SRT4 utilizes resonators and no mufflers to achieve its sound. Also, the exhaust is about a foot and half shorter since their engine is mounted intake side towards the front. I am going to try to make my own exhaust this summer and try to get as close to the SRT4 exhaust as possible and I will write a guide about it.
My plans so far are 3" downpipe, 3" flex, 3" cat, then split to 2 1.75" runners down both sides of the vehicle, and put a resonator or 2 on each side. Of course, this probably wont clear the ground, or have some other kind of problems, but its just in testing right now.