Originally Posted by swamp2
I would bet the tubing is hydroformed, this process uses very high fluid pressure along with a "mold" for the outside shape desired. The tubing is very purposefully shaped into a non round cross section in certain sections. My guess (without looking under my car recently) is that it is for clearance - either to other parts of the chassis or to the ground.
On another note we debated the need for exhaust shields quite a bit on this thread. My conclusion was just what IND is saying above. A user installed heat shield sounds like a darn good way to play it plenty safe with any aftermarket exhaust system. Link to that thread here
Yes, the M3's OE exhaust system is manufactured by Arvin Meritor using an internal high-pressure hydroforming molding
process.This technology allows them to manipulate the size and shape of the exhaust tubing to fit tight areas, that would normally cause clearance problems.
Without the use of this technology, it would lead to unwanted NHV in the interior cabin.
Arvin Meritor has been the primary OE exhaust supplier for BMW for several years. They were the first exhaust company to make a tubular exhaust manifold using this new hydroforming exhaust molding technology in the early 1990's.
They have a factory located in Spartanburg, South Carolina near the BMW plant.