2nd Gen Non-Engine/Transmission Exhaust Drone cured - well almost

[tmccormick]

So Gary. where you the one that posted this little trick over at Diesel Resorce?



You get ALL the credit for this tid bit.

 

[Gary - K7GLD]

YUP - I'm the guy...

 

[tmccormick]

I thought so... . just wasn't sure because it's been a while

 

[RT66DOC]

I agree with Gary about the guitar string analogy.



Another tidbit to keep in mind from an acoustic standpoint - having not much to do with the drone - is that moving the muffler forward tends to decrease low frequency sound waves in the system whereas moving it as far back as possible decreases high freqs. End result being deeper tone with muffler toward the rear. It's the high freqs that are annoying.



Where's the guy that designed the Mustang exhaust when we need him? Or maybe we should look at some 12 cyl. Ferrari exhaust systems - 2 x 6 = 12 so harmonics should be the same. Most Ferraris sound pretty good, no? Oo.

 

[JimKing]

Originally posted by Gary

Might not LOOK elegant, or solve ALL vibration/drone problems, but sure fixed MINE!



Yeah, but it works. I made some clamps like yours pictured, from 3/8 all thread and 1/2X1" flat bar. Works great and doesn't loosen up and rattle. Thanks for the pictures. . Today I am going on a test run up Copper Canyon, 6-8% grade, AND I am taking 2 cups of coffee.

 

[HEYBOSS]

Originally posted by Gary - KJ6Q

I think it's a characteristic more peculiar to an inline 6 - firing pulses are farther apart, and when the turbo spools, camshaft kicks in, BIG things really start happening under the hood...



The same jackhammer firing impulses are supposedly also responsible for other stresses throughout the drivetrain, especially the transmissions...



V8 firing impulses are closer together, and resonant frequencies apparently far enough off that it hasn't seemed to be a problem at the same level as the Cummins...

Yeah... ... ... ... ... ... ... but how do we get two identical trucks, same year, drive train except the color and one drones like no tomorrow and the other is absolutely drone free? That I don't understand? Before I ordered my truck, I road tested three identical trucks the dealer had on the lot and they all had a drone. When mine arrived and I drove it, it had the drone. Not bad stock but when you move up to 4" exhaust, it will drive you nuts. When I got involved in the TDR club, I've driven two other members trucks, same year, QC auto and same gear as mine and they are completely drone free!

 

[jandtjil]

Muffler bearings

 

[Mike Ellis]

Gary is right on the nose with the resonance cure.



The pipe hanging from its supports will indeed resonate at certain frequencies. Resonance can be induced from several mechanisms in such a system - the vibration from engine firing pulses, mechanical vibration coupled from the rest of the vehicle structure, expansion of the gases in the various sections of the pipe, etc.



Remember the old jug band "blow over the top of a bottle" routine? The exhaust system exhibits the same kind of standing wave resonance, just like a set of headers it can be "tuned" by varying the length / diameter / rigidity of different sections. Like an organ pipe basically.



The guitar string is also a good analogy, as far as understanding why some fixes help and others may not seem to. If you play guitar, you have no doubt encountered the technique of playing harmonics or "chimes" by touching the string at a certain point and plucking it as normal, even with the finger touching the string you can get it to sound. These points are at the nodes where the string is not vibrating - touch it anywhere else and it stops the vibration. Depending on where you attach your exhaust hangers, clamps, and angle iron you may see some effect on the resonance... or not.



In general, you can shift resonances to higher frequencies by adding mass to the system - like the angle iron, or by adding rubber hangers to isolate the vibration from the truck. Could probably do just as effective a job by putting a heavy "donut" in a few locations, like a couple of feet of lead wire or such heavy material wrapped around the pipe in a few locations. Put these dampeners on in a couple of locations, by moving them back and forth about 6" on either side you could find the "sweet spot" that stops resonance.



Hmmm, lead wire might melt on the hotter parts of the exhaust upstream, so copper wire might be a better solution. Cheap, fast, and simple.