abs....Your stock downpipe connects to your stock cat, then your cat back connects to it (which is just the rest of the exhaust piping from the cat plus the exhaust tip)...

When you get the new downpipe it will have a highflow cat built into the downpipe itself (so the stock cat goes in the bin!) and connect directly to the rest of the catback system(just connects to the mid-pipe), and it will be 3" all the way from the Turbo manifold...
Will definitely need a tune after that...
Cat back is just for sound, tbe for power and sound