The use of quad tips also presented some additional challenges and fostered some innovation to the already visually impressive system constructed entirely of TIG welded and brushed T304 stainless steel. Confined to dual tips, the factory system utilizes only one exhaust valve and functions by eliminating the passenger side tip when the valve is closed, siphoning all gases through the muffler and out the driver's side tip for quieter operation. With the introduction of more pipes/tips, this methodology was not practical, or desired. In true Dinan M exhaust fashion, our talented engineering team decided that integrating a second valve to the system would garner the most favorable results in both symmetry and overall sound. The result is a system that incorporates larger 76mm tubing (vs 70mm stock) and allows freer flow through the entirety of the system but specifically to both outer pipes when the enlarged valves are open. The resulting flow and sound mimics an awe-inspiring straight pipe solution with a deeper and meatier tone, a defining element of all Dinan exhausts. In contradiction to the aggressiveness resulting from open valves, when the valves are closed, all gasses are forced into the muffler for sound deadening and exit the two inner tips. Regardless of valve position, the intimate nature of the interior is retained so conversation can continue without an excessively loud drone courtesy of numerous drone abatement technologies in the can. With the Dinan exhaust equipped on the M340i/M440i you get the best of both worlds, aggressive tone/sound and civility. A combination that is a paramount to any M exhaust, and now by virtue of tip count, the M340i and M440i. Welcome to the illustrious family.