RE: Air Filters

["Fadeev, Alex" <Alex.Fadeev@xxxxxxx>]

"Thomas Petersen" <bmw318is92@domain.elided> wrote:
> 
> Your thougths about the effiency of the filtering is questionable,
> I find it very hard to beleave that the filter effiency on the K&N
> is poorer than that of the original! So, that should *not* be the 
> reason for not installing the filter..

Dear Thomas, finding something hard to believe does not, in and of itself,
disprove a fact or a claim. You need data to support your position. In this
case data is on the side of Rob Workman's suspicions. Read this reply on the
subject that Jim C's posted (and I saved) a while back:

<start quote>
> I was curious if the K&N filter inserts work as well as the stock air
filter.

  No, they do not.

  Testing, both by a filter lab in the United States, and by a filter 
  lab in the UK under the auspices of the Motor Industry Research
Association
  (aka MIRA.. sort of like our SEMA) have shown that they do not.

  The raw results from the US Lab (for the doubting thomases) are posted at:

  http://www.bonnevillemotorwerks.com/dynocharts/intake/KN/kntest.pdf

  This is in Adobe Acrobat PDF format.. you'll need the Acrobat Reader
  which is of course available from http://www.adobe.com if you don't
  already have it.  It's free.

  What the results show is that:

  1) The Cotton-Gauze filters let in considerably more dirt (300-500% more)
     than stock 
   
     and

  2) Very rapidly, the cotton-gauze filters load up and flow WORSE than
stock

     Where a K&N type filter flows rather well right out of the box, it
cannot
     sustain that flow for very long at all.

  As soon as I get "reprint/excerpt" permission from MIRA I will post some
  information from their tests.

  Jim Conforti  

</start quote>


> Another more important issue, is the intake air temperature. If 
> you equip your engine with the cone-type K&N, you should do 
> something to isolate it from the rest of engine compartment.

very true.
unshielded cone filters (K&N or any other) were reported to yield a net
_loss_ hp.

> Regards,
> Thomas Petersen,
> '92 318iS Coupe - Supercharged to 205HP (with K&N :-))
> 
> >Date: Thu, 25 May 2000 23:56:39 EDT
> >From: GRobWorkII@domain.elided
> >Subject: Re: Air Filters
> >
> >Paliava,
> >
> >   Beware the savvy marketing of aftermarket air filter 
> >manufacturers...  
> >At the risk of opening a "digestive can of worms" here, let's
> >just say that there are many halfway respectable dyno comparisons
> >showing negligible (0-2 hp) increases that accompany the use of 
> >filters such as the K&N... The stock airbox on your M30 is VERY
> >nonrestrictive, and provides a valuable service that some of the
> >aftermarket filters seem to overlook - it actually keeps foreign
> >particulate from entering the intake. To illustrate;  I let my 
> >last paper filter go for 24k miles.  The incoming air side of
> >the filter and airbox were quite nasty, caked with a layer of
> >fine silts and dust... (There is an obvious need for filtration
> >of incoming air.)  The intake side of the filter and airbox were
> >perfectly spotless.  Would a K&N have filtered the air the same?
> >Questionable...  Is that chance worth 0-2 hp?  Not for me.  
> >Keep in mind that as an oiled foam filter gets caked with filth, 
> >restriction drastically increases.  I'd put my money elsewhere!
> >
> >Rob Workman
> >'85 535i (Holga)

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