S58 BMW G8X G80/G82 M3 & M4 DOWNPIPE INTEGRATED O2 SPACERSDescription Stainless down pipes for the S58 G8x M3 and M4. Tested and used in our own G80 M3 development car. More real exhaust sound and improved flow. If you're only going to make one exhaust modification, this should be the one. We have integrated a mini cat inside the downpipe to keep them free flow and take the place of an external O2 sim. Inside each downpipe is an O2 mini catalyst spacer. To Eliminate absolutely ALL CEL's due to catalyst