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So what do you guys think about this?
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From: Don Herrero <don@sechq<img src=/i/dc.gif border=0 width=35 height=15>>
To: "'GLX'" <jettaglx@igtc<img src=/i/dc.gif border=0 width=35 height=15>>, "'GTi'" <email@example.com<img src=/i/dc.gif border=0 width=35 height=15>>
Subject: K&N debate
Date: Mon, 25 May 1998 09:58:54 -0500
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Reply-To: jettaglx@igtc<img src=/i/dc.gif border=0 width=35 height=15>
i got this off the Rover list. the guy that wrote it is (i think) a writer for one of the off road magazines.
Those of you who are regulars to the list may remember some fairly
heated debates over the effectiveness of K&N oiled cotton gauze air
filters. In general, we didn't argue over these filters being able to
produce a performance increase (especially in light of some good dyno
tests) but the bone of contention was the ability of these filters to catch
dirt. I had some tests that showed the K&N at least the equal of a paper
filter and talked about an upcoming independant test that would help clear
the air. Pun intended! I have been very busy of late but belatedly here are
the results of those tests.
The tests were done to compare a K&N filter against an AC paper
element (which had an added foam prefilter) and an Amsoil 2 stage oiled
foam filter. An enclosed fan assembly was used that had an airflow rating
of 540 cfm. At that flow, four ounces of dust was introduced to the filter.
This dust had been prepared via geological pulverizing and grain sorting
equipment at the University of Montana to contain 1 ounce of material
larger than .0049" but smaller than .0082" and 3/4 ounce of material larger
than .0082" but smaller than .0098". The remainder was smaller than .0049"
and some was into the "flour" category. Ceramic tiles were placed in the
airflow on the clean side of the filter that had been coated with a tacky
substance to catch dirt.
When the dust cleared, the K&N tile showed the most dirt, with the
AC paper filter only very slightly better. The Amsoil filter was very much
cleaner than either of the other two. Hmmm!
Incidentally, all three filters were tested while clean for
restriction at 540 cfm and there was a negligable difference between them.
The engine for which they are intended needs only about 400cfm, so there
would be no noticable performance lost from one to the other in theory. I
had flow tested a Fram fitler of the same size as well as a K&N and while
the latter flowed about 50% more than the former, the former flowed 40%
more than the engine needed.
There you have the facts. You can review them yourself at
http://www.bitterroot.net/diesel/diesel.htm, which is a very nicely done page
for GM 6.2 and 6.5L engines. Having spent many hours in discussion with Jim
Bigley, the person who did the tests, I am comfortable with the results.
Now my brief comments and interpretation.
1) This test seems to verify data I have that paper and oiled cotton gauze
filters are about even in terms of filtering ability. The AC had an added
advantage having a foam prefilter.
2) Question? What is an acceptable amount of dirt to pass though a filter?
All filters pass some and since there are engineering standards for this by
the OEMs, then we can surmise that at least the AC filter (an OE
manufacturer) would have passed this standard.
3) I would have liked to have seen how much restriction resulted from the
four ounces of dirt on each of the three filters. If the Amzoil filter had
completely plugged up with four ounces of dirt, for example, and the others
did not, of what use is the great filtering ability if the engine quits. I
do not think this is the case here, but you catch my drift.
4) My conclusion from this is that unless there is a big performance loss
for a particular filter, go with the one that filters best. The restriction
tests done concurrently (with a homemade manometer) showed that a large
enough filter of any construction had enough airflow to supply this engine.
The same would apply to any other engine. It's obvious by the tests I have
done that a K&N will outflow any filter of similar size by leaps and bounds
but if your engine needs X cfm and the filter you use exceeds that by 30%
or so (to accound for dirt buildup), you will not have any performance loss
whatever filter media you use. You could answer this question for yourself
on any vehicle this by calculating your engine's needs and then flow
testing the filter. This could also be tested on the vehicle with a
homemade manomete. .
5) For my part, I'm going to look into the Amsoil filters. Regardlesss of
my liking for K&Ns and the fact that they works as advertised, The Amsoil
filter was the clear winner in this test.