As you may know, Royal Purple is well known in racing circles. The chemistry they use is something AMSOIL, Inc. chooses not to use. One of their big selling points is extended drain intervals. Some additive chemicals can cause adverse conditions when used for long periods.
Royal Purple uses a different chemistry than most oils. They are one of only a handful of marketers using Molybdenum Disulfide (Moly) in their oil. Moly is a solid material, which is specifically banned by CumminsŪ, due to excessive valve train wear.
Moly is a processed mineral that is similar in appearance to graphite. Moly has good lubricating properties when used either by itself (in dry powder form or as an additive to oil or other lubricants). Particles of the Moly can come out of suspension and agglomerate. This can actually clog oil filters or oil lines and the rest normally settles in the bottom of the oil pan. This seems to be more likely when using extended drain intervals. In 2005, the test we ran on Royal Purple involved their 20W50 Racing oil versus our AMSOIL Series 2000 Synthetic 20W50 Racing Oil (TRO).