This is the situation. I have a T1R exhaust only the axle back section and it doesn't look like I will be getting the b pipe and test pipe any time soon since they are on back order from AJ-Racing. Do you think there will be any power gain using the stock ITR B Pipe? The rest of the exhaust doesn't come until May.

 

If it fits on the stock b-pipe then install it.

You won't really gain any power but the noise will be there.