Have you used Helmholtz Resonators? Exhaust Drone

[GoodysGotaCuda]

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?
164824

Supporting info

J-tube Vendor
http://synapseengineering.com/synapseusa/products/nodrone.html?SID=ofknrghqnqj63eb26nmm54fu62

Synapes installation
http://synapseengineering.com/support/faq/pdf/NoDrone_Installation_Instructions_111513.pdf

Grassroots thread
https://grassrootsmotorsports.com/forum/grm/problem-exhaust-drone-solution-side-branch-aka-14-wave-resonator-or-helmholtz-resonator/129212/page1/

Calculation details
https://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/

[OLDFLM]

Very interesting! Following... and wondering if you couldn't also put cut-outs on the ends of the resonators... hmmmm.

[cornfedbill]

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.

[jlcustomz]

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=1C1SQJL_enUS808US808&q=j+pipe+exhaust+explained&tbm=isch&source=univ&sa=X&ved=2ahUKEwjKq7WA7dXiAhXG1lkKHWkUAbEQsAR6BAgAEAE&biw=1366&bih=625

[andrewb70]

Curious too...

Andrew

[GoodysGotaCuda]

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!

[jlcustomz]

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.:idea:
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.:git:

[GoodysGotaCuda]

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.:idea:
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.:git:

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/proflow-vacuum-actuated-exhaust-cutout-valve

[andrewb70]

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

[jlcustomz]

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/forums/f18/j-pipes-eliminating-drone-354834/index3.html
https://www.google.com/search?q=solo+performance+j+pipe&rlz=1C1SQJL_enUS808US808&source=lnms&sa=X&ved=0ahUKEwiMwOfniqfjAhWhzVkKHQnmAZoQ_AUICygA&biw=1366&bih=625&dpr=1
I remember seeing other formulas out there.
https://ls1tech.com/forums/cadillac-cts-v-2004-2007-gen-i/1629371-cure-drone-1-4-resonance-pipes-aka-j-pipes-aka-helmholtz-tubes.html

[JustJohn]

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.

[GoodysGotaCuda]

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.

165759

[GoodysGotaCuda]

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.

166326

[cornfedbill]

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

[jlcustomz]

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

[OLDFLM]

Can wait to hear how these sound and get your feedback after your long drive this weekend!

[GoodysGotaCuda]

Quick video


https://youtu.be/2ARcqRhJHOI

[GoodysGotaCuda]

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!

[jlcustomz]

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.

[Mr Nick]

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

[GoodysGotaCuda]

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

No sir. Wish there was some adjustment there.

[jlcustomz]

I have zero experience with vacuum actuated exhaust valves, but here's a few thoughts::::
An example would be on older GM ac/ heat systems you had a large ball which was a vacuum reserve. Maybe some sort of small canister(adjustable size would be nice) that would save just a little vacuum to make them seem less sensitive.
Probably the only way the valve could be made tunable would be to restrict it , which I think would just make it close slower. Not sure if restriction would make it also open slower??? To have the opposite effect, you'd need to add vacuum.
I'm pretty sure the average vacuum canister consists of whatever air volume it offers & a check valve to not let vacuum bleed back out to manifold source. Based on that thought, maybe a canister with it's check valve could be installed inline ( Parallel ) with the main feed to offer some effect of momentary continued vacuum as the cannister bleeds down.
Another much simpler possibility of adjustment would be a tiny pull spring hooked up to the valves to help them in the stay closed direction, thus effectively retarding the vacuum drop effect.
Just a dumb thought from a high school only educated idiot that thinks more than sleeps.:lmao:

Anybody got any better ideas? Bill?

[GoodysGotaCuda]

So far I’m going to drive it as is and see how the valves hold up before getting too fancy.

I may install a boost controller valve to help manage the cutout. I can switch it to allow them to always be open, and I think I can get it to run a check valve and keep the valves closed. They don’t really bleed off on their own.

[jlcustomz]

Honestly I think that sort of setup would be more useful, being able to be fully open or fully closed when you want. There are plenty of times when you want to dip into throttle without drawing excessive attention or have that loud idle. I'll probably build me a better cable operated valve on my next exhaust.

[Mr Nick]

I was thinking there may be a simple adjustment to have them open at different vacuum signals, similar to a vac advance canister on a distributor. The KISS method may be a spring to delay/slow the opening points, like jlkustomz mentioned.

With a little tinkering, one could have a Helmholtz chamber and an active exhaust for far less than this kit, albeit with much less adjust-ability as well. https://www.holley.com/products/exhaust/exhaust_systems/hooker_blackheart/multi-mode_exhaust_kits_and_accessories/parts/71013001-RHKR

[rohrt]

I changed mufflers from a straight through design to a the super turbos, this reduced the drone but still there. Then i moved to the VT mufflers. Sad that they are a thing of the past now, because they worked great for me.

[BrianP]

Here’s a great YouTube video explaining the Helmholtz resonator. It has links to a nice spreadsheet to help calculate your size requirements.
https://youtu.be/z5SY5oUTEcc

[crash520]

Thanks Goody, I’m trying to resolve a 50mph drone, I’ve tried different mufflers, H pipe and X pipe and I currently have the Magnaflow system I had on my Cuda that had absolutely no drone at all, same system on my my 67 it drones like a B******, only difference is the 67 has factory performance manifolds, the cuda had TTI headers, so right now I’m looking at installing resonators in the engine pipes ahead of the X pipe ��*♂️

[mikedc]

Waking up an old thread here.

GoodysGotaCuda, I have a few questions.


Do you have any estimations about how much it reduces the drone? I'm guessing a couple decibels, which is noticeable, but not enough to make a passenger ask what just happened.

How wide of an RPM range does it work over? I'm assuming the effect shows up gradually as the tach gets near the 2000-RPM target and then fades as the tach climbs past it. Do you notice the 'dip' in the sound when you're running through the gears hard?

Do those cutouts open the exhaust entirely (pre-mufflers)? Have they proven to be reliable?

Any other thoughts on this mod?