Bagged an '03 STR. High miles but strong running. Quartz with Dove interior (which I like because of uniformity of color with door cards etc.) Plenty of fiddley stuff to occupy my time with ... but I've got a question. Has anyone banged out the honeycomb cat material, installed an O2 adap/extndr and had any successful results, or an opinion on this? I live in the sticks so I don't care about passing emissions or MOT. Will it fool the CEL? Will it bugger any other ECU perimeters. If not, I'd compound my sins by installing a flow through muffler (Thrush, Walker etc) at back end as well (I like the rumble of a V8). Will I expect low end torque loss? Droning? Any other negative results? I know the engineers spent a lot of time here but they were worrying about pleasing the "gents" commuting to work.

 

Fooling the downstream O2 sensors cause more problems than they solve, the downstream sensors are also used for fuel trims. If you put extensions or mincats on the downstream sensors your fuelling will be off.

Have a look here https://www.jaguarforums.com/forum/x...-remap-140980/ , you can see the dyno chart with the big lean patch in the AFR's, on that car we removed the minicats, changed the emissions settings, and it was all fixed. No more CEL, no codes, and the fuelling was correct.

There is a way to disable the catalyst efficiency monitoring so that you don't get a CEL or the P0420/P0430 codes, I know a guy in Phoenix who has the diagnostic tool which can do this properly.

A properly designed exhaust, not oversized i.e. stick to the 2.25" size, with an x-pipe, and some properly designed mufflers will be loud enough without compromising back pressure. If you want the old-school V8 sound then fit an H-pipe crossover instead of an x-pipe.