I have a 98 GT with series 40 flowmasters dumped.
This is a two part question.

I want to make it sound louder so I am thinking about adding an o/r x pipe. Which brand would be the best to use?
Also, by adding this, will my car still be able to pass the smog check test?

 

1. an o/r x is basically going to be the same 2.5" pipe no matter where you get it from unless you buy a stainless steel one.

2.I'm pretty sure you won't

 

If your worried about emissions then just get a catted x pipe. It will still be louder and pass emissions. Or you could get the o/r x pipe and then just swap it with stick mid pipe come inspection time.

 

or....if you wanted more of a loud/mean/muscle sound you should get a mac o/r h to go with those flow 40's!!

here is a sound clip of my flow 40's with o/r h pipe. its loud enough to set off car alarms.

http://www.youtube.com/watch?v=giAUwj5peDQ

 

VRS makes a great o/r x-pipe that is stainless for $245 shipped.
That's what I have in my room waiting to get installed

 

Yeah I would listen to what he's saying. Even tho I have flows with an x pipe I wouldn't recommend honestly unless you have headers. W/o headers it pops pretty bad. An h pipe matches the deep sound also the flows put out. That's y eventually I'm going to switch to a straight through muffler like slp's to match my x pipe and shorties. But thats just my opinion.

 

+1