No subject

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.

>I have heard the same things about these filters, not sure if it is true
but my car 
>does not have a MAF and I have never seen any dirt or oil on the "other"
side of my
>K&N. 
>
>Mike Guidotti