Remus BMW M3/M4 Racing Secondary Cat Replacement Tube (G80/G81/G82/G83)Remus Exhaust secondary cat replacement tube for the BMW G80 G81 M3 and G82 G83 M4. This set of tubes replaces the vehicle's secondary catalytic converters, improving the flow of exhaust gases which allows for a better sound and higher tuning potential. Usually, these secondary cat delete pipes would only be available as part of a full racing exhaust system so we're very glad to offer them individually as they make a great stand alone exhaust