[84LX89GT]

With an offroad H-pipe and 2 1/2" tubing i had Flowtech Stinger Cat-back and i thought that they're actually TOO QUIET on my '84. Much quieter than flowmaster 3 chambers and i'd actually say probably quieter than most of the dynomax stuff i've heard. You can tell there's alot of baffling because the Stinger mufflers weigh A TON.
I'm putting them on my GT soon and with the offroad H pipe my exhaust will probably be quieter (i have fairly small holes in my left muffler but it's only slightly louder than stock). I don't have any Becibal readings or anything like that, but my personal experience is that the flowtech stuff is pretty darn quiet. The dynomax stuff is probably plenty quiet and probably lighter and better protected against rust, so i'd go with that. The dynomax super turbos really aren't loud at all.