VRSF Catted Downpipe BMW M240i 340i 440i 540i B58 Heat ShieldVRSF Catted Downpipe BMW M240i 340i 440i 540i B58 Heat Shield The factory downpipe on the B58 is a restriction that limits what these engines 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 and heat shield, 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