VRSF Catted Downpipe BMW X3 X4 M40i B58 G01 G02 BrushedVRSF Catted Downpipe BMW X3 X4 M40i B58 G01 G02 (Brushed) The factory downpipe on the B58 X3 M40i and X4 M40i is a restriction that limits what these SUVs can do. The VRSF Catted Downpipe replaces it with a full 4. 5" SS304 stainless steel unit with a 200 cell high flow race cat, reducing back pressure and delivering 25 30 horsepower gains with a tune, while keeping a catalytic converter in place for street use. ModsDirect supplies this downpipe to