Active Autowerke Signature Equal Length Mid-Pipe - F97 X3M | F98 X4MThis exhaust system upgrade was designed and engineered to work with most after market exhaust systems mufflers on the market today with only a single cut needed in each side of the stock mid pipe. It is a bolt on that can be performed by most and the stock mid pipe can also be reinstated if needed. This system provides the maximum flow available and restores the sports car growl expected from a BMW M Series car. Active Autowerke is able to improve on