Ian,
So is your opinion that this type of filter ok or not ?
It is a cotton/mesh/oil impregnated type. Seems good in principle, moist
oil should trap dust. I don’t live in a dusty area, and 80% of my mileage
is highway. The filter I got ‘looks’ to have very much less filter element,
thus less surface area, and maybe less filter efficiency ???
I’m aware of principles of pressure drop flow rates etc, but things get
funny once you reach critical flow rate. I have no idea if a
cellulose/paper filter ever reaches critical, so I am confused as to the
comparison. One individual on the list made a comparison to the filter
being a ‘boulder trap’ but they are running at 5000+ rpm and racing. I’m
looking at everday driving at no more than 3000 rpm on average, a few bursts
of speed are insignificant.
I’ve worked around filters before in other industry and know about the
micron size/capture principle. IMO, the best way to make a comparison is to
get an idea of the pressure drop at ‘normal’ driving speeds through both
filters. K&N boasts (and one cannot be sure of manufacturers claims) good
filtration rates across a wide range of micron sizes. In my rough
perspective of understanding particle size, 5.5 micron (the lowest on the
list) is fine.
Back in my days of industrial pollution testing, we were concerned with
primarily micron sizes below 10 microns, the typical industrial effluent
size. But… where dose one factor that in ??
My conclusion is… I live in a fairly industrialized area, a lot of big
industry around, coal fired power plants, various industries belching their
pollutants. Particulate, NOx, SO2, and who knows what else. Most of the
particulate in my region is not the large stuff, so according to K&N’s
charts, they claim a pretty good efficiency.
I don’t feel too bad about using the filter, but am persuaded to delve back
a little further into my environmental engineering days to get a
quantitative look. Each region presents itself with different particulate
sizes, and I am far from racing my car.
Dave----- Original Message -----
From: “Ian and Kathryn” ianandkathryn@optusnet.com.au
To: “Dr. Gregory Andrachuk” v12-vdp@shaw.ca; “‘1985vdp’”
<@1985vdp>; xj@jag-lovers.org
Sent: Tuesday, January 24, 2006 5:13 AM
Subject: RE: [xj] K & N Air Filters
I might be able to offer a helpful comment on this one.
Filters as used for air, fuel, and oil use a ‘depth capture’ mechanism -
like a sponge. As such it isn’t helpful to think of them as a strainer,
where everything above the mesh size gets caught, and everything smaller
gets through.
When assessing a filter the type/quality of the ‘media’, its surface area,
and the fluid velocity determines the % of particles that get through of
any
given size. So for a cellulose (paper) element you may find that at low
engine power levels 99% of 10um particles are trapped, whereas at high
speeds only 90% get trapped. If the element is heavily restricted the
effective surface area is reduced, and so the particles tend to extrude
through more readily, while at the same time seeing a higher pressure drop
across the element.
The benefit of using a quality element is that the pressure drop is lower,
hence the air downstream is denser resulting in greater potential power.
The
reduced pressure drop is due to a combination of superior media (e.g.
micro
glass fibres), and greater surface area, so the effectiveness of capture
will likely be better not worse.
In hydraulic systems we often install grossly oversized filters - the
system
stays medically clean, the filters never need changing, and the rest of
the
system receives better protection. Filters cost more, however.
When I fist bought my S1 14 years ago, it would go through fuel filters
every 3-6 months. SO I tossed out the pathetic little cotton thimble
beasty
in the boot, and installed a hydraulic standard filter with at least 10
times the area. I think I have changed it once since - because I thought I
should rather than because it needed it.
An item of total trivia that may amuse some of you is how hydraulic
filters
are tested for affectiveness according to an international standard. A
special dust is mixed with fluid and passed through the filter under
controlled conditions and measurement. The dust comes from a special part
of
the desert in Arizona, becuase the particle size distribution perfectly
suits the test…
Regards
Ian Duncan, Wollongong Australia.
'71 S1XJ6 with 350&T400.
'77 XJC6 being restored.
-----Original Message-----
From: owner-xj@jag-lovers.org [mailto:owner-xj@jag-lovers.org]On Behalf
Of Dr. Gregory Andrachuk
Sent: Tuesday, 24 January 2006 1:34 PM
To: ‘1985vdp’; xj@jag-lovers.org
Subject: RE: [xj] K & N Air Filters
I have just one question about K&N filters: if more air gets through,
logic suggests that more dirt gets through, no?
Gregory
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