Griffin,
Have you read this air filter test (as posted earlier in this thread)?
http://home.roadrunner.com/~jbplock/ISO5011/SPICER.htm
There are all kinds of tests showing how much dirt is being trapped, let though, pressure drop, etc. I'm not sure if it answers your questions, but there is lots of good information.
Bottom, K&N's let more dirt though. Is this extra dirt going to wear out your engine sooner, and if so, how much sooner? I don't know. Personally though, I'm not inclined to take chances.
I didn't see that earlier. Thanks, it provides some data that, although for a different application, can probably be used for some rough comaparison evaluation.
The test was performed on diesel engine filters, and used different brands with essentially three different styles:
Foam (Uni)
Packed Fiber (K&N)
Paper (various brands)
As for my first question, the filtration rating, the test didn't completely answer it, but did provide usable data. The dust media is described as ranging in size from "under 2.5 microns" to "greater than 80 microns". I don't particularly like that description, because it doesn't really tell us anything. A hydrogen atom is "less than 2.5 microns", and a red giant star is "greater than 80 microns". So we can't get a true rating for each filter, which would read in this format:
Rated 99.6% entrapment down to 1 micron at rated flow.
Rated flow 80 scfm @10" H2O - 24" H2O
That rating means that a filter will capture 99.6% (by mass) of all test media passing through it that is larger than 1 micron, with initial (clean) pressure drop of 10" H2O and saturated (dirty) pressure drop of 24" H2O, passing no more than 80 standard cubic feet per minute of air. The filter will capture some particles below 1 micron, perhaps a lot, but it hasn't been tested with smaller media.
Anyway, the testing pretty much confirms that the K&N has the least pressure loss, but allows more dirt through than paper. Interesting to note that the foam type of filter (in this case, Uni brand) allowed about the same amount of dirt through as the K&N, and had a higher pressure drop (about in the middle of the paper elements).
So...what does it mean for your engine?
Probably not a whole lot as far as wear and tear, your oil filter will catch the dirt. Remember, Suzuki used foam elements on several GS models, and it appears to filter about on par with a packed fiber element. Evidently Suzuki decided it filtered well enough. Your oil filter will not last as long, but I think that we tend to change our oil filters (every 1,500-2,000 miles seems to be the norm here) long before it is necessary anyway, at least in general street riding.
To each his own. I prefer the increased rideability that is afforded with packed fiber filters, and have a track record of engine durability to not worry about the increased dirt loading on the oil filter.
If using the finest (and in this case, I'm referring to particle size) filter to eliminate as many particles as possible from entering your engine at the possible expense of rideability is the most important aspect to you, then use the paper.
On my GS700, the original Suzuki element is oiled foam. With stock jetting, it flowed too much air, particularly at low rpms. With a Stage I kit, it didn't flow enough air at mid and high rpms, hence the switch to the K&N.
The Stage I kit changes the bike from a wheezy, cold blooded beast that took five minutes to warm up on cold mornings (even when brand new), to an instantly fired-up charger that was ready to go in less than a minute. To me, that change is well worth the reduced filtration level. I wish I'd done it twenty years earlier.
And by the way, yes, one aspect of my job is evaluating, sizing, spec'ing, and applying filters in industrial applications.