A quick search gave me this about the rating of meeting only 50% of it rated value:
http://www.carjunky.com/news/motor_oil/mom7.shtml
Quote:
IF MICRON LEVELS ARE TO BE USED
Nevertheless, you may still want to compare filters using micron ratings. If this is the case, the following is a good rule of thumb. A filter is considered nominally efficient at a certain micron level if it can remove 50 percent of particles that size. In other words, a filter that will consistently remove 50% of particles 20 microns or larger is nominally efficient at 20 microns.
A filter is considered to achieve absolute filtration efficiency at a certain micron level if it can remove 98.7% of particles that size. So, if a filter can remove 98.7% of particles 20 microns or larger, it achieves absolute efficiency at that micron level.
Most off-the-shelf filters are based upon a cellulose fiber filtration media. Most of these filters are, at best, nominally efficient at 15 to 20 microns. They won't generally achieve absolute efficiency until particle sizes reach 30 microns or higher.
High efficiency oil filters have filtration media made of a combination of at least two of the following: glass, synthetic fibers and cellulose fibers. Those that use all three are generally the best in terms of filtration. Those that use only two will fall somewhere in between. The best of these high efficiency filters will achieve absolute efficiency down to about 10 microns and will be nominally efficient down to 5 microns or so.
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Well the K&N guy stated
Quote:
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Our synthetic-cellulose blend filter media stops particles as small as 10-20 microns at 90 Percent efficiency while still allowing high flow rates (between 12-16 gallons per minute, depending on filter size).
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So wouldn't that mean that their best filter can pass things as large as 22 microns.
Further I don't believe thier GPM. That is going to be the best filter size which will be MANY MANY times bigger than our little filters and at what PSI input from the oil pump... 40psi?
I thought I read that the K&P filter has absolute (100%) efficiency at 35 microns. NOTHING gets past it bigger than 35 microns.