What causes the differance? Where some have that low, strong sound, and then others make the car sound like it's about to fall apart?

Edit: Is there any way to know what it is? Like if I find one at the junktyard?

 

A lot of things make a difference.

My setup:

header>2.5" straight pipe>High flow cat>2.25" straight pipe>resonator>2.25" over axle bend>muffler

Without a resonator most cars sound less refined. The resonator helps remove raspiness, buzzing, and high pitched tones.

Muffler choice makes a difference too, but that's hard to know which one to pick unless you have heard the muffler you're considering. Search online for whatever brand you're looking at and see if you can find videos of cars with them installed. Another choice is to go to a shop that does performance exhaust systems and tell them what you want and they'll make suggestions that are much better than most other people you're going to talk to. You might be suprised, they may even be pretty inexpensive. Muffler included a custom catback exhaust should only cost you between $200-$350.

 

ive got 4-1 extractors stock engine pipe and cat
2 1/4 catback with big fcuk off sports muffler at the back
also got a hacked 2 inch catback to rear muffler system with a resonator in it

atm the 2 1/4 system sounds SH*T when its cold, it needs some temp through it then it sounds alright
when my tax comes i'll get a 2 1/4 inch extractors to highflow cat section made up and get the resonator put in the rear section