Having owned a K&N air filter for quite a while, I had never seen any improvement in performance with pervious models - both + Bluefin. So had given up fitting it and stuck with standard paper ones, just considered it £40 wasted and almost Ebayed it.

Anyway just out of interest I put it in the SD4 with Bluefin installed. Now it has made a noticeable difference to the increase in performance and that was versus a new paper element as it had recently had a service. Performance is definitely sharper with the K&N fitted especially at higher rpm / road speeds.

I guess its a case of the air flow becoming the limiting factor as other factors controlling performance have been improved upon = TD4 - SD4 and standard to Bluefin.

A K&N filter made a massive difference to my 1st Freelander 1 powered with the Rover Diesel engine and a Jeremy Fearne chip installed and small air filter box. However it made no difference to a Chipped TD4 Freelander 1. And that was a pain to change but the filter was quite big, hence not a limiting factor. 1998 Feelander XDI Hardback - Gone
2002 Freelander TD4 GS Hardback - Gone
2004 Freelander TD4 HSE Stationwaggon - Gone
2007 Freelander 2 TD4 XS manual - Gone
2010 Freelander 2 TD4 GS Auto - Gone
2013 SD4 GS arrived April 2013