They are different lengths. I do not care about that.

What is the final say on the diameter of the piping?

Are they both 2.25" or is the JDM 2.36"? I am pretty sure that the JDM is NOT 2.5".

Finally, would it be worthwhile to make the switch?

I have researched, and looked over almost 150 threads. I have googled. I still have no idea what the concensus is.

Discuss.

 

jdm itr is 2.25

 

I thought it was like this

the usdm itr catback is 2.25 OD
the jdm itr catback is 2.25 ID

the jdm itr header has a collector that is 2.5