All Supersprint alternate connecting pipes are mandrel bent for maximum performance. The alternate pipe is designed to replace a resonator that is standard in that same position. This option will increase sound slightly and reduce overall system cost. The polished pipes are manufactured from 100% 304 stainless steel, while the black pipes are aluminized mild steel. On the 540i Sedan and Touring models you will need to use 022 785 912, Supersprint Y Connecting Pipe.