Some exahaust questions, could someone give me the run down? Options

[tonytutino]

Ok so here's the plan: i would like to get rid of my stock exhaust piping, get a new muffler ( i got some nasty 3A racing one right now), and get a high-flow cat.

1) i want 2.25 piping so should i buy the 2.25 high flow cat? it may seem obvious but i really don't know.
2) we don't have emission laws here, should i get a test pipe instead? (whats the difference)
3) does the inlet of the new muffler need to be 2.25? alot of the ones i'm looking at are 2.5 and i didn't know if they welded some kind of adapter or something on there.

i guess thats it, i'm a newb when it comes to exhaust...

thanks in advance!

[Hanyo]

The cat helps make your exhaust note quieter. I highly recomend you keep a cat on your car unless you have some serious mods to support a test pipe. The world is polluted enough as it is.... If you get a high performance cat, makes sure its the same diameter as your piping, or you might as well stick with your original one. There are isn't much of a performance increase switching to an aftermarket unit.

I recomend you try your best to keep your exhaust diameters as close to the same size as possible. The weakest link in an exhaust is the smallest diameter. So if your getting a 2.25 cat, there is absolutely no reason to use 2.5" piping (unless your getting crushbent).

If you have a 2.25" inlet on the muffler and a 4" exhaust outlet, it will actually project the sound louder. Kinda like the flared opening of a trumpet.