RRP downpipes are hand crafted from mandrel bent SS304 grade stainless steel and our CNC precision machined flanges are also constructed from billet 304 grade stainless steel.  All M135i & 335i models produced up to 07/13 require the 3.5″ version of this downpipe. M135 and 335i models produced after 07/13 require the 4″ model of this downpipe. All M235 and 435i models require the 4″ version of this downpipe. Please feel free to contact us with the last 7 of your VIN if you need help determining exactly which version of the downpipe your car requires.