K&N filters bad?

[David]

he following information was taken from a posting by Jim Conforti (AKA the Land Shark). Jim is a well known tuner in BMW circles. His web site is the Bonneville Motor Werks. The testing was done on a BMW air filter but the concepts should apply to all manufacturers.

Comparing Stock to Performance Air Filters

First, a "prologue". This was a scientific test, not one done by filter manufacturer X to show that their filters are better than manufacturer Y. The test results are pretty irrefutable as the test lab tests and designs filters where "screw ups" are absolutely NOT allowable (I can't say any more for security. Think "Glow in the Dark").

OK, with that in mind, onward.

A scientific test was done on TEST filters where air was loaded with ACCTD (some standardized "test dust" called AC Coarse Test Dust) and sucked through the TEST filter then through an analysis membrane.

>From the Quantity of dust injected and the amount that gets thru the 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.

Dave
87.5 CGT
SE Virginia
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From: FFGREG32 at aol.com
Date: 2004/03/10 Wed PM 09:41:15 EST
To: quattro at audifans.com
Subject: K&N filters bad?

I have been informed that K&N filters are bad for my car. I would like to see 
the data on this before I install this filter in my car. I will stay with 
factory filters if the data indicates that K&N filters could allow damage. I had 
never heard any of this before. If anyone could point me to any technical data 
or past discussions where this is indicated, I will be open to learning about 
it. If this is true that it causes damage to our Audis, then K&N needs to be 
upfront about it, or at least hear from those whose cars have been damaged. 
Anyone else have input on K&N? Thanks Greg
1989 200TQ
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