Ive been thinking about buying a jdm header, and a carsound cat; but Ive been wondering what kind of cat does the jdm type r have, and also does the jdm stock catback have a larger diameter? Which also brings up the question how/why can I get good hp from the jdm setup, if the jdm itr is only rated at 2 horsepower above my usdm spec?

 

A highflow cat for GSR will make the JDM exhaust bolt on for the ITR.

 

I think it's not rated much higher in power with the better 4-1 2.5" header because the JDM R still uses a 2.25" exhaust with a 1.75"-2.0" bottleneck at the b-pipe flange.