Stock downpipe is from turbo to cat. But you can get unrestricted ones that are a little larger in diameter
ok, so my TDI has a tubo back exhaust as stock
a CAT back system leaves the turbo downpipe and CAT but replaces the center pipe and backbox
a turbo back system just replaces all the existing exhaust components with larger bore ones and has an option of removing the CAT
a straight through system removes CAT, center muffler (if there is one) and rear muffler and replaces it with one big pipe from turbo all the way down
and finally, a resonated system has baffles in and a non resonated system does not.
is that correct?