clean-up.
08/11/2016: Extensive update to metacodes, scripts, H.L. Update to modern HTML A/R. Minor other changes to layout. NO technical information changes.
© Copyright, 2014, R. Fleischer
Return to Technical Articles LIST Page
Return to the HomePageLast check/edit: Thursday, August 11, 2016