The K&N website mentions filtration "as small as 10-20 microns in size." A Ford Taurus SHO website mentions "One other thing I learned is the media in a Mobil 1 filter only looks the same as a K&N oil filter media. The Mobil 1 filter has much higher synthetic fiber content designed to filter down to 10 micron while the K&N is designed for 'more sporting' applications and filters down to only 20 microns. The Mobil 1 is focused on deep cleaning while the K&N is optimized for higher flow." (This information appears to have been relayed to the SHO guys from a Champion, K&N, or Mobil 1 tech rep.) In comparison, Champion claims their $4 AC Duraguard filters have 25-30 micron capability.
The SHO website also mentions that both the Mobil 1 and K&N filters have shells 0.017 - 0.022 inches thick, but for some reason the K&N has a burst rate of 550 psi, versus 600 psi for Mobil 1. Some other shell thicknesses in inches (burst rates not known):
AC Duraguard: 0.015
AC Ultraguard: 0.0135 - 0.0180
Motorcraft: 0.0085 - 0.0150
Purolator PureOne: 0.009 - 0.011
STP: 0.012
Wix: 0.014
So it would indeed appear that the high-end filters have slightly thicker shells, although there's nothing uniquely robust about the K&N when compared to other $10 filters.
PureOne filtration specs:
-98% Multiple Pass Test (SAE J806)
-99.7% Single Pass Test
-BETA ratio of 7.2 at 10 microns
-Efficiency rating of 86.1% of 10 micron particles
Perhaps someone well-versed in BETA ratios and the like can interpret this for us. Here's a good pdf primer on micron ratings:
http://baldwinfilters.com/engineer/pdf/89-5r.pdf
Personally I've come to the conclusion that the "high filtration" filters (Mobil 1, PureOne, Wix T03 media, Fram X2, Baldwin HPG, Fleetguard StrataPore, etc.) all appear competitively marketed as "10 micron filters" (give or take), although they use various testing methods to get there. Therefore I suspect that other features (bypass valve construction and location, silicone drainback valve, etc.) might prove the best tiebreaker. In my opinion, the Wix and PureOne filters offer good bang-for-the-buck "10 micron" filtration for only six or seven bucks.
Paying homage to the flow-versus-filtration argument, I'll steal some words from "Commuter" at another message board (link below): "...I cut open a Purolator PureONE just this past summer and while it had more pleats than the typical filter, I did not find it 'packed'. There was still space between the pleats...One of the other important specs is flow vs pressure drop (or vice versa). It's easy to make a filter with great filtering capability, but it may be so restrictive that there will be a high pressure drop. Again, 'looking' at the media gives you no indication of this characteristic. The filter I use employs microglass fibers. It filters to much smaller particle sizes than most filters, however, it has a lower pressure drop per given flow rate than most filters. The two are not necessarily mutually exclusive."
http://pub110.ezboard.com/fultimatesubarumessageboardsfrm6.showMessage?topicID=98.topic
If you haven't read it, the SHO lube article is a great read, although unfortunately it's got no nudie pic's whatsoever:
http://www.shoclub.com/lubrication-oil/lubrication-oilpart1.htm
NOTES: Sources included the SHO article (info 3 yrs old), an update to same from July 2002, the Mini-Mopar filter site (a few years old?), and the K&N and Purolator websites.
[ October 25, 2003, 08:04 PM: Message edited by: TC ]