Originally Posted by Sparky66
I agree with Chowbow about the flex joint. It's still early days to comment but long term use and reliability of any aftermarket DP's is very, very questionable. Only one aftermarket DP manufacturer, called Supersprint Exhausts, have provided a flex joint at this stage.
Since DP's carry the hottest exhaust stream in all the system, it's natural that there will be a lot of metal expansion and contraction going on in there! Welded joints to flanges and pipe joints will need to stand up to long term heat induced movement in this part of the exhaust system.
Having flex joints in each DP is a no brainer and could help alleviate any undue metal stress inflicted cracks or weld failures to the downpipes.
If you think downpipes don't move at all, you are fooling yourself. BMW's engineers knew better and thats why factory DP's have flex joints.
Something to think about.
Some of the flex can be absorbed by the exhaust hangers, but I think the flex joints will help with tolerance issues too. Heat expansion, a slightly misaligned welding joint (and there are tons of many DPs) can easily be taken care of with a flex joint somewhere in the system. DPs definitely move around... Pop your hood and rev the motor and you'll see the whole thing flexing around on the motor mounts.