I did it. Eliminated the 2000 rpm exhaust drone - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-08-2009, 12:14 AM
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I did it. Eliminated the 2000 rpm exhaust drone

After changing the mufflers, changing to highway gears, adding another $300 of sound-proofing to the car, I still had too much exhaust noise inside the car.

There was no way of even dreaming about taking the beast on a long cruise down a winding highway without ear plugs!

Last weekend, I was running up a moderate highway hill and gave it a little gas. It was like being inside a drum!

I googled exhaust drone, and came up on a couple forum links (other sites) discussing exhaust drone at 2000 rpm.

Hey that's what I had.

Something about sound waves. The frequency of the engine exhaust and the length of the tail pipes, at 2000 rpm (or therabouts) causing a reverberation... yada yada.

The solution; teeing off a dead end tube on each tail pipe, which is about 50% the length of the tailpipe.

Hmmm- hocus pocus, or will it work.

I also looked at a couple links of BMW exhausts with a resonating chamber built in to the exhaust (attached below)

Okay that sold me. I was going to try it. If it did not work, what did I have to lose? Bonus, there is no exhaust restiction, no power penalty.
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Old 03-08-2009, 12:19 AM
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They call them resonators for a reason, try a set on each pipe...beats $300 worth of sound deadening anyday. The longer the better.
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Old 03-08-2009, 12:25 AM
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So here goes.

I tee'd both tail pipes. I had an extra pair of exhaust clamps and bought some stainless exhaust tips (cheaper than buying a length of s/s pipe)

A couple nights of welding, and it's done.

I made one tube 22" and one 26".
Sound waves are supposed to bounce back through the tubes and cancel the reverberation (drone)
Theory is differing lengths will cancel a different range of droning and tail pipes will act slightly differently.

So results;

Exhaust note is way quieter, maybe even too quiet for a hot rod.

Tested it throughout the rpm range. A lot quieter. It even sounds like a different car.

Okay the drone test.

Took it up a few hills thursday night. 4th gear, 3rd gear... loaded up at 1800-2200 rpm... no drone.

Today took it up the same freeway hill as the previous weekend. No drone. It's gone.

The way I built it, I could simply unclamp the tubes and cap the tee if I liked.

I located the tubes across in front of the fuel tank, where the traditional cross flow muffler would go on a mustang.

I am still getting a little rapping from the tri-y headers, and may try the summit collector screens. I think this is due to the header design.

Now I can listen to the radio and low volume on the highway.


A couple pics in the journal
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Old 03-08-2009, 11:48 AM
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http://en.wikipedia.org/wiki/Helmholtz_resonator

Nicely done there guy.
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Old 03-08-2009, 02:42 PM
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Funny, I removed the resonators from our 06 Charger R/T. I personally like the sound. To each his own, glad your happy with the results.
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Old 03-08-2009, 07:08 PM
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Okay heres a couple links from othe guys who tried this;

Newer mustangs

Pick up trucks

and I am not talking about loudness nor about inline resonators, which would be inserted within the exhaust flow.

This is all about the drone that occurs, usually when the engine is under load or partial load. This seems to happen about 2000 rpm on most V8's.
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Old 09-10-2009, 09:04 PM
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Update on the resonator tubes

I found that sometimes the beast was a little too civilized.

I decided to install electric cut outs on the exhaust resonator tubes that I made.

The result, at the flick of a switch I can be loud or quiet. It gives a good example of what these two tubes teed off the tailpipes actually do.

Video with electric cut outs

more explaination in the journal
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Old 09-11-2009, 12:01 AM
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Quote:
Originally Posted by Ripped
Okay heres a couple links from othe guys who tried this;

Newer mustangs

Pick up trucks

and I am not talking about loudness nor about inline resonators, which would be inserted within the exhaust flow.

This is all about the drone that occurs, usually when the engine is under load or partial load. This seems to happen about 2000 rpm on most V8's.
2275-2350 on my x piped straight piped Chevy
Shane
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Old 09-12-2009, 08:26 AM
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1800-2000 on my 96 Impala SS
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Old 09-12-2009, 09:46 AM
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Putting in an H-pipe right before the rear mufflers would had the same effect. That is, if there is room for the H-pipe. A rear mounted H-pipe works great on 70's vettes to stop that low rpm drone.

That same dead-end-tube trick is done with intake piping systems.

quiet powerful cars is the way to go. good job. It is never too quiet.
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Old 09-12-2009, 10:26 AM
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Quote:
Originally Posted by Ripped
The solution; teeing off a dead end tube on each tail pipe, which is about 50% the length of the tailpipe.
You will notice that many new cars have exactly this configuration on the inlet tract. Now you know why.
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Old 09-13-2009, 01:01 AM
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Lots of great information... Thanks guys.

I wish that I had this knowledge earlier on, I maybe would not have had to replace the 14" magnaflows with the 22" mufflers.

It would be fun to be able to vary the length of the resonator tubes to "tune" the exhaust note.

I notice now, with the collectors making a 4" tee on the tailpipes, before the electric cut offs, the exhaust has a very harmonic sounding note.
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