B58 Downpipes 3-Series 4-series GR SupraLAB B58 Downpipes Unleash the true performance of your B58 engine with our LAB B58 Downpipes. Designed for maximum power gains and faster turbo spool, these downpipes eliminate the restrictive stock catalytic converters, dramatically improving exhaust flow and throttle response. Our precision engineered flex section minimizes stress and vibration to protect both your turbo system and chassis under high load conditions. Important: These downpipes are