Flowmaster makes several series of muffler. The new 40 series is supposed to be a very nice sounding muffler. I haven't heard a set myself, but the guy at the shop that did my system said they had a nice Mustang rumble. The 50 series I'm told is LOUD!! So if you like your neighbors, you may not want them!
I went with the DynoMax Super Turbos. I have had them on 3 of my cars over the years, and I really love the sound....not to mention they flow like an SOB. :D (Again using the Mustang as the benchmark, that's about what I sound like at idle, with a very nice rumble as I accelerate.)
1993 Grand Marquis w/170,000+ miles and counting. Now it's time to make her FAST!!!
12" conical K&N filter, Custom side exit exhaust with X-pipe and Dynomax Super Turbo mufflers, replaced stock fan and clutch with PI electric fan and PSM fan controller, Aluminum PI driveshaft.
Body mods include a '95 Cobra rear spoiler, tinted windows, 17" Mustang Split 5-spoke rims w/ P255/50-17 BFG g-Froce TA radials, and a 14,000lb Auxillary Trans Cooler.
Interior: Custom A-pillar guage pod w/ Digital oil pressure and Trans. Temp. guages.