i have a ls or gsr tanabe racing medalion cat back(came from a wreck with swap pulled,so i dont know)..but it's on my gsr. i'm gonna get a jdm 4-1 header and a test pipe replacement for the cat.

is the exhaust a 2.25, or 2.5?? so will i need a pipe that reduces from a 2.5(header side), down to a 2.25(cat-back side)

thanks for any info

 

pretty sure the tanabe is 2.36