I built a 3.5" true dual exhaust system for my G 8. Cat back. 4 x 3.5" tail pipes. It had no mufflers but got caught up with the PA inspection. The sound was awesome. The larger the pipe the larger the sound waves the deeper the tone. Small pipe small sound waves. You get that weed wacker sound like most of the imports. The gentler the bends also helps. I pie cut all my joints. I ended up taking the stock muffler cases and gutting them. I put new caps on the ends. I cut 2 x 3.5" holes in the ends. I then drilled 1" holes in the tail pipes sides. Slipped them over them and welded them up. Re installed the stock mounts to the pipes. Inspection problem fixed. I was surprised how much they toned the volume down. It fits in the stock location. No excess heat to the interior. They put good heat shields on the car. If you are able, building your own exhaust is very satisfying like nailing your own roof. Basic skills with an mig welder. A good grinder and plenty of discs and anyone can do it.