No subject

TEST
filter and is then captured on the analysis membrane we can calculate
the
efficiency of the TEST filter in Question.

First, the filters:

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
thru a total of 6.6 grams of dust in.  If we used the new K&N filter we
get
14.8 grams of dust.  Thats 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.


From: "John Larson" <j.d.larson at verizon.net>

>This has been a topic a number of times before.  Last time around we
saw the
>topic we had a post regarding the area of filter material.  K&N filters
>better per square inch (with the proper oiling) but has FAR fewer
square
>inches of filter area, and the particle size allowed by is somewhat
larger.
>There is a website somewhere out there from a mining company
maintenance guy
>that talks about  drastically accelerated wear and decreased overhaul
>intervals of heavy mining vehicles after switching the fleet to K&N.
Mega
>dollars later, the filtration was changed back to the OE style,
whatever
>that was.  I think the HP clams made by listers are exaggerated and,
for the
>most part, totally unverified.  Consesus is they sound more powerful,
>though.  John

From: "Nate Stuart" <newt at newtsplace.com>

> > I think that all are completely adequate.  The only reason I like
the
K&N
> is
> > because it truly IS reusable.
> >
> > That said, the size of the particles allowed to pass in either
situation
> is
> > ridiculously small.  In my opinion, any air filter will be
sufficient if
> > properly replaced/cleaned.  The goal of the filter is to keep out
objects
> > that would damage the engine, and I can't see ANY particle that
would
pass
> > through these filters causing any damage.  Please let me know what
> > intake/engine component could be damaged by something that small.
It's
> not
> > like the air has to pass through a tiny opening like the fuel
injectors.
> >
> > -Ryan