Cliff, i run dynomax mufflers on mine, dont know about the db rating but they are a lot quieter than the flow masters i took off. The car picks up about 1.5-2 tenths with the headers open and 18" collectors.
Somebody on here posted a list of mufflers and their noise rating a while back.
Mick


69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200#
best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft
best 60ft 1.36