Suggestions for muscle car sound muffler without drone

Mopar Exhaust Systems

  1. perko

    perko Well-Known Member

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    Hi everyone, I know this is an old thread, but it seems to be the most comprehensive when it comes to constructing these resonators. The previous write ups are great, especially the part where the computer does the math for me. I'd really like to nail down a good method for fabricating these things and still have them look good. That being said, I have a few questions if anyone has any input.
    • Does anyone have any more photos of the install locations, or suggestions on where to rout the resonator chamber after living with their setup for a bit?
    • The chambers must be mounted after the muffler correct?
    • I have read that they need to be mandril bent or the sound wave won't make the turn. Has that been everyone's experience? It looks like buck351's resonator is not mandril bent.
    • Also, much of what I've read says that the bend should not be over 30 degrees and are ideally perpendicular to the flow of the main pipe, however the ones posted here appear to have 90 degree turns off the main pipe. Maybe this is only if the pipe is making a continuous bend?

    I have a 67 318 with 920 heads in my 73 duster with 1.25 pipes and dynomax super turbos and an H-pipe cross over, but I've got an obnoxious low rpm drone.
    Thanks for the input.
     
  2. perko

    perko Well-Known Member

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  3. buck351

    buck351 Well-Known Member

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    20130712_212133.jpg 20130712_212139.jpg I got the 90's and the straight pipes from Jegs or Sumitt to make mine. The 90's were a smooth bend that's one of the reasons I bought prefabed ones. I also used a slip fit on the pipe where it connects to the 90 so there could be some length adjustment/tuning possible. 2" tail pipes with 1.5" resonator. Maximum effect would be a resonator the same diameter as the main pipe but the DB calculation on the resonator looked like it would be enough with the 1.5" pipe and the smaller pipe would be easier to fit in places. The clamped fittings don't look as nice as welded connections but I figured it would be easier to remove the tail pipe if the resonator could be removed.

    I would think your Duster would have a similar void where I put mine.
     
    Last edited: Jun 8, 2016
  4. perko

    perko Well-Known Member

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    just top be sure, you installed a resonator on each side correct?
     
  5. perko

    perko Well-Known Member

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    Here's a good video on it. I think that he incorrectly refers to it as a Helmhotz resonator, which from my research appears to be more of a spherical void resonator that works on a similar concept. I think the technical term is 1/4 wave resonator.



     
  6. buck351

    buck351 Well-Known Member

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    Yes. There was a part of high school physics called wave physics where you studied waves and there interactions and you probably thought when would I every use this information. Here ya go this is it. :)
     
  7. buck351

    buck351 Well-Known Member

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    I watched the video link you posted. He was talking about trying different resonators to see if it eliminated the drone. Trial and error is a lot of work when you can just measure the frequency at the rpm it occurs, calculate the size of the resonator, install it and your done.
     
  8. perko

    perko Well-Known Member

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    Yeah, constructive and deconstruction wave interference. I just put the video up incase someone wants more information. I plan on just fabricating some myself. Any advice on the adjustable portion? I was thinking of just flaring one of the pipes so that it can slide an in

    Its funny, the NoDrone guy from the youtube video suggests putting the resonators as far forward as possible, but another company that I contacted for advice (Solo Performance Exhaust) recommends putting them as far back as possible. After looking over their sites, Solo appears to make a superior product so I think i'll go with their advice. Here is a link to some of their systems. Their systems look really clean, especially the resonators. They'll sell them to you for only $195 a piece. what a bargain!

    http://solo-performance.com/images/performance-kits/3511/6full.jpg
    http://solo-performance.com/images/performance-kits/3511/3full.jpg
     
  9. buck351

    buck351 Well-Known Member

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    The 90 I used had a flare you can see in the photo and it was long enough to allow some adjustment. You could also make a cap for the end the you clamp on to get some length adjustment. If you did both you would have inches of length adjustment to the length if you had to tune it. I don't think you'll need to tune it if you measure the actual frequency of the drone and make it for that frequency. If the drone is really bad use the same size pipe for the resonator as the main pipe. I got away with a smaller diameter pipe but I also had mufflers that reduced the drone by 12db. Dynomax VT mufflers are advertised to get rid of drone but they just reduce mine by the 12db.
     
  10. perko

    perko Well-Known Member

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    I'm trying to get rid of drone at about 107 Hz. After doing the calculations its just over 31 inches, which might just barely fit in the back after the mufflers, however it would fit much better along the straight pipes after the downtubes. Do you think that my calculations will be off since the resonators will be placed before the mufflers? It seems like they would change the pitch of the drone that I am trying to eliminate.
     
  11. buck351

    buck351 Well-Known Member

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    From what I've read people have installed them in front of the muffers with success. I would think as long as you ars elinminating the offending frequency it should be fine. Don't forget it's the entire length including the radius of the bend in your 31".
     
  12. Robj

    Robj FABO Gold Member FABO Gold Member

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    I just saw your reply. After first reading about this, I searched all over the net to see what people were doing. There's photos on truck sites, Mustang sites, Chevy sites- all over. Many people are doing 90 degree bends. Perhaps less than 30 is optimal but the 90's work very well. It's been two years for my daily driver Dart and I couldn't be more happy. I bought my pipes I used from Summit racing. It was actually cheaper than having the muffler shop in town make me pipes. I checked. I was ordering other stuff for my car so I had free shipping.
     
  13. dartnabout

    dartnabout FABO Gold Member FABO Gold Member

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    Looking forward to hearing them.
     
  14. buck351

    buck351 Well-Known Member

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    I see the website to calculate tube length and show you all the harmonics is not valid anymore. So here's the equation
    Frequency (f) = Velocity of Sound (V) / WaveLength (Lw). Assume a working resonator temp of 50 degrees C (122 F): V is 1187 Ft/sec. So knowing the frequency and velocity of sound you can calculate wavelength. Wavelength divided by 4 will give the quarter wavelength for your pipe length.
     
  15. BigBlockMopar28

    BigBlockMopar28 Well-Known Member

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    We have the big Thrush glass packs on both dusters and the truck, nice deep sound and no drone. Baffles will eventually burn out and things get louder but still no drone. The the dusters are both header to muffler, truck is factory pipes minus the cats to muffler
     
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