BMW B58 Downpipe: Complete Guide The BMW B58 engine is powerful and efficient. However, the factory downpipe limits exhaust flow. A BMW B58 downpipe upgrade removes this restriction. It improves power, sound, and turbo response. This guide explains everything clearly. It is easy to read and understand. What Is a BMW B58 Downpipe? A downpipe connects the turbo to the exhaust system. It controls...