If it has manifolds, they are 2".
If you have headers, Chryco is right, 2 1/4"
The best way to get a good sound, is run smaller pipe, to the muffler, and bigger pipe out the other end.
(ex, 2" to X pipe, 2" X pipe, to 2 1/2" mufflers, 2 1/2" out of mufflers)
X pipes sound neat. Seems no one here even knows what a X pipe is, and everyone comments on how my trucks sound.
Walker turbo's sound nice, and are cheap. I have some on my 95 ram, nice muffler for the price.
Magnaflow's are my new favorite, I really like the sound, like a mellow glasspack, but they dont blow out.
Flowmasters sound funny to me. (and, despite the name, really don't flow)
Areochambers are my tried and true performance muffler, sound great, and better with some header!
Glasspacks are good performing mufflers, no doubt about it, but the noise they make after they have some miles, is awfull. Kinda like that laboring old Dodge power winnabago you hear, with the JC whitney one size fits all glasspack dual exhaust sound.
Horrible. Just horrible.