B48 Catted Downpipe: Complete Guide The BMW B48 engine is modern and efficient. However, the factory exhaust limits airflow. A B48 catted downpipe improves exhaust flow while keeping emissions control. This upgrade is popular among daily drivers. It offers power gains with balanced sound and reliability. What Is a B48 Catted Downpipe? A downpipe connects the turbo to the exhaust system. It...