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    1. #1
      Join Date
      Oct 2014
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      DFW, Texas
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      422
      Country Flag: United States

      Have you used Helmholtz Resonators? Exhaust Drone

      I have a moderate 2,000rpm drone that I'd like to get rid of. Calculations to cancel 1/4 of the wavelength at that frequency (133Hz) looks to come right around 24".

      While packaging 24" resonators along the side of my 3" exhaust won't be easy, I think I'd like to try it.


      Have you used these style resonators before? What was your end result?
      Click image for larger version. 

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      Supporting info

      J-tube Vendor
      http://synapseengineering.com/synaps...3eb26nmm54fu62

      Synapes installation
      http://synapseengineering.com/suppor...ons_111513.pdf

      Grassroots thread
      https://grassrootsmotorsports.com/fo.../129212/page1/

      Calculation details
      https://www.performancetrucks.net/fo...-drone-489463/
      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    2. #2
      Join Date
      Sep 2004
      Location
      Orlando, FL
      Posts
      1,074
      Country Flag: United States
      Very interesting! Following... and wondering if you couldn't also put cut-outs on the ends of the resonators... hmmmm.
      SMSgt Ty Ingle, USAF
      "CF71" - Freedom Bird
      Hoodpins.com, Inland Empire Driveline, Billet Accessories Direct, Modo Innovations, AutoRad Radiators, Morris Classic Concepts, Marquez Design, Anvil Auto, Fesler Billet, US Collision (DOOM), AGR Performance, Pro-touringF-body.com, Phoenix Transmission Products, Shiftworks, ACC Carpet, Hedman Hedders, BMR Fabrication, American Autowire, MityMounts, TIN INDIAN Performance, Kauffman Racing Equipment, Pypes, RobbMc Performance, WMC, Holley, NOS, PST

    3. #3
      Join Date
      Jun 2012
      Location
      South Lyon, MI
      Posts
      1,217
      Country Flag: United States
      I've used them in fuel injection lines to reduce noise producing pulsations. If tuned properly, they can dampen out unwanted frequencies. The problem is that they only work in certain frequencies.

      I would be interested to see how they work in an exhaust system.

    4. #4
      Join Date
      Aug 2008
      Location
      jacksonville,fl
      Posts
      970
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      The math part of this I don't as of now have a grasp on, but I do understand how and that it does work.
      As mentioned with fuel, your average house water system usually has a set somewhere, usually near the washer. Pipes can clank, moan, etc at certain flow levels without them.
      Helmholtz resonator is an awfully fancied up word for a j-pipe with the end capped off. Only sound bounces in & out of the dead air space, not airflow, so no restriction. Just a few pounds of extra pipe would be only performance negative whatsoever.

      Do they work? Crack open a large ass late model muffler, such as 5th gen camaro's where I first heard of them. There are a lot of older threads on the J-pipe subject on forums like camaro 5. There are also aftermarket companies such as Solo selling basically muffler bypasses with a properly sized & located J-pipe so the exhaust can be loud in a good way & not buzz your brains out in overdrive. So, not a bs thing, just need the right size & location. Some setups telescopically adjust a little bit on length.
      Definitely on my to do exhaust list of still needed once I finally redo my setup. Been under our noses for years , just didn't know it as it's still not a fully understood subject.
      https://www.google.com/search?rlz=1C...w=1366&bih=625

    5. #5
      Join Date
      Apr 2001
      Location
      The City of Fountains
      Posts
      15,971
      Country Flag: United States
      Curious too...

      Andrew
      1970 GTO Version 3.0
      1967 Cougar build
      GM High-Tech Performance feature
      My YouTube Channel Please Subscribe!
      Instagram @projectgattago
      Dr. EFI
      I deliver what EFI promises.
      Remote Holley EFI tuning.
      Please get in touch if I can be of service.

      "You were the gun, your voice was the trigger, your bravery was the barrel, your eyes were the bullets." ~ Her

    6. #6
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
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      Just a quick update.

      I have ordered 2"x24" NoDrone helmholtz resonators to install before my mufflers on the 'Cuda. They're the longest I think I can fit back there.

      I also ordered two vacuum-actuated 2" exhaust cutouts that'll put at the end of the resonator, instead of the welded cap. In theory, I'll have open cutouts at ~70% engine load and closed/drone-less everywhere else. Should be fun!
      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    7. #7
      Join Date
      Aug 2008
      Location
      jacksonville,fl
      Posts
      970
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      I thought about possibly doing something similar later on. My current exhaust has a large oval 3.5" exit after my x-pipe going to a manual operated cutout & piped to a custom side exit pipe. It pretty much turns the x into a y when open & kills the tone an x -pipe gives. So I think the next version could be a twin setup off of j-pipes like you're doing , but with side exit pipes after cutouts. Nascar style boom tube exits could be cool.
      Now the only thing with having a cutout after the J is that if it leaks ,it could ruin some of the effect.
      In past research into j-pipes , a lot of people mentioned the dual purpose idea of a cutout at the end, but haven't seen one done yet. Someone needs to be the first.

    8. #8
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
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      Quote Originally Posted by jlcustomz View Post
      I thought about possibly doing something similar later on. My current exhaust has a large oval 3.5" exit after my x-pipe going to a manual operated cutout & piped to a custom side exit pipe. It pretty much turns the x into a y when open & kills the tone an x -pipe gives. So I think the next version could be a twin setup off of j-pipes like you're doing , but with side exit pipes after cutouts. Nascar style boom tube exits could be cool.
      Now the only thing with having a cutout after the J is that if it leaks ,it could ruin some of the effect.
      In past research into j-pipes , a lot of people mentioned the dual purpose idea of a cutout at the end, but haven't seen one done yet. Someone needs to be the first.
      My resonators will be after the H-pipe, we'll see how that works out, it shouldn't affect scavenging much.

      I should have a shot at getting it all installed in about 2 weeks. My car has rear exit exhaust out through the middle of the factory valance, this one would look a little goofy with side pipes, so the cutouts will just dump under the car.

      - - - Updated - - -

      Vacuum Cutouts, for reference

      https://proflowexhaust.com/products/...t-cutout-valve
      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    9. #9
      Join Date
      Apr 2001
      Location
      The City of Fountains
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      15,971
      Country Flag: United States
      Looking forward to the results. My exhaust pipes are pretty straight and basic. I can easily fit a 24" pipe between my manifolds and the mufflers. I don't have a drone now, but seem to get a more raspy exhaust note as engine RPM goes above 2200-2300 RPM....I wonder if this will fix that. Any thoughts?

      Andrew
      1970 GTO Version 3.0
      1967 Cougar build
      GM High-Tech Performance feature
      My YouTube Channel Please Subscribe!
      Instagram @projectgattago
      Dr. EFI
      I deliver what EFI promises.
      Remote Holley EFI tuning.
      Please get in touch if I can be of service.

      "You were the gun, your voice was the trigger, your bravery was the barrel, your eyes were the bullets." ~ Her

    10. #10
      Join Date
      Aug 2008
      Location
      jacksonville,fl
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      970
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      Could possibly make a difference with the correct length. They are said to reduce decal popping for many.
      Like I first said , I don't yet really understand all these formula stuff & tuning to the 4th pulse, 2nd resonance type crap, but there are formulas others use. What I don't trust about trying to use some types of formulas is knowing if you're really calculating the right way. From what I just read on one site, calculations may affect the rpm range +/- 400 rpm of the target range. I've seen pipe sizes on systems both bigger & smaller than exhaust. Seen some before mufflers & some after, so location may not be super critical. ALOT run no muffler, which some may have cats & or front resonators still in place.
      Unless someone can just copy someone else's exact system, then experimenting may be needed.
      So Andrew, you may try a formula figuring for2200rpm.
      Here's a link to some formula's on a challenger forum &Just a search link for solo perf, which makes a lot of systems with these J-bends.
      https://www.challengertalk.com/forum...34/index3.html
      https://www.google.com/search?q=solo...&bih=625&dpr=1
      I remember seeing other formulas out there.
      https://ls1tech.com/forums/cadillac-...ltz-tubes.html

    11. #11
      Join Date
      Feb 2013
      Posts
      799
      Country Flag: United States
      Why not just cap the J pipe with a closed-end, expanded pipe and exhaust clamp so you can tune the frequency on your car? Should easily be able to add 6 inches of adjustment that way.

    12. #12
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
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      Had some parts show up. I have 45° bends to include to help point the cutout away from the muffler and body, that'll add a little length to the system.

      Going to try to install this coming weekend.

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      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    13. #13
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
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      Installed these today as shown.

      Quick ride home tells me that my 2,000rpm resonance problem is greatly improved. The cutouts are working well they start to open up just a hair too early for my liking when i'm accelerating, I might be able to tweak that out some.

      Overall, this seems worth the effort. I have 3 hours of highway driving coming up this weekend, I'll get a better evaluation on it then.

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      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    14. #14
      Join Date
      Jun 2012
      Location
      South Lyon, MI
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      That is a cool solution to your problem. I like it.



    15. #15
      Join Date
      Aug 2008
      Location
      jacksonville,fl
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      970
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      Cool, been waiting to see how the size you picked worked for your application.

    16. #16
      Join Date
      Sep 2004
      Location
      Orlando, FL
      Posts
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      Can wait to hear how these sound and get your feedback after your long drive this weekend!
      SMSgt Ty Ingle, USAF
      "CF71" - Freedom Bird
      Hoodpins.com, Inland Empire Driveline, Billet Accessories Direct, Modo Innovations, AutoRad Radiators, Morris Classic Concepts, Marquez Design, Anvil Auto, Fesler Billet, US Collision (DOOM), AGR Performance, Pro-touringF-body.com, Phoenix Transmission Products, Shiftworks, ACC Carpet, Hedman Hedders, BMR Fabrication, American Autowire, MityMounts, TIN INDIAN Performance, Kauffman Racing Equipment, Pypes, RobbMc Performance, WMC, Holley, NOS, PST

    17. #17
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
      Country Flag: United States
      Quick video

      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    18. #18
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
      Country Flag: United States
      I put down 400 miles or so of driving this weekend and can say that my light cruise resonance has been resolved. The familiar drone does start to come back when I add load to the engine but no change in rpm [pulling a hill]. I find that a bit interesting because that's certainly not part of any of the calculations or reference material I looked at.

      Nevertheless, I am happy with the results. The 2000rpm cruising drone is gone!
      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    19. #19
      Join Date
      Aug 2008
      Location
      jacksonville,fl
      Posts
      970
      Country Flag: United States
      Cool. With some things close enough can be awesome. I'm sure you can't find any negative results, other than a little time & money.

    20. #20
      Join Date
      Feb 2007
      Location
      Tinley Park, IL
      Posts
      1,163
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      Are those vacuum actuators "tune-able" to open at a different point?

      Nick ~
      1969 Cutlass

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