Kool

I have a 86 951. And I have a couple questions about the exhaust system.

1. What is a good place to start with the exhaust system?
2. I am confused on the terminology. What is a Test Pipe? Where does it go? Does it replace the Cat?
3. Can you have an efficient exhaust system and still use the stock Cat?

and finally.

4. Where can I find a good exhaust at a good price.

Thanks in advance for the input.

Mark