Does anyone know the diameter a test pipe needed to replace the 2nd cat in a R56S? Is it a standard 2" inside diameter?

 

I had them do a 3" on my r56, but I only took out 2nd cat and resenator I still have the muffler but it sounds great.
Ben

 

stock pipe is 55mm

 

Sorry to be a noob, but what's the advantage in removing a cat? Extra power or just noise?

 

I went ahead and replaced the cat with straight pipe. According to the welder the inlet was 2 1/4" and the outlet was 2 1/2" (or maybe the other way around). I haven't noticed any power gains. Since it's not monitored it can be removed w/o any lights going off for extra noise. In my case I removed it because the Manic tune in my Mini has the flame option and both cats have to be removed.