NEED HELP Exhaust drone

hawkeye405

Silver Supporter
I just had a Magnaflow muffler installed and ran a straight pipe in place of the resonator into a "Y" tip. the drone was unbearable. I went back to the shop and had them install a Magnaflow resonator with the "Y" tip. It cut the drone down substantially but it's still there. It doesn't sound too loud until I hit 2k rpm which is around 70mph highway speed. Is there a way to eliminate the drone without changing the muffler?

What part of the exhaust does the drone come from? Would installing Dynamat on the floor reduce the drone?
 

HARDTRAILZ

Moderator
Which magnaflow? I have a 3 inch in and out version with a 3 inch dump off the back of the muffler and no drone. Or could it be the Y tip?
 

Mooseman

Moderator
Replacing the stock exhaust with anything aftermarket usually invites drone. It's caused by a certain resonance frequency that OEM's tune out with the muffler and specially tuned resonator.

Some people add an adjustable J-pipe to the exhaust to tune out a particular frequency. Some OEM's even have a J-pipe built in to their mufflers, which explains their huge square size.
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
 

Sparky

Moderator
J pipe is probably the way to go (or an oem muffler). Was going to do that on my truck but never got around to it as it hasn't bothered me enough.
 

HARDTRAILZ

Moderator
I did not have drone with my previous hooker exhaust either. Which was all the way out the rear side with a 3.5 inch tip.

I would try it without the Y tip before swapping muffler
 
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hawkeye405

hawkeye405

Silver Supporter
Thanks for the quick replies guys. I'm not sure which Magnaflow muffler he installed. I'll try and remove the "Y" tip and go with a straight pipe from the Magnaflow resonator. Should I go with a larger diameter chrome tail piece? If this doesn't work, I'll have to try the "J" pipe.

I also noticed a decrease in speed when going around 60mph at 2k rpm. If I try and maintain a steady speed at 60mph, I need to depress the accelerator or the truck starts slowing down. This began after I installed a CAI and the Exhaust. Any reason for this to happen?

Mooseman, I clicked on your link..... and several other links once there. Seems that there is so much discussion about this "drone" issue. People are saying that corsa is the best system out there and is designed to eliminate drone from inside the vehicle cabin. Then others' say that's not true and hate Corsa.

As for the "J" pipe, there doesn't seem to be a set dimmension of the pipes and the calculations just left me head spinning.:hopeless:

I was hoping someone had figured this out and replied with "do this". My 60 year old brain can't handle the drone or all the calculations but I love the sound of the my exhaust outside the truck.
 
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Mooseman

Moderator
CAI's are BS and a lot of times, are HAI's (Hot Air Intake) if not properly isolated from the engine heat.

The stock exhaust on these trucks are pretty free flowing. Only reason to replace it would be for the sound. I did that mistake. I installed a JBA Headers cat-back. It flowed great but sounded like a fat ricer, no matter what muffler I used.

Did you go with a 2.5" or 3" system. The stock system is 2.75".
 

MRRSM

Lifetime VIP Supporter
The "Intake Side" of Resonator Deletion can also add to this condition. The Air-Box Resonator functions well enough at around 2,000 RPM... to defeat the Sound Waves created by the Inward flow of the Air stream; literally Bouncing Off of the Piston Tops on their Inhalation Strokes.

In its absence... the Harmonic Sound Resonance can increase and create an audible, pulsed wave with enough amplitude to eventually disrupt the precise "Gram Weight" measurement of the Incoming Air stream through the MAF Sensor to make it fail.

Between the two sides of this event... 'The Motor In the Middle' can behave somewhat like a Pipe Organ. If you use this vehicle as a Daily Driver and cannot sort these problems out... you might become a Pariah to your Neighbors...or Go Deaf as a result of 'Unresolved Helmholtz Resonance'. This is a very good article on this topic:

https://itstillruns.com/air-intake-resonator-do-12156112.html

Here is the application of a Helmholtz Device on an Exhaust System to reduce that Dreadful Harmonic Drone Sound:

While I think this Dude's presentation is excellent... Instead of using the proper expression for LOUDNESS Levels as "Decibels"... he uses the expression "Herz" ...and his Metal Working and Shop Safety Skills need a some Tuning Up. Nonetheless... He covers the actual Technical Aspects with the Mathematics you need to know to get this Helmholtz Resonance Chamber Design doped out and constructed:


 
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SBUBandit

Well-Known Member
Where is the new exhaust exiting? If its not sticking out far enough where the sound coming out hits the inside of the back bumper it will echo around in there and drone pretty bad. My TB is starting a pretty good drone, but there is an off chance that that is the fact that the entire front end of the factory muffler is rusted completely off.
 

MRRSM

Lifetime VIP Supporter
The Helmholtz Device as an Add-On is NOT an additional mechanism to ease or accentuate the Exhaust Stream Path as in using a True Dual Exhaust System... Rather it is a "Counter-Echo Chamber" that counter-vibrates the Air trapped inside to neutralize the Harmonic Vibrations that oscillate only when the engine reaches a certain RPM Range... be it 1,500... 1,800...or 2,000 RPM... acting as a Passive Chamber ...cancelling out those ever-increasing oscillations created by the operation of the Engine... so they cannot amplify sound loud enough to become a problem.

There IS No Exit from this thing....and it's parallel presence alongside the Resonator Pipe does NOT disrupt the Exhaust Flow from the Stock Exhaust. As long as the Device is designed specifically for the RPM Range that is Triggering the Drone Sound that is happening uniquely in any particular vehicle... It will NOT Echo those vibrations and sounds... but it WILL serve to efficiently KILL them. That is How it Works. I agree with you that if your Muffler is compromised by Damage or Rust-Through... besides being excessively loud in ALL RPM Ranges... The Helmholtz Device will NOT work until a New Muffler gets installed and this Thing gets properly welded in place.

But... if you intend upon replacing the Damaged Muffler under your Vehicle with an OEM 'Stock as a Clock" Muffler-Resonator... you will NOT need to install either this ...or any other adaptation to control the sound of your exhaust. However... if you decide to venture into the Uncharted Regions of Aftermarket Exhaust Systems... you probably will need something like this Helmholtz Chamber ...to save your Sanity and your Hearing.

One last important observation. The Dude in the 1st Video describes "The Speed of Sound" as being 600 'Degrees'... but the actual measurement scale is in FPS (Feet Per Second)... which can vary as a function of your Altitude AND Air Pressure and Temperature. This requires using a Graph/Table or relevant Chart that you can fit into the overall Helmholtz Formula... depending upon whether you can look out of your window and appreciate the view of the Dead Sea (The Lowest Natural Elevation Point on the Planet) or when sitting in your SUV on top of Pike's Peak.

If you are going to get the most out of this Device... You should know that "The Speed of Sound" as a general, Baseline Rule... is always given by measuring its velocity through the Air at Sea Level with the ambient Air Pressure at 14.7 PSI making the SOS equal 1,116 FPS... roughly TWICE the measurement he mentioned incorrectly when performing this calculation.

And so ... you will need this linked Engineering Chart to examine your local conditions and take the correct data from it depending upon where you live ...and how high or low you are above or below in relation to the surface of any Level Sea near you on the Planet Earth:

https://www.engineeringtoolbox.com/elevation-speed-sound-air-d_1534.html

This next stuff gets ‘a bit technical’... but all of these articles are worthwhile reads to get grounded in the Math and Ideas involved.

This First Article… Has the BEST Explanations and Formula needed to create the measurements and calculations to figure out the Dimensions necessary to solve a particular Resonant Frequency Problem:

https://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture3 /ho_helmholtz/ho_helmholtz.html

This one covers Basic Muffler Design…

http://www.vaglinks.com/Docs/Misc/MufflerDesignConcept_Section3.pdf

...and from this White Paper… From Page 19 onward… Excellent Explanations...

https://preserve.lehigh.edu/cgi/viewcontent.cgi?article=2015&context=etd

… and here comes another White Paper discussing a “New Model” for the Muffler System on an IC Engine that is interesting as well…

https://springerplus.springeropen.com/track/pdf/10.1186/s40064-016-3060-1
 
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hawkeye405

hawkeye405

Silver Supporter
CAI's are BS and a lot of times, are HAI's (Hot Air Intake) if not properly isolated from the engine heat.

The stock exhaust on these trucks are pretty free flowing. Only reason to replace it would be for the sound. I did that mistake. I installed a JBA Headers cat-back. It flowed great but sounded like a fat ricer, no matter what muffler I used.

Did you go with a 2.5" or 3" system. The stock system is 2.75".

I just asked the guy at the custom exhaust place I went to to install a good sounding system. I'm not sure what size he installed or which Magnaflow model muffler either.

Where is the new exhaust exiting? If its not sticking out far enough where the sound coming out hits the inside of the back bumper it will echo around in there and drone pretty bad. My TB is starting a pretty good drone, but there is an off chance that that is the fact that the entire front end of the factory muffler is rusted completely off.
It comes out the rear just beyond the rear muffler.

1546711541835245899413583863355.jpg15467115795144362997104951059838.jpg


Thanks MRRSM
 

HARDTRAILZ

Moderator
That resonator in the picture is not the only muffler installed, is it?
 

HARDTRAILZ

Moderator
Could it be that resonator conflicting with the Magnaflow then?
 
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hawkeye405

hawkeye405

Silver Supporter
Actually no, the drone was much louder without the resonator. This is also a Magnaflow resonator. If my calculations are correct, I would need a 36" "J" pipe if I would go that way. I wonder if covering the floor with soundproofing material and foaming in the pillars would silence the drone?
 

MRRSM

Lifetime VIP Supporter
I'm kind of surprised that someone hasn't considered creating an "Adjustable Automotive Helmholtz" Device. Following on with the design suggested by the Dude in the 1st Video, all that would need to be added in and modified would be to create not (2) ...but (3) 4" Steel End Plates... with (1) bored out for the "J" Pipe Extension on one end... and the other (2) Plate being center-bored to accommodate a threaded 3/8" Steel Rod. The one playing the role of the Inner Piston would need to be slightly reduced in its OD to travel reliably down inside the inner length of the Helmholtz Tube. If there is enough room under the vehicle... you could also extend the 4" Tube Length to around 40" as well to ensure an adjustable length beyond the Basic Formula.

Prior to welding on (1) of the (2) 4" Plates onto the End of the Tube ... this OUTER End Plate would need a 3/8" NUT Welded over that small, centered hole in that End Plate and then have 24" X 3/8" Long Threaded Steel Rod wound inwards through it, far enough to pass it through the Center small 3/8" hole of the (2) Adjustable Interior 4" Plate. If you wanted some additional insurance (and assurance) that the Adjustable Inner Plate does NOT have any tendency to "Rattle & Vibrate"inside of the 4" Tube... you could use (2) separate sections of Inner Plates with some 1/2" to 1" thickness of Fiber-Glas Fabric laminated in between and smoothly secured on the OD of the two plates with some JB -Weld....making it even MORE robust.

After that, the 3/8" Rod and the Adjustable Inner Plate can be secured together using (2) 3/8" Nuts; one on either side of the 4" "Plunger Plate" to sandwich them together and stabilize it like a "Piston in a Cylinder". Then weld them both solidly in place. Last but not least... after feeding the Rod & Adjustable Plate into the inner length of the 4" Tube... the Back End Plate with the in-Dwelling threaded on Rod would need to be welded to close up the back end of the 4" Tube.

Once installed in the right location...In this manner... a whole range of Harmonic Reductions could be explored using the Rod to move the Adjustable Interior Plate either inwards or outwards (with a 9/16" Nut Welded to the Rod) and either tightened ...or loosened as needed with a Hand Held Drill. This way... you'd get to drive the vehicle around and have many 'oppor"TUNE" ities' to Dynamically Test the system out until you can locate the "Sweet Spot" that Quiets Down the Harmonics ... Just Right. If you decide later on to create what you discover as a New Unit... record the LENGTH of the Cut Off piece of 3/8" Rod ...so you'll know exactly How Long to make the 4" TUBE portion for the New Custom Unit.

Once that is achieved... The excess length of the Adjustment Rod could be cut off and the End Plate can be welded shut in the Center around the Rod. These Mild Steel Plates/Threaded Stock Steel Materials are ubiquitous and inexpensive... and would last as long as any other Mild Steel components already comprising the other stock exhaust system. I cannot think of a more flexible way to precisely "Tune Out The Drone". :>)
 
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hawkeye405

hawkeye405

Silver Supporter
MRRSM, that sounds like a great idea. How about a sketch? You know that old saying "a picture is worth a thousand words".

Not only do I hear this horrid harmonic drone, I also feel the floor under my feet vibrate. I never expected any of this at all. This system is already installed so I'm willing to try all I can to eliminate the drone.

Someone mentioned that the drone stopped when they drove over a steel bridge. So the sound must be bouncing off the pavement and going upward hitting the truck floor. That's what gives me the soundproofing idea. Filling the pillars between the doors with spray foam might also cut down on the echoing.

Any thoughts?
 

MRRSM

Lifetime VIP Supporter
People underestimate the Sheer Power of ANY System that tunes in on One Frequency Level ...with an Exponential Increase in Amplitude over time. Not to belabor your thread with more than is necessary... But THIS information is Dead Balls On Topic:

Back when Nicola Tesla was still alive ...and living off the Good Graces of his A/C Electricity Project Financiers, J.P. Morgan and George Westinghouse... he attached a small, Hand Held Amplifier of his own design to one of the Steel Girders down in the very bowels of his New York City Apartment Building to test out one of his Theories of Ever-Increasing Amplitude.

The device was simple enough... just a Mechanical Piston that tapped the Girder...rhythmically... again and again and AGAIN... at the precise Frequency and Time that caused the Steel Super-Structure to oscillate in time with the Infernal Device. Within a few hours... the Entire Skyscraper began to Shake and Shudder and Sway...and a VERY Shocked and Surprised Tesla made a Mad Dash down to the Basement to unstrap and remove the Damned Thing before the entire Building shook itself apart. THIS is NO "Bravo Sierra"...!

So if you decide to maintain that Dreaded Tuned RPM for extended periods of time... besides shaking the spot welds apart inside of your SUV and loosening your Eye Teeth over time... well... since you mentioned the phenomena someone experienced when "Driving over a Bridge"... Let's watch what happens when a persistent 40 MPH Wind found the "Drone Frequency" of THIS Bridge... and you'll understand that Insulating the Floor Boards or packing the Body panels and Uprights of your Vehicle with Plastic Foam... Will NOT Stop this Problem.

I'll draft up a simple Design Diagram for the Adjustable Helmholtz Device very soon ...with a Parts List that coincide with my wordy description above. Trust me, Brother... We ALL want you to Defeat this damned problem! Now Grab your Popcorn and a Soda... then sit back and watch what happens to "Poor Gertie":

 
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MRRSM

Lifetime VIP Supporter
Okay… Hopefully… These highlighted images will give you enough of an idea of “How to Build an Adjustable Helmholtz Resonator Tube”. Here is the Legend and Component Information:

(1) The 10 MM X 1.50 MM Threaded Rod is what does the Moving… inwards and outwards through the Two Welded on Metric Nuts on either side of the Back Plate. Do NOT Weld The Rod to That Plate! You can quickly make adjustment under the Vehicle if you Weld a 10 MM Nut on the Very End of the Exterior of that Threaded Rod.

(2) The Front Plate in the attached images is 4” in Diameter to Scale and has a Hole Center Drilled to allow for a “J” Pipe Insertion… (Two “Yellow Plastic” Plates I'm using represent REAL Metal End Plates used in this Example). Both Plates eventually MUST be Welded at their Outer Edges to the ends of a 4” X 40” Steel Pipe.

(3) All Imaged Fasteners (M10 X 1.50) showing Sky BLUE DOTS MUST be Welded to the THREADED ROD.

(4) All Imaged Fasteners (M10 X 1.50 showing RED DOTS MUST be Welded to the BACK PLATE.

(5) The In-Out Arrows define the Freedom of Movement allowed by the Threaded Rod.

(6) The Black Plastic Plate is what MOVES inside of the Hollow 4” X 40” Length of Pipe. It gets Fixed and Welded to the Very End of the Adjustable 10 MM X 1.50MM Rod with opposite facing Flange Nuts for Stability.

(7) I did NOT have a 4” Pipe available to install all of this Example Gear into… so You’ll just have to use your Imagination.

(8) I would suggest using a thicker piece of 3/16” X 6” piece of Mild Steel Plate to cut out the Adjustable (Black Plastic) Plate as its thickness will be better for stability on the end of the Threaded Shaft and naturally… its OD will have to be ground down to be SLIGHTLY Smaller than the Inside Diameter of the 4” Steel Pipe. Make certain that the Adjustable Steel Plate travels easily into and out of the length inside of that 4" Steel Tube.

(9) Remember… It’s the Two “Yellow Plates” that get Welded to the Front and Back Ends of the 4” X 40” Hollow Steel Tube… NOT That Black One!

(10) Do NOT Start Welding until all of these components are Pre-Fitted and Double Checked for their Positions and Follow the Orders of Assembly. Triple Check Yourself B4 Firing Up The Welder! Do NOT Use or Weld Chrome Plated Fasteners as they will produce Toxic Halides and Chromate Gases that can KILL YOU if you accidentally breath in those Vapors!


ADJUSTABLEHELMHOLTZ1.jpgADJUSTABLEHELMHOLTZ2.jpegADJUSTABLEHELMHOLTZ3.jpegADJUSTABLEHELMHOLTZ4.jpegADJUSTABLEHELMHOLTZ5.jpegADJUSTABLEHELMHOLTZ6.jpegADJUSTABLEHELMHOLTZ7.jpegADJUSTABLEHELMHOLTZ8.jpeg
 
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Mooseman

Moderator
Geebus Bob, I thought you were gonna show something simple!

This is what I've seen on Caprice/G8 forums from Solo Performance and could easily be replicated and added to your system.



The only thing to figure out is the length to the middle for your particular frequency you're trying to eliminate. Note that it doesn't have to be a J pipe. It could just be a Y or T pipe like this:



That's if you have room for a straight one. The advantage of the straight one is that it could be infinitely adjustable using two pipes inside each other with the end capped.

If you Google for images of adjustable exhaust J pipe, you'll find lots of examples.
 

Sparky

Moderator
I was going to say, why not just a capped pipe that slides inside another pipe and use a simple exhaust clamp to hold the adjustment?
 

MRRSM

Lifetime VIP Supporter
Actually... While I really do like ALL of your Ideas you both mentioned... I was simply responding to the request by the OP by applying what I read in the White Papers listed previously. The Paper describes that some adjustments in the length of the "J" Pipe were more particular to the OD Sizing of it ... rather than to its length. When the subject of the LENGTH came up later into that review in their study... The Length of that Tube...as well as the Narrowing of it towards the Back Plate seemed to add in some additional flexibility in Secondary Harmonic Frequencies being brought under control that it would handle them as well much better.

Also ...To some extent... the general Pitch of the overall Sound emanating from the Tail Pipe was also affected. The only other thing I would add in to the Hardware Design I suggested... is to include a 10MM X1.50 Locking Nut on the exterior length of The Threaded Rod to be able to secure that Rod to the Outside of the Back Plate after making many necessary experimental adjustments.

My design is probably NOT the Best Choice... but it does compliment the design of the stuff covered by the VOP in the 1st Video. I also think that it creates a greater range of discovering the problematic RPM that has been serving as the precise Trigger Point. In any case... The More Ideas available for making the right choice... The Better. You know me... if I have to Engineer anything... it has to Work Right and be Durable... Right Out of The Box... and that does not always translate into simplicity and elegance others with a better understanding manage to design into their hardware accordingly.

@Sparky's idea makes perfect sense to me with the notion of Telescoping One Tube inside of Another. The only problem I can see though is that making adjustments to it that will not leak or slip vs. the very direct method of either tightening or loosening that One Threaded Rod in finely measurable increments without many complications seems easier on my 'Instinctive Engineering' of the Helmholtz Device. Again... I appreciate everyone making their thoughts known and offering some very clever, if not better ways to go about doing this than my own.
 
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hawkeye405

hawkeye405

Silver Supporter
This us really getting close to solving my issue. Like I said before, I want to keep this muffler and resonator. I've received many many compliments on the sound of this system on the exterior. I will take a close look at your design MRRSM. I'll need to figure out a way to explain this to my Hispanic muffler guy. Mooseman, your sketch will help with the translation. One question though, are the black Mark's holes drilled into the pipe?

What a great way to spend my Friday night.....a glass of brandy and reading this post.
 

Mooseman

Moderator
No holes. I think they were just manufacturing marks from bending the pipe. It's a completely closed and capped pipe.

PS: Thanks for becoming a supporter! :thankyou:
 

MRRSM

Lifetime VIP Supporter
Hawkeye...

I copied the Line Diagram provided by @Mooseman and added-edited in the Red Lines to show you (and Your Hispanic Muffler Mechanic) where the apparatus I described with Photos can be installed into the "Branch Resonator" noted thereon:

ADJUSTABLEHELMHOLTZ2.jpg
 

MRRSM

Lifetime VIP Supporter
The MUFFLER is not shown in @Mooseman's Diagram... but it would be installed at the BOTTOM of the Diagram. This assumes that you follow a normal layout IN THIS ORDER:

(1) The Exhaust Manifold
(2) The Catalytic Converter
(3) The Resonator ...WITH THE SUB-PIPED-IN HELMHOLTZ DEVICE & ADJUSTER ATTACHED
(4) The Long Exhaust Pipe to the Back of the Vehicle
(5) The Muffler
(6) The Short Pipe Guiding the Muffler Exhaust out the Rear of the Vehicle
 
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HARDTRAILZ

Moderator
Normal layout is the resonator at the end.

Manifold/Cat/Muffler/Pipe/Resonator with tip exiting under rear bumper

That is typical for these.

I do not think you could even fit a stock sized muffler under the rear after axle without it sticking out since they are so large on these.
 
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hawkeye405

hawkeye405

Silver Supporter
That's what I was trying to figure out. Since the muffler installer was willing to replace the Magnaflow muffler under warranty for free, I decided to go that route. I still have the Magnaflow resonator and Y tol. The sound is still good but no drone inside the truck. It's not silent but I like it. Looks like he changed the pipes from the cat back to the Y tol to 3.5" too.

I truly appreciate all of your replies guys.
 

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