Many Land Rover turbo diesels were fitted with Catalytic Converters in the downpipe from the turbo. These act partly as a silencer but also cause a restriction to the flow of exhaust gasses from the turbo causing more “lag” or delay in the turbo creating maximum power. The honey-comb of the CAT can block up from years of use and the restriction reduces power and efficiency.
Removing the CAT will improve throttle response, power and reduce turbo lag. As the engine is breathing more efficiently most customers report an improvement in economy also.