I'm going to install a 2.5" "test pipe" i guess you would call it. Here's a link : CAT DELETE TURBO DOWNPIPE 1996-2005 AUDI A4 1.8T B5 B6 | eBay
Don't hate on the ebay pipe please, it't just a piece of metal and i'm not going to pay 400 buck for one. I haven't had a chance to really get under the car and look, but it seems like the stock exhaust is 2.25 inch, is this correct? So i'm planning on running the downpipe off the turbo, reducing down to 2.25" and putting a new race cat farther downstream, like under the passenger floorboard. Then extend to o2 sensor wire to reach after the cat. Then i'm going to replace the mufflers. I'm trying to make this as low cost as possible, and yes i will be welding it. See any problems with this setup? And btw i'm am nowhere near inexperienced so don't worry about that. Thanks in advance.

 

My indie shop is installing my Billy Boat downpipe kit as we speak. The downpipes are larger than the pipes to the exhaust and my exhaust system is still good (and I don't have the money to replace something that is good), so they are fabricating a reducer and will clamp it on. Or, they may weld it. I just asked them to do whatever will allow me to replace the exhaust in a year or two when it needs it, without screwing up the downpipe kit. So your solution for the pipes sounds good. I cannot speak to sensor placement. I am also replacing all the sensors as a precaution because my guy said they are good for about 100k and I have 197k on the car.

 

Thanks for the reply. Can you have your shop confirm the size of the stock pipe? It looks like 2.25" to me but im not 100% on that.

 

Bump.
Does anyone know the stock exhaust size?