Exhaust Manifolds with Dynomax Mufflers?

charger70 said
I have a 71 Duster 360 auto w/ 3.23 rear and a 340 grind cam. It has 340 HP manifolds, Dynomax turbo style, TTI 2 1/2in full exhaust w/ H pipe. It was a lot louder than I expected. Especially about 50-60mph. Not as bad at freeway speeds above 65. It was annoying trying to have a conversation. It was bothersome enough that I put a set of larger Flowmasters for a SUV trying to quiet it down.(160$) It didnt help. I am still looking for a quieter set but havent found any I like yet.
Click to expand...

Do you run a vacuum advance distributor? I have the identical exhaust set up as you had, stock 340 cam in a 340, but 3:91 gears. At certain cruise speeds (around 35-40) I had a very loud drone in the passenger's compartment. Loud enough my wife was complaining. I adjusted the vacuum advance to only allow 10 degrees at the highest vacuum signal and the drone is all but gone. If you do have a vacuum dist. disconnect the vacuum and drive it around and see what happens.