I am planning to get a jdm itr 4-2-1 header to mate up with 2.25" piping. I read that even though the outer collector size is 2.5", the actual inner size is just under 2.25", which is good because even stock 2.25" piping would have an inner diameter just under 2.25" right? But I still need to go with a 2.5" cat? Do I have to worry about tapering down after the cat?

 

just go to Kteller and get a custom cat that has a 2.5 flange for the header and a 2.25 flange for the exhaust piping

 

do alot of people have this setup? I'm just kind of confused about the inner diameters ... based on what I said above, wouldn't the collector be opening up to a larger cat and then exiting into a smaller exhaust pipe?

 

people with that setup run a 2.5" inlet cat with a 2.25" outlet typically. Just do what the other guy said and get one from Kteller and you'll be fine.

 

I guess I should be able to find a carsound cat pretty easily at an exhaust shop here in Toronto?