# Boom ******



## CTCarGuy (Nov 17, 2009)

My 71 GTO is driving me nuts with the resonance between 1600 and 2100 RPM, just the range I use most often. On the Hot Rod Power Tour, it was so loud my co-driver could not hear me. This is on a stock 400.

The exhaust is new using 2.5" pipes from a stock manifold into an X pipe (tried an H, it was worse) feeding Pypes Street Pro mufflers. All of the joints are welded. I added a pair of resonator exhaust tips and they help a little but reduce the exhaust sound throughout the entire range.

I know that GM did not use a donut between the manifold and front pipe. Could this be part of the problem? I thought about somehow isolating the hangers on rubber where the bolts connect to the body. Would adding sound deadening to the interior help. 

The cars sounds great at idle and slow cruise and also sounds great when I'm on it. It's the in between thats a a pain. Ideas??


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## 05GTO (Oct 6, 2004)

What kind of hangers are you using?


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## 66tempestGT (Nov 28, 2009)

im sure sound deadening would help. lots of people use spray on bedliner material. pull the seats and the carpet and blast it.


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## geeteeohguy (Feb 2, 2008)

The problem is probably your mufflers, IMO. With low restriction higher flow mufflers, this is common. Sometimes the resonance happens out of the "sweet spot" and you get lucky, but a lot of times it is right where yours is....at cruise. You must have pretty tall gears to be running where you're at. Solution: change the mufflers for quieter units, or change cruising RPM. Your problem will not occur with a stock exhaust system. (but how much fun is that??)


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## aggie88 (Aug 13, 2005)

I am actually considering the Pypes mufflers and 2.5 inch header back exhaust too. 

I don't believe hangers will help reduce resonance. It is the mufflers. Muffler resonance is a big deal on corvetteforum. I have had three Corvettes and any aftermarket muffler will create resonance. In fact the mufflers I am using now on my 05 Corvette are the factory Z06 vacuum actuated bi-modal mufflers. When in the open position, it rattles your eardrums when the engine is under load at certain rpms. But when I close the baffles, voila, the resonance disappears. But as the other poster said, "what fun is that?"

You may want to investigate Corsa mufflers. They build mufflers for Corvettes that are louder than stock but produce no resonance. However, they achieve that at the expense of pitch or tone. Many describe the Corsa muffler as more of a European exhaust note, not a muscle car V-8 rumble.


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## ALKYGTO (Mar 29, 2010)

I run the Hooker Aeroflow mufflers, the full bodied ones, not the race mufflers and I really like them. No resonance at any speed and I'm running 3 1/2" pipe and channeling the exhaust of an 800+ hp engine through them. Not to mention they are priced right.


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## Rukee (Feb 8, 2007)

I'm running the dynomax muffs from NAPA, granted they could be a tad louder, but no resonance at all at any speed. Nice and quiet in the car.


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## GTO JUDGE (May 14, 2005)

Sounds like a similar set up I have...

I have X pipes 3" Pypes Street Pro system with mufflers. 3" to reducers at the tips. Car sounds great but a loud droan at about 35mph at times its annoying and the music has to be turned up and normal range talking is hampered. Can't tell you how many people have complimented the sound and people actually stopping me in traffic asking what I have on it. I do not though, have the issue you describe, the hangers appear to be "normal" and all is welded together.


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## geeteeohguy (Feb 2, 2008)

I've run the Walker Turbo mufflers on my '65 for the past 20 years. I have Hedmann Headers on the car, and 2 1/2 inch pipe all the way back. No resonance at all, but my normal rpm range is 2400-3500 rpm with the gears and std trans that I'm running. I think that the more an engine is lugged in the lower rpm ranges, the greater the chance for the bass drum effect.


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## CTCarGuy (Nov 17, 2009)

Thanks All:
I took the car on a 80 mile trip using back roads and the drone is miserble. I had Raven mufflers and it was the same problem. I've tried several mufflers and the problem persists. I don't want to change the mufflers if possible. My research is that at a certain frequency, the exhaust resonance matches and the droning occurs. The answer given is to make the length of the pipes uneven. I tried that by adding a resonator tip to only one side. Better but still there.

I was holding a partially full cup of Duncan Donuts coffee and I could actually feel it vibrating! I can also feel it in the floor through the carpet padding and the carpet. There has to be a way of canceling the frequency. I wish I had a frequency meter. 

The quest for the solution goes on.


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## GTO JUDGE (May 14, 2005)

The popular mufflers of the 70's were glass packs, hush thrushes, and cherry bombs, may sound old school but have you considered them now? I would think someone would have something like them? Some I know love Flowmasters on the old ones.


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## Too Many Projects (Nov 15, 2008)

geeteeohguy said:


> I've run the Walker Turbo mufflers on my '65 for the past 20 years. I have Hedmann Headers on the car, and 2 1/2 inch pipe all the way back. No resonance at all, but my normal rpm range is 2400-3500 rpm with the gears and std trans that I'm running. I think that the more an engine is lugged in the lower rpm ranges, the greater the chance for the bass drum effect.


Right on, MAN, I had a pair of Walker Red Line Z's on a 70 Monte Carlo and they were KILLER !!! Loved them. Wish I could still get em...

I also had a Flowmaster system on my previous pickup and HATED the drone. I'll never get another Flowmaster again.

Read the reviews on the Pypes mufflers and this is a common problem with the Street Pros. They are tuned to sound aggressive and that's what happens. That's why I got the Race Pros. They are straight thru and actually quiter under cruise and idle conditions and I have very little resonance under certain part throttle conditions only. And NEVER weld the system solid until you are certain you like wht you have...


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## geeteeohguy (Feb 2, 2008)

I agree, TMP. 100%!!! I HATE Flowmasters! I hate big wheels even more!!! I guess it's because I'm from Oakland, CA, and that ghetto stuff got old after several decades. I love the old school turbo muffler sound....you can really hear the cam, but no drumming. Not really loud, but just the right raspiness. The only way for our friend to get rid of the drone without changing the mufflers would be to change the RPM the drone and drumming is happening at. It sounds like he's got an auto and a tall gear like a 2.56 or 2.73....he's running around at less than 2000 rpms. A change to a 3.23 or 3.36 would take care of THAT in a heartbeat!!!


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## Eric Animal (Oct 28, 2007)

Cherry Bombs, disturbing the peace since 196?.........arty:


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## GTO JUDGE (May 14, 2005)

Eric Animal said:


> Cherry Bombs, disturbing the peace since 196?.........arty:


and in 1975


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## jetstang (Nov 5, 2008)

1968..
I have Edelbrock RPM's on my 70 and they are loud, but don't drone. I had a 77 Trans Am that droned all the time. My uncle said on his mufferless truck that it was bad and he cut the pipes to different lenghths. Try turnouts so the sounds don't reverb off each other. Your pipes do run to your bumper?


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## CTCarGuy (Nov 17, 2009)

Update:
I installed all of the proper hangers. no help. Next I put on a set of Dynomax Super Turbos. Car was quiet (actually too quiet) at idle but the buzz at 1600-2100 still there. Test #3 was to put on a pair of 12" Cherry Bombs at the rear. No help. I took off the Dynomax and put the Pypes Street Pros back on with the glass packs in front of the muffler. Sounds good at idle and the buzz is between 1800 and 2100. FYI - I put in double sound proofing throughout the interior and trunk. Gears are stock 3.55. I'm going to return the Dynomax. They suggested the VT but I have reservations about the valve. Maybe what I hear is more of a European exhaust only when under load. Dynomax said taking the X pipe off would not help. Next experiment is to wrap the header pipe before the X to see it makes a difference. I have less than 2 weeks to resolve this before we go on a 5 hour trip to Vermont. If I ever want my wife to go with me agin in this cr, I need to quiet it down, even if its temporary. Suggestions?


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## ppurfield001 (Jan 21, 2008)

CTCarGuy said:


> Update:
> I installed all of the proper hangers. no help. Next I put on a set of Dynomax Super Turbos. Car was quiet (actually too quiet) at idle but the buzz at 1600-2100 still there. Test #3 was to put on a pair of 12" Cherry Bombs at the rear. No help. I took off the Dynomax and put the Pypes Street Pros back on with the glass packs in front of the muffler. Sounds good at idle and the buzz is between 1800 and 2100. FYI - I put in double sound proofing throughout the interior and trunk. Gears are stock 3.55. I'm going to return the Dynomax. They suggested the VT but I have reservations about the valve. Maybe what I hear is more of a European exhaust only when under load. Dynomax said taking the X pipe off would not help. Next experiment is to wrap the header pipe before the X to see it makes a difference. I have less than 2 weeks to resolve this before we go on a 5 hour trip to Vermont. If I ever want my wife to go with me agin in this cr, I need to quiet it down, even if its temporary. Suggestions?



I had a little drone with the "quiet" Magnaflows with a 3.55 rear. Installed a Keistler five-speed manual transmission, which keeps the car at about 1,900 RPMs at 60+. No more droning. Good luck.


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