welding question
 

iam making a test pipe for my 240. how thick does my pipe need to be, i have an apexi n1 catback already and i want to know how thick the piping should be for the test pipe, or does that not make a difference?? also, can i take the flanges from my cat and weld them onto this pipe that i bought?? also does the catalytic right now have an o2 sensor to it??? if so will i need to drill a hole onto the new pipe for it?

I don't know how thick your pipe has to be. I would think along the same width as your exhaust.

What are the test pipe and cat flange metals? What are the thickness? Depending on the metal you might have to change the type of welding you do. Heliarc is what is used for aluminum if I am correct. It is difficult to make the welds look good.

If you find that the welding is too much you can purchase a test pipe from PDM or Project Silvia.

I looked thru the FSM and the only mention of a O2 sensor is the one in the engine bay next to the master cylinder. So it looks like you will not be drilling a hole.