After many years of designing and testing racing oil systems and related components, we've determined what's most important to oil filtration. Many filter manufacturers stress the importance of filtering the smallest particles out of your engine's oil, with references to "micron ratings" of 10 or less for a filters efficiency.
With the help of research performed by filtration technology experts, Moroso engineers have determined that particles smaller than 20 microns in diameter are not large enough to produce engine wear. Furthermore, we've found that filters with extremely low micron ratings create an excessive pressure drop across the filter. They can be so restrictive that the filter by-pass valve can open. With the by-pass valve open, unknown to you NO FILTRATION will occur!
To maximise filter performance, Moroso Racing Oil Filters have a rating of 27 microns, which produces a maximum initial restriction of only 2.5 psi when tested to SAE j806! The result is less pressure drop, more flow, less oil by-pass and maximum filtration performance important in severe racing conditions.
Cross Reference: Fram PH30, Wix 51069, K&N HP-2002