Yup. Weight gains with duals. If you are going for looks though, sexiest mustangs ever have the dual chrome slant cut SS tips... Mmmm... dont do true duals off the header/manifold. Y-pipe it near the back. Less weight that way.
Honestly, nothing except; more weight a headache and some permanent hearing loss. If you had a full blown race motor, this might be of value to you, but not in this case. For the sake of argument, let’s say that you did see a big increase in gas flow from this (you won’t), now you would need to change fuel trims in order to compensate for the lower back pressure in order to realize a power increase. If you are going to spend some money on mods, make the money count and install a header with some 2.5” piping and a regular muffler. Yes, I know that’s what everyone else is doing and that’s because it really works!
well i went out to look at different mufflers and ended up getting a super 44 magnaflow muffler. i went out to a nearby muffler shop and got it installed to 50 bucks and let me tell ya ,,, i love the sound. its just perfect. not too (in your face) it has a very deep tone to it.
on my '91 i used a walker sound fx 5.0 muffler and 5.0 LX tailpipe with a ranger header and hi flow cat. At idle it sounds like a V8, and at speed it sounds loud enough to notice with a decent tone for a 4 banger.
No retarded tractor or weed wacker Honda sound here...