No subject

Thu Nov 20 11:46:45 EST 2003

```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

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.

-----Original Message-----
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of tblack
Sent: March 3, 2003 3:51 PM
To: jimk at spotgraphicsinc.com; Randy Reimer
Cc: serge411 at speakeasy.org; s-car-list at audifans.com
Subject: Re: [s-cars] Re: MAF foul up

One of the car mags did a comparo of after market filters vs OEM and
concluded that the OEM were as good as, if not better than, the after-market
ones. In fact I recall that the filtering of dust was significantly worse
with the non - OEM replacements. I personally would not use any other than
the OEMs.
My \$0.02
Tom Black.

> If there are quantifiable
> results, please post 'em.  There's no real difference in the seat of the
> pants analysis, does the dyno tell otherwise?
>
> - I've never seen any, and based on my experience, would probably never
again
> buy a non-stock type filter for an otherwise normal street car no matter
what
> a dyno shows.
>
> Jim
>
>
>
> _______________________________________________
> S-CAR-List mailing list
> S-CAR-List at audifans.com
> http://www.audifans.com/mailman/listinfo/s-car-list

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