exhaust drone/harmonic resonance

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Jefflock,
Where about in KS. might you be? Want to try my VT's for a sample ride? I am close to KC, MO. They will fit right on an A-body with only a bit of pipe needed.
Tom
[email protected]
 

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My 67 GTS has always had drone even with the stock mufflers but it was a lot lower in level. Now as I went to performance type mufflers it got louder along with the rest of the exhaust. The last muffler was Accurate Exhuasts performance mufler for an A body. After the engine rebuild, mild, the drone is bad. Just tried a pair of straight thru Magnaflows and it's louder. It's currently unacceptable. I considered the Dynomax VT's but I was nerious about moving parts in a muffler and possible rattle. In another post I read Dynomax's reply to a guy asking about rattling of the VT's and they told him it wouldn't be a problem if you install a crossover pipe. Since I have stock exhuast manifolds, 2.25" front to back and no crossover pipe I didn't want to get expensive mufflers that would rattle.

My choices now seem to be a more restrictive muffler, lower exhaust level overall or installing resonator pipes on the system tuned to the frequency of the drone.
 
Interesting, I have absolutely no sound deadening in my car and I've got 2.5" inch pipes from manifolds to tail with supper 44's. Barely any drone at all from 1000 to 2000, little bit and it's quite as a mouse inside while on the highway, don't know why.
 
So here's what drone looks like on a frequency graph. The drone is the spike around 130hz. At times the two other spikes a little higher in frequency increase in level. This is with a 383, 2.25" pipes front to back, stock manafold and Magnaflows. Drone is from 2000 to 2300 rpm.
 

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7dswinger said:
Interesting, I have absolutely no sound deadening in my car and I've got 2.5" inch pipes from manifolds to tail with supper 44's. Barely any drone at all from 1000 to 2000, little bit and it's quite as a mouse inside while on the highway, don't know why.
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Apparantly there are a lot of factors that effect drone.
 
340 swing said:
Here is what I have. Stock exhaust manifolds (70 340) TTI down pipes, TTI X pipe, Had dynomax super turbos took them off and tried spintech sportman 3000. TTI over the axle tail pipes and TTI tips. The car sounds great from the outside. But inside it hurts your ears annoying resonating just want to jump out kind of noise. I talked to Ron at spintech and he suggested trying resonators in the tail pipe area. There doesn't seem to be enough room. Has anybody had any luck with this? I have way too much money invested in this to give up on it, any ideas would be appreciated.
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I feel you pain both in ears and pocket book.
 
Graph with dynomax turbo muffs. Drone level the same but other two peaks and rest of graph lower.
 

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This guy installed resonator tubes on his Shelby Mustang with electric cutouts on the resonator tubes. Interesting to hear with and without them. He says with them he can now listen to the stereo and talk in a normal tone in the car while curising.

[ame="http://www.youtube.com/watch?v=ijwxKDVnAec"]Cruise Loud or Quiet - Exhaust Cutouts Installed on Resonator Tubes - YouTube[/ame]
 
I have the Dynomax Turbos on now and they drone. They are also covered by the 90 if you don't like them Dynomax will buy them back and have UPS pick them up. So I'm taking them up on it and ordered the Dynomax VT's. We'll see it they work. The VT's have the same 90 buy back coverage.
 
pulse wave termination chambers prior to an H pipe prior to the mufflers on duals out to the bumper. Run large internal volume, large case turbo type or other absorbent mufflers.

Prevent sound pulse reflection up and down the pipe, balance - cancel sound pulses, dampen sound pulse and volume, try and maintain velocity and cfm.

Here is a thread full of practical application pulse cancellation and drone cancellation:

It requires some work. The modern factory exhaust systems have lots of acoustic and velocity tuning to make good horse power and still not annoy everyone.

http://speedtalk.com/forum/viewtopic.php?f=1&t=27535
 
Do the VT's have more throatiness to them ? I have the turbos and they are very mellow ..
 
65-440 said:
Do the VT's have more throatiness to them ? I have the turbos and they are very mellow ..
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At idle they remind me of a stock sounding 60's/70's muscle car. Still some drone but a lot lower in level and not ear rattling. More like stock drone,car had some drone with stock muffs. Drone is tolerable now. Once the valve is open it's a straight thru muff and it isn't as loud as the magnaflows. From my recordings the turbos sound a little deeper. Under normal driving conditions their not as loud as the turbos but they perk up when you do larger throttle openings.

For me too loud makes it hard to drive the car very long. No fun if you don't want to drive it.
 
buck351 said:
They get louder as you give it more throttle. At idle they remind me of a stock sounding 60's/70's muscle car. Still some drone but a lot lower in level and not ear rattling. Less than half the sound level of drone. More like stock drone,car had some drone with stock muffs. Once the valve is open it's a straight thru muff and it isn't as loud as the magnaflows. From my recordings the turbos sound a little deeper.

For me too loud makes it hard to drive the car very long. No fun if you don't want to drive it.
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I know everyone has theyre own opinion / tolerence on drone. i just drove 200 miles to a Mopar show and my exhaust to me was quiet. no unbearable drone. TTI headers and 2.5" H-pipe system w/ super turbos .... I think i want a louder muffler, either magnaflow or ..... gulp ... flowmaster 40 series
 
You need to run the pipes out the rear or at the very least, out hte sides. You have to get the sound out from under the car. Also, try adding a set of Dynomax bullets. I had a single 3" on my Bronco. After 2 hours, I was at the point of vomiting from the drone. It made my head hurt so bad, that I eneded up staying at a friends house just so I didnt have to drive. I added in a second bullet and the drone was about gone. Also, if you have an x-pipe, maybe swap it out with a 2 in 2 out style resonator. This is done on a lot of modified Tbirds that have the supercharged 6. Most prefer Borlas.
 
None2Slow said:
You need to run the pipes out the rear or at the very least, out hte sides. You have to get the sound out from under the car. Also, try adding a set of Dynomax bullets. I had a single 3" on my Bronco. After 2 hours, I was at the point of vomiting from the drone. It made my head hurt so bad, that I eneded up staying at a friends house just so I didnt have to drive. I added in a second bullet and the drone was about gone. Also, if you have an x-pipe, maybe swap it out with a 2 in 2 out style resonator. This is done on a lot of modified Tbirds that have the supercharged 6. Most prefer Borlas.
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Stock exhaust manifolds and 2.25" all the way to the bumper. Seems to be a number of variables that can effect drone based on the perticular car's setup. Basically you need to somehow stop the resonating of the drone frequency in the pipes. The level of mine has been reduced a lot with the Dynomax VT mufflers which I choose to try verses the resonator tubes which were more complicated but probably would have kill the drone all together.
 
Yes the resonating is tuned out with Helmholtz chambers on each pipe at a fractional order of the wavelength / frequency you want to eliminate.

The H pipe btw the exhaust tubes can serve as a dual hemholtz chamber and also connects each pipe together at the same time (I guess).
If you get lucky and arbitrarily or intentionally get the correct length H pipe between your exhaust tubes you help eliminate your resonation in two ways I figure.

This is pretty much the cat's meow, clean setup and bare bones simple too:

http://www.ls1gto.com/forums/showthread.php?p=8617677

Great links and info buck351! Thanks!
 
I was a muffler/ exhaust designer for GHL Motorsports for 6 years. Look them up. They're renowned for zero resonance high performance exhausts for Porshe and corvette. The key is to run packed mufflers with the right internal volume for the engine its being used on with bent perforated tubing all the way out the back of the car. The idea of making one universal muffler that works great on all applications is impossible. In my opinion, with a small block, using headers or manifolds and 2.5" tube with magnaflow style mufflers sound the best with little to no resonation. Although flowmasters sound awesome outside, we all know that they will make you want to poke your ear drums out while driving at a sustained speed.
 
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