This is the lower downpipe that connects to your factory or any aftermarket exhaust that accepts factory gaskets. This piece is included with our N54 turbo kit but may be purchased to work with other brand turbo kits. Modifications may be needed to work with other brand turbo kits. The unit is made from 100% 304L stainless material. It starts as 3" v-band and enters a 3" stainless flex bellow (not cheap flex couplers that may restrict flow after use) which then splits to dual 2.5" tube. O2 sensor bungs are placed upright so your O2 sensors won't go bad.