Exhaust noise

[Blair Harris]

Hi i have a 1967 Dart GT 383 with manifolds 2 1/2 dual exhaust front to rear flowmaster mufflers. At about 1600 rpm i start to get a high pitch sound and it increases to about 2400 rpm. To a point you cant hear the radio it drop of almost completely at 2500rpm. I have done some research and a lot of the suggestions are to install a cross flow pipe.
Anyone else had this problem and tried this as a solution?

 

[Abodybomber]

Flow masters "resonance" happens between 1500-3000 rpm. The old "2 chambers" are the worst. My big block El Camino,drove me nuts. I would look at a crossover,and some Ultra Flo's,or Super Turbo's.(both by Walker exhaust). Tried the crossover with the Flowmasters.It raised the resonant point ,higher in rpm. That's all.

 

[pntastar69]

Get rid of the flowmasters and you'll get rid of the drone.

 

[roccodart440]

I'm in the rpocess of ridding my car of the slowmasters as well. Too loud inside. One other thing to consider is in through the muffler drags going to a stright though design picks up almost a 1/4 second. The performacne just isn't there.

 

[Blair Harris]

Hi thanks for the advice,i did put the cross over pipe on and it slightly reduced the noise still a huge problem. So i will be taking your suggestions and looking into the Walkers seems like the quickest fix.

 

[buck351]

If its a spike in a give frequency at a given rpm, drone in my experience, it can be eliminate by using a branch resonator on both tail pipes. They are not in the exhaust gas flow but branched off the tail pipes. You can put an app on your smart phone that will show you a db verses frequency graph and you can see the spike appear. Once you know the frequency you can calculate the dimensions for the resonator.

Yesterday I put them on my 67 GTS. No drone. Check out the thread about suggestions for mufflers without drone. I tried a few including the Dynomax VT that is suppose to stop drone. The VTs reduced it 12-14db in my case but didn't eliminate it.. The branch resonates wiped it out.

 

[Blair Harris]

Hi thanks for your reply, do you have a manufacturer name and a part # for the branch resonators. Also what is the smart phone app called ?
Thanks Blair

 

[buck351]

You have to make the branch resonator installing it yourself of you could have a muffler shop make and install it. You have to first know the frequendy of the drone. You can calculated it but I just measured it with an app for my Andriod phone called FrequenSee - Spectrum Analyzer. Then instead of using an equations to calculate the size of length of the pipe I used this site http://www.diracdelta.co.uk/science/source/q/u/quarter wave tube/source.html . You have to have a flat cap/end on the end of the resonator. It won't work if you crimp it down and weld it. A muffler shop tried that for a guy and it didnt' work.

Look at this post, http://www.forabodiesonly.com/mopar/showpost.php?p=1970058090&postcount=68 , to see where I put my resonators on my 67 GTS. If you look at the rest of the thread you can see my plots showing the drone frequency.