Ok i've heard that the JDM & USDM ITR exhaust piping are the same diameter. the only difference is the length of the cat? Then how come the JDM 4-1 doesn't fit USDM ITR without modification? Can anyone explain?

 

JDM header has a larger collector, therefore requires larger cat. Past that, you're on your own. I have no idea what the JDM cat outlet size is, nor the JDM b-pipe...

 

I'm guessing the JDM inlet is 2.5 but outlet is 2.25 the rest.

 

JDM b-pipe is longer, JDM cat is shorter, JDM header is same length as U.S. header

JDM header has a 2.5" opening to mate to the JDM cat
US header has a 2.25" opening to mate to the U.S. R/LS cat

 

i believe.. from what i have heard, both inlet flanges on the b-pipe are 1-3/4".

 

JDM header much farther under the car than USDM header. Cat is shorter on JDM but I cannot guess what B-pipe is but with a longer header and a shorter cat I would think the JDM b-pipe would be shorter or equal to USDM.

 

JDM B-Pipe length == USDM 94-99 GS-R B-Pipe length.

 

NO.

 

Right on the money
Just so everyone understands, were just talking length. Pipe size and design do differ from a GSR's

The JDM Header is about .75" longer than the USDM header

The JDM Cat is about 12" long

JDM ITR B Pipes (Just like USDM GSR B Pipes) are about 5" longer than a USDM ITR B pipe

Did I miss anything

 

Isnt GSR B pipe crush bent, and R mandrel?

 

Seems the people that sell the parts and make the cats to make the parts work on USDM cars disagree. Any reason you in particular you have this differing opinion than everyone else?

 

Chris: Yes, which is why Mike said they differ in design

Trey: They are different lengths, like mike said the JDM is slightly longer, but like Dan's test pips, you CAN make it fit even if it's too long (ok, please don't take that out of context )

 

SMSP said USDM header is 2" OD.
The Euro header at least has a 2" flange. The JDM header is longer than the Euro header.