not strictly landrover talk but my L200 has been running a k+n induction kit for the last 3 years and the engines still running sweet as a nut, sails the emmisions every year and thats without a cat, before owning this i had a pajero with k+n also and no probs and before this i went through the whole boy racer stage for several years so every car got treated to a performance filter, whether it be k+n/pipercross/green and it never did any harm to my engines, way i see it is if they are cleaned regularly and thoroughly then theres no problems with them.