In Reply to: Re: Plse tell me why b4 I mod mine! posted by Joe S. on July 31, 2001 at 22:28:13:
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.
Steve Dinan's view on K&N:
1. The K&N filter is not as effective in taking particulates out as the factory paper filter is, so you will increase engine wear.
2. The factory filter pulls cool air from outside the engine compartment, while the K&N will pull warm air from the area behind the radiator. Warm air is less dense than
cold, so this can cost 6-13 HP!!
3. According to their actual tests on a Dynamometer, you will *lose* horsepower, not gain it.