With 200k miles you might want to consider replacing your cat, but don't get rid of it. I just had a custom, 3 inch, cat-back exhaust fabricated for my euro 500 SEL and, evidently, the increased flow accelerated the demise of my cats (190k miles). I had the cats replaced with new, free-flow cats and the power delivery became smoother (better low-end torqe) while the engine still breathes just fine at the top end. The sound is pretty mellow and they aren't expensive unless you go to the dealer for one.

New generation cats do not rob performance and help keep the air clean...it's a worthwhile thing to do.

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Richard Detoy
'84 300SD
'76 Moto Guzzi 850 Le Mans