is there a difference in size between the ITR axle back compared to a Si Axle back?

i want to keep a stock looking muffler and sound. i'll either get ES or ITR muffler

i'm getting a 2.5" b-pipe to match to the JDM ITR 4-1 header and 2.5" cat that on my car right now

 

I'm pretty sure the ITR piping is 2.25. What's the stock piping on your Si?

 

i dont know, probably 2"

it's a 2000 Si

 

R is a bit on the loud side for a stock muffler... its all relative though