Getting back to the purpose of the thread and away from opinionated comments, where do K&N and Royal Purple fit into the oil filter mix in terms of quality?
I know AK bought K&N and a few others like that particular brand, but I was leaning more toward buying Amsoil or Royal Purple. To me, both look like quality filters, but I'm no expert.
Also, I can't find Royal Purple's API group number anywhere. I've heard that it's in group IV, but I've also heard it's in group V. However, I also read that Group V oils are reserved for air compressors and similar motors because they're not compatible with petroleum-based fuels and can actually damage auto engines.
