# Drone & moving mufflers



## CTCarGuy (Nov 17, 2009)

I've been dealing with drone at 1800 to 2200 rpm in my stock 400 71 GTO hardtop. I've got a heavy duty 200R4 with lock up converter. 
1. First I put Pypes street mufflers on with an H pipe. No good.
2. Changed to an X pipe. Still no good. 
3. Put resonators on the rear tip - some help but not much.
4. Changed to Turbo mufflers - Very quite but still droned.
5. Install sound insulation throughout interior - some help.
6. Tried resonators before Pypes mufflers. No good
7. Put 12" resonators at the rear. No help.
8. Installed Dynomax VT (muffler with valve) Finally no more drone but TOO quiet.

My next experiment this week is:
1. Take out the X pipe and keep each branch separate.
2. Reinstall the Pypes mufflers (they sounded the best) but move them forward about 6-12". I may try moving them not in line with each other. 

I'm not concerned over any power loss by taking the X pipe out. I want a fairly quite cruise, nice sound at idle, no drone and a real "bark" when I get on it. Has anyone tried moving the mufflers forward??

Opinions? Suggestions?:seeya:

CT Car Guy


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## Pontiacpurebrred (Jun 22, 2011)

Well since you asked. Here is my opinion. And that's all this is ... opinion. 

Personally I think the stock exhaust sounds the best and never drones. changing the placement of the mufflers will probably not make a sizable change in the sound it makes. 

What size are your exhaust pipes? 

I have heard (and I am no expert) that larger diameter than needed pipes will cause a droning sound. I assume removing the back pressure is what causes it. So that may be your issue since it sounds like you have tried everything else. 

What size pipes are you running?


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## geeteeohguy (Feb 2, 2008)

X2. Anything more than 2 1/2" diameter pipes on the street is overkill and doesn't help performance. Not a fan of obnoxious mufflers, personally. I have Walker turbo's on the '65 with a 2 1/2" system with Hedmann headers, no drone, and the '67 is bone stock with Midas mufflers....dead quiet.


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## Instg8ter (Sep 28, 2010)

yep the back pressure is where we get our GRRRRRRRRRRRRRRRRRRR, i like a nice idle, low mellow rumble, nice motor hum when cruising and a deep growl when i dump the secondaries, running 2.5" Summit pipes out of Hedman 3 pipe headers on a 462 true dual all the way back with magnaflow mufflers and it fits the bill. I don't want them to hear me coming, only going. Hate "hearing" over piped 302 mustangs from a half mile away. As i was coming home late tonight a local cruise in was getting out and a red 65' stang came running up hard behind me in my truck....i would have killed to have been in the Tempest with the new stroker and dual quads under the hood, know he woulda had a big weight advantage but i would have loved to see him try and pass the 326 badged family car....


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## BearGFR (Aug 25, 2008)

Instg8ter said:


> ... he woulda had a big weight advantage but i would have loved to see him try and pass the 326 badged family car....


Just be sure you keep it well and thoroughly waxed so that it's easier to keep clean... beacuse I know you woulda sucked the paint clean off that Mustang when you left on him. 


On the drone question, I'm running 2 1/2" pipes all the way from the headers to the rear bumper, X-pipe, and Pypes "Race Pro" mufflers on the Beast. No drone, and reasonably quiet --- unitl I hit the loud pedal.

And on the size question, yes Virginia it is possible to have tubes that are too big. Not only will they drone, but they'll kill flow velocity and with it - some low end torque.

Bear


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## CTCarGuy (Nov 17, 2009)

Thanks for the input. The car has stock exhaust manifolds into 2.5" pipes. Even with the "stock" pipes and Midas Eagle muffler, it droned like crazy. I've heard the 71 body has a resonance and that Pontiac put resonators on the GTO's, which everyone took off of course.

One other thing I tried - It was suggested to only use the stock hanger behind the muffler. A pain to put in but no help. 

I will continue experimenting. I set up the exhaust system with stainless steel band clamps so I can easily disassemble it at any time. Once I find the solution, I will weld it up.:lol:


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## allpawl66 (May 9, 2008)

Install Flowmaster Delta-Flow mufflers , no drone ever , all noise out the tailpipes , no interior resonance , have them on a 68 bird , 400 w/headers .


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## BearGFR (Aug 25, 2008)

CTCarGuy said:


> Thanks for the input. The car has stock exhaust manifolds into 2.5" pipes. Even with the "stock" pipes and Midas Eagle muffler, it droned like crazy. I've heard the 71 body has a resonance and that Pontiac put resonators on the GTO's, which everyone took off of course.
> 
> One other thing I tried - It was suggested to only use the stock hanger behind the muffler. A pain to put in but no help.
> 
> I will continue experimenting. I set up the exhaust system with stainless steel band clamps so I can easily disassemble it at any time. Once I find the solution, I will weld it up.:lol:




Nice car!!!!!:cheers

Good luck with getting it how you want it.

Bear


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## CTCarGuy (Nov 17, 2009)

*Experiment #1*

I took off the X pipe and replaced it with straight pipes like the car was set up with as new. I installed the Pypes Street mufflers and off I went on a hour plus driver on the highway and back roads. First I noticed there was no drone at all! The car sounds great (barks!) when I get into it and mellow at idle. The sound is not bad on the highway at 70 or so with the windows open but anything more than an hour or so of constant speed might start to get to me. The car never sounded so good!

Experiment #2 - Next I'm going to replace the Pypes with the Dynomax VT mufflers and see what it sounds like. I think I'm on the right track.


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