[vin63]

Regarding your question about why an automaker uses a mandrel bender, it mainly has to do with mass production and volume over time (time = cost).

I run a 3-inch exhaust to the outside of the frame. The toughest part was the curved sections from the shorty header collector down under the rise of the front frame and then pointed back. A local muffler shop let me pick through his scrap of 3-inch tubing and bends. You can buy J and U bends (not too expensive). I pie cut the bends to make my curved sections from the collector. That muffler shop then swadged a few ends for me to slip fit a couple of sections.