Has anyone taken out the B pipe on a 5th gen and replaced it with a custom mandrel bent pipe? I was thinking of doing this and was wondering if it will do anything sound and performance wise combined with my y-pipe.

 

Yup, ask y2kse about it. Last I remember, he was trying to sell his setup.

 

performance wise: unless you gut the cat or get a high flow cat it won't do much. Make sure that the place actually opens up the little "knots" in the piping sections. When you lift your car you will know what I mean.

Sound Wise: With stock muffler kinda quiet but you can hear it inside and out. With any kind of muffler. LOUD.

 

when modding the exhaust, work your way from the engine back... y-pipe, cat, b-pipe, muffler. Replacing the stock muffler will make things loud if you have modded your other exhaust components. I am going to mod everything, but leave the stock muffler on.....

 

That's how I have it too. I left the stock muffler on after installing the Y-pipe and removing the resonator..
IMO, it's just not worth the extra $$$ for a cat back system. Why? It was dynoed to have an extra 2-3hp WITH an open cat back! Besides, the stock muffler adds a stealhthier look and the y-pipe has a nice growl from about 2k rpm....sweet and low profile...cool..