"ASME (mechanical engineering society) did a study years ago for diesel air
filters for earthmoving equipment.  They found the best is a folded treated
paper system FOLLOWED by an oil bath system (a la aircooled bugs) AND
regular maintenance.  They rated the filtration properties of the K&N oiled
foam type as poor.  They were not concerned with HP/MPG only with
preventative maintenance."

        Just a note here: In several of these posts like the one above, the
K&N has been referred to as "oiled foam". It is not an oiled foam type
element, and that is a signifigant detail.
 Filters such as the UNI-4 are foam, the K&N is cotton fabric layered between
steel mesh.   - Ed