ran a new best of 14.5 97mph with a 330 60" and 2 10" sub . later i found out i had a burned out gasket on the b-pipe (thanks warspeed) and a exhaust leak where a clamp was used (thanks mieneke) would this cause a loss of performance? i had them weld the pipes together this time and install a new gasket ,i notice the hissing sound i thought was comming from the y-pipe is gone.

 

I had the same problem. I left the stock muffler on and got the WSP Y and B. The B pipe is a half an inch bigger and the connector thingy (cant think of the name right now) it slightly bent.

Mine started getting louder and I thought it was cool.
Then it started droning and I hated it. Then I heard air escape somewhere when i pressed the gas and my car was hella slow.

So I got it welded and Now im happy

 

I had a custom Y pipe built since I was tired of waiting for Cattman's a while back. Recently I took it to a shop and found out that I had 10 exhaust leaks coming from my y pipe. Dumb POS shop! Everytime I gassed it sounded like I had a wastegate, it mades this hissing sound. So a few days ago I bought a y pipe from cattman (they finally have it in stock, but those guys sent me the wrong gasket and stuff, man I wasted $15 on nothing). Now the hissing sound is gone, which is pretty cool. I noticed my car is a bit slower though, I don't know why. I'll have to keep driving it to see why that is. When you have an exhaust leak it's suppose to actually help for higher speeds, it just kills you low end. Hopefully that answers your questions.