I had failed original cats in two of my 318's, a ti(180k mi) and an ic(160k mi). Failed SMOG checks in both cars as a gross polluter. Swapped out both cats with Magnaflow 36004, which is CARB compliant/required here in California. Both cars passed the SMOG test cleanly afterwards. First install was just under $215, second one was $180.
I look for the cats to pass two inspections which are two years apart. If they last longer, great!
Good luck!
