Branch resonators - ways of reducing exhaust drone

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Kristian_Wraae

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I'm looking for information on the use of branch resonators in order to reduce drone.

Has anyone used branch resonators? Any information? Links?

What I'm intersted in is where exactly to put them and how to determine the size (length/diameter).
 
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Kristian_Wraae

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I have read that link before I posted but I can't figure out if it matters where the resonator is welded to the exhaust. Also when I try to calculate the length of piping needed it turns out to something like 2 meters due to the fact that our inline six cylinder engine fires like a 3 cylinder engine.

I don't see why it would mess with exhaust flow - no exhaust is flowing in the resonator - only sound waves.
 
tissimo

tissimo

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On my old 2jz car, I had a regular summit glass pack resonator with an apexi N1 canister and there was nearly no drone. The car was fairly quiet at idle/cruising (couldn't hear it inside with windows up a/c on and radio on low volume at 70 mph).
 
deabionni

deabionni

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Sep 16, 2007
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Our BMW 540i has a resonator that has a branch running off of it.

*Not my pic, but you get the idea*
540exhaust.jpg


To make something like that in a Supra, you'd just need to make the branch in front of the rear diff, and have it come around the diff on the other side of the rear subframe.
 
gofastgeorge

gofastgeorge

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HKS puts them right before the mufflers.

Sometimes just the placement of the muffler in the system will effect drone.
On an old Corona I owned years ago (first Toyota),
I had installed a full 2.5" systems with a 'turbo' muffler.
It was terrible at 60mph!
My teeth would vibrate.
Below 50, and above 65, there was no drone.

I moved the muffler from behind the rear axle, to the original location
(about a foot ahead of the rear axle)
and the drone went away.

So it all depends on the system, and how that particular system sets up resonance.
sm_photo_missing.jpg
 
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Kristian_Wraae

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Ok, I'm trying to figure out the length of the pipe to use for a branch resonator.

I use this calculator to calculate the wave length:

http://www.autolounge.net/calculators/exhaust/exhaustresonance.html

I assume I need to input the number of cylinders. The 7mgte engine fires two cylinders at the time, so I guess our 6 cylinder engine transforms to a 3 cylinder engine, right?

If I get drone at 2000 rpm the standing wave length is: 11 feet.

So I read this:

SidebranchResonator.jpg


http://www.enoisecontrol.com/related_articles/engine_exhaust_sound_control_barrier_wall.pdf

at page 44 there is a formula for the length of the branch resonator. It says lambda/4 where I assume that lambda is supposed to be the wave length of the standing wave which is what causes the drone.

So 11 feet / 4 = 2.75 feet = 82.5 cm

The side branch resonator should be the same diameter of the rest of the exhaust (in my case 4 inch).

So I need 2.75 feet of 4 inch pipe welded to the exhaust right before the last muffler to reduce drone with 20 - 30 db, right?
 
87M-GTE

87M-GTE

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Drone is a myth... I have a full 3" turbo back, no cat with a Blitz Nur spec and It its honestly not that loud until under boost or heavy throttle, even then its not all that loud.
 
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Kristian_Wraae

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87M-GTE;1365357 said:
Drone is a myth... I have a full 3" turbo back, no cat with a Blitz Nur spec and It its honestly not that loud until under boost or heavy throttle, even then its not all that loud.
Click to expand...

As Poodles says drone and loud exhaust are two different things.

My 4 inch system is not loud at all.

But around 2000 rpm the entire car shakes. The dash is rattling and rear view mirror is shaking.

Around 3000 rpm and above all is fine and not loud.

So I need to remove this resonance which is around 2000 rpm.

As far as I can see a branch resonator will do exactly that.Just need to figure out the sizing and placing.
 
3p141592654

3p141592654

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Oct 11, 2005
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You could get away with smaller diameter piping for the stub pipe. The diameter changes the characteristic impedance of the stub, which ideally you would want to be the same as the other pipe. The smaller stub will not cancel quite as well, but will still make a good improvement. For any electronic microwave circuit designers out there, this is a transmission line notch filter.
 
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Kristian_Wraae

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3p141592654;1365427 said:
You could get away with smaller diameter piping for the stub pipe. The diameter changes the characteristic impedance of the stub, which ideally you would want to be the same as the other pipe. The smaller stub will not cancel quite as well, but will still make a good improvement. For any electronic microwave circuit designers out there, this is a transmission line notch filter.
Click to expand...


With stub pipe do you mean the entire branch or just a smaller diameter connection between the branch pipe and the main pipe?

Any downside to keeping it 4 inch all the way in the branch? I would like maximum dampening of the resonance.

Does the branch need to be a 90 degrees to the main pipe or would other angles be better? (say 135 or 45)

Would it be better to put the pipe as close to the end muffler as possible? Or should it go in the middle? Or close to the downpipe?

Will placing the branch at either of the aforementioned three places need different angles? (ie maybe close the the end muffler and poiting the entrance forward like and the branch backwards in a "Y" at 135 degrees?)
 
isnms

isnms

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Kristian_Wraae;1365370 said:
But around 2000 rpm the entire car shakes. The dash is rattling and rear view mirror is shaking.

Around 3000 rpm and above all is fine and not loud.
Click to expand...

Make sure your exhaust pipe is not touching anything.

When I installed my Raptor 3" cat back it was touching the transmission support. At around 2000 rpm my dash would shake and vibrations heard all around. Above that it was fine. I removed the little bit of the support that was touching and no more vibrations.
 
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Kristian_Wraae

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I don't think it is touching but I will check again. It is not bolted to the stock support bracket for the downpipe at the moment because we were out of 4 inch clamps. So the exaust is hanging in the turbo and in the rear mounts only.

There is of course a slight chance that movement from engine moving during acceleration will push the downpipe towards the transmission mount.

I still think it is droning, but good point though.
 
gofastgeorge

gofastgeorge

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Kristian_Wraae;1365307 said:
The 7mgte engine fires two cylinders at the time, so I guess our 6 cylinder engine transforms to a 3 cylinder engine, right?
Click to expand...


No, not quite........
4-cycle engines fire every 2 revolutions.

Yes, 2 pistons come to top dead center at a time, but only one is on the fire cycle,
the other is inbetween exhaust, and intake cycles.
 
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Kristian_Wraae

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gofastgeorge;1365475 said:
No, not quite........
4-cycle engines fire every 2 revolutions.

Yes, 2 pistons come to top dead center at a time, but only one is on the fire cycle,
the other is inbetween exhaust, and intake cycles.
Click to expand...

Ahh, ok so it does fire like a 6 cylinders?

Good news. Means that the pipe will only need to be half the length.

So only 41.5 cm. Much easier to fit.
 
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