Something of interest from the Corvette group - for the uninformed, Hib Halverson is VERY well known as a GM and vette representative...
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>From Hib Halverson, finspeed@aol.com
Hi VetteNetters, Back in Dec. and Nov. there was quite a bit of discussion of the K&N Filter. At the center of the controversy were questions about the K&Ns filtering ability ie: though its performance enhancing features are not in doubt, people wondered how good a filter it is.
The discussion got even a bit heated with someone on the anti-K&N side coming out and saying that the K&N pretty much sucks as a filter and is not good for your engine.
The only post I saw, pro or con, that backed up statements with test data was a post that cited a 1992 British Motor Industry Research Association dust filtration efficiency test of the K&N air filter. While this test was discussed previously, there are some things in it that need review.
The test procedure was done according to ISO standard 5011, an international standard for air filters of the type used on heavy-duty and commercial vehicles.
The filter was a K&N commercial type unit using K&N's oil-impregnated, gauze media and measuring 16. 14in. long and 10. 43in. in diamter. Air flow was 550 cubic feet a minute. The filter test "dust" was "coarse grade" dust as specified by standards used by ACDelco in testing their filters. Coarse grade dust is made up the following percentages of varying diameters of dust particles.
0-5 microns 12%
5-10 microns 12%
10-20 microns 14%
20-40 microns 23%
40-80 microns 30%
80-200 microns 9%
The starting pressure differential across the filter was 26. 45 inches of water. The test was run until the pressure differential reached 31. 49 inches of water then the amount of dust trapped by the filter was determined and compared to the total amount of dust introduced to the filter. Dust introduced was 5. 1680 lbs. and the dust trapped was 5. 1307lbs. It took 102min. for the filter to reach the 31. 49in. of water level. Filtration efficiency was 99. 28%.
Now, I have to qualify this test a bit to put it in the proper relation to a street high performance engine in a Corvette. First of all K&N commmercial filters typically are four-layers and units typically sold for use in passenger cars are three-layers. K&N has told me that the efficiency of the three-layer filter is 97% and additional tests back that up.
Next, the K&N commercial filter tested, had more filter area that the typical air filter we see in a high-performance V8 application, such as a 3x14in. unit. However, the efficiency of the filter media would be about the same. Only the time to reach a specified restriction level would change. It would be less because, for a given type of dust and a given flow rate, the smaller the filter was, the faster it would plug up.
Lastly, virtually no Corvette engine, run in a street high-performance duty cycle is going to see coarse grade dust in any significant amount unless the car is used as a farm or construction impliment.
Another test that's been done with K&Ns was in 1983. Again, it was done by the British MIRA but this test was done according to the SAE J726 standard which is a bit more familiar in this country. This test was done with AC fine grade dust, the composition of which is different and perhaps more typical of "dust" a street engine would encounter.
0-5 microns 39%
5-10 microns 18%
10-20 microns 16%
20-40 microns 18%
40-80 microns 9%
The test was done with a K&N for a motorcycle application which is a three-layer filter. The initial pressure differential was . 825in. of water and the ending differential was 6. 85. The airflow rate was 40 cfm. The dust introduced was 15. 6 grams and the dust trapped was 15. 1 grams. The efficiency of the three-layer filter was 96. 8, fairly close to the 97% K&N claims for its street high-performance automotive filters.
While the motorcycle filter is obviously much smaller than a V8 unit, the efficiency would be about the same. With a bigger filter, the time to reach the ending level of restriciton would be longer.
In yet a third MIRA test done with filters of a size typical of V6 engines in high-performance sports coupes, two K&N oval filters were tested. One was a 2. 56x7. 48x6. 18in. and the other was 3. 22x7. 05x4. 5in. The test was run to ISO 5011 and AC fine grade dust was used. The filters' efficiency levels were 97. 5% and 97. 6% respectively.
In my opinion these tests show convincingly that the K&N, oil-impregnated, gauze air filter is not only capible of low restricion but high filtration levels. All of the tests discussed here showed efficiency levels above that of the 95% which most OEs specifiy.
Many off-road racers must agree, because a lot use the K&N and, if the K&N works in that kind of enviornment and those off-road race engines are reliable, it must be a heck of a good filter.
In the U. S. Chrysler markets factory-approved performance kits for some of its truck engines. The kit includes a K&N filter and the kit's use is covered under the factory warranty. Chrysler would not offer a kit such as that if the K&N Filter could not meet OE filter efficiency goals.
In Japan Nissan markets similar factory-approved performance kits for a couple of models that are offered only in the Japanese domestic markets. Like the Chrysler, kits, the Nissan kits include K&N filters.
Also, the one way a K&N can fail as an air filter is if it is run, contrary to the manufacturer's instrictions, without being oiled. Another way it can fail is if it is run with the wrong kind of oil. If you use a K&N, best results comes from cleaning annually and reoiling every six months. If you operate your Corvette in a dusty environment (the coarse dust) clean and reoil more frequently. When you reoil, use only K&N's filter oil. Foam filter oil, engine oil, WD40 or ATF are not the proper products with which to reoil a K&N and will significatnly degrade the filter's efficiency.
cYa
H. Halverson
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Early '91 250, 727 AT, 307 rear... Banks Stinger exhaust, intercooler... US Gear OD... MORE than a match for every new PS Ford encountered so far...
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