rsr catback...3" high flow cat?

[theycallmebruce]

i have an RSR catback. i read somewhere on this board that the piping diameter is close to 2.75"

question: from the turbo back, the exhaust piping should step larger and not smaller from what i gather. i was speaking with a guy who's worked on DSMs for many years and he said that the cat is gonna be a restriction anyway so if i go 2.5" to the flex, then 3" to the 3" cat, it should be ok. the smaller catback piping won't cause any more restriction or turbulence because it will hit the cat before it anyway, which is a larger restriction.

if i get a race pipe to swap in, then it will become an issue?

 

[DSMeclipse4G63]

ok I am guessing that you wanna know if you get 2.5 into 3in downpipe and cat that having a smaller cat back will matter...if so yes it will. anytime you go from big to small you will loss some flow, even if its after a cat. Modern day cats dont really restrict as much as people say they do and a high flow will most definatley flow more. I am by no means saying a rcae pipe isnt better flowing then a cat. just go from one size to bigger or all the same size.
Andrew