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  1. #1
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    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
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    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
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    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
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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
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    Curious too...

    Andrew
    1970 GTO Version 2.0
    1967 Cougar build
    GM High-Tech Performance feature
    My YouTube Channel Please Subscribe!
    Instagram @projectgattago

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

  6. #6
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    Oct 2014
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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
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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
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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
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    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 2.0
    1967 Cougar build
    GM High-Tech Performance feature
    My YouTube Channel Please Subscribe!
    Instagram @projectgattago

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

  10. #10
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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
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    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
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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
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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
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    That is a cool solution to your problem. I like it.

  15. #15
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    Cool, been waiting to see how the size you picked worked for your application.

  16. #16
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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
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    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
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    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
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    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
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    Are those vacuum actuators "tune-able" to open at a different point?

    Nick ~
    1969 Cutlass

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