Exhaust drone - dumped at axle

R/T_Fire · Feb 11, 2017

So tomorrow im cutting my exhaust before the axle and installing turn downs to be able to adjust my rear diff correctly and solve a conflict.
My thought and fear is introducing a drone effect, and am wondering if directiin of the turn down sweep helps solve any of this or if it is an issue at all ?

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Markcuda · Feb 11, 2017

installing turn downs to be able to adjust my rear diff correctly

Please explain?
Your signature says your goal is low 12s, with out nitrous, it will cost a ton to achieve that, are you ready to spend BIG money?)))))))))

electricyeti · Feb 11, 2017

I would think turning out at about a 30 deg angle will reflect the sound away enough to eliminate most of it. I plan on doing about that angle with my exhaust cutout (when it arrives)

SilverStreak88 · Feb 11, 2017

In my years running dumped systems I've found that with a 90° you will have the most. A 45° will still give you drone, but not as bad, I've only run them on lifted trucks so I don't know what it's like with lowered trucks. It also depends on which muffler you run, I just welded up a 50 series this morning and it's got some sound (not to crazy), but enough for me. I don't like the way dumped exhaust systems sound when you jump it cause it just sounds like it's screaming, run out the back I get full sound and sounds cleaner.

sbarron · Feb 11, 2017

I'm at about a 45 down and out just behind the axle and still have drone sometimes.

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07MegaCabRam · Feb 11, 2017

Drone is sound frequency and you will not alter it with a angle of the exhaust exiting the muffler. The frequency is not effected by it.

R/T_Fire · Feb 11, 2017

07MegaCabRam said:
Drone is sound frequency and you will not alter it with a angle of the exhaust exiting the muffler. The frequency is not effected by it.

The the sound reflectance under the vehicle to ground is which the drone im talking about. Changing how the pipe flows and how it interacts by dumping it into a echo chamber under tge vehicle will increase or amplify that frequencys sound level with a dumped system. In turn making it louder and more noticeable and annoying
This is only temporary till I install the exhaust components sitting in the tool shed.

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sbarron · Feb 11, 2017

07MegaCabRam said:
Drone is sound frequency and you will not alter it with a angle of the exhaust exiting the muffler. The frequency is not effected by it.

Incorrect. EVERY twist, turn, restriction, pipe length or opening shape will effect drone/exhaust note and volume, some more than others. Hell, even tips effect it.

R/T_Fire · Feb 11, 2017

Markcuda said:
Please explain?
Your signature says your goal is low 12s, with out nitrous, it will cost a ton to achieve that, are you ready to spend BIG money?)))))))))

The exhaust system the previous owner had put on makes contact at the u-joint when the axles pinion angle is properly adjusted. My axle also makes contact with the axle hoop due to the modifications to the lowering kit.
And im well aware of the cost it takes to build a vehicle and reach a goal. This is not my first rodeo, nor 12, 11 or 10 second, hell even sub 4 second car i have built.

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R/T_Fire · Feb 11, 2017

sbarron said:
I'm at about a 45 down and out just behind the axle and still have drone sometimes.

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Do you have it swept to the side at 45 or a 45 miter straight out the back.
I was thinking what you and silverstreak said and going with a 30-45 out to the sides

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sbarron · Feb 11, 2017

R/T_Fire said:
Do you have it swept to the side at 45 or a 45 miter straight out the back.
I was thinking what you and silverstreak said and going with a 30-45 out to the sides

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Not the best picture, but you can see it's about 45 back and maybe 30 down.\

Edit: Forgot the picture. OOPS!

Edit 2: Other side is the same.

Cat-back duals. Drone isn't bad until MDS kicks in, then it's bad.

PCT · Feb 11, 2017

I ran a streetflow 75 dual turn on my 97 5.2, it was droney as f, but I was in highschool and liked it

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R/T_Fire · Feb 11, 2017

Ive got a super 10, so that has me a little worried. I dont really have any drone right now. But this will only be till summer i hope, since things never go as planned.
But my first car was a 67 mustang with ****** super comp headers and 18" purple ***** glass packs bolted right to the collector... thats prob why i have hearing problems these days

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blackbeautyhemi · Feb 11, 2017

Muffler location helps as well.

Csanders1992 · Feb 11, 2017

I had a lowered Colorado several years ago. I put a flowmaster 44 on it and dumped it right at the muffler. Drone was insane. I then ran more pipe and had it dumped after the axle with a 4" tip and it sounded awesome and didn't drone at all. It was still tucked up out of the way and didn't interfere with anything

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TylerB · Feb 12, 2017

My drone isn't too bad when moving, but sitting still it's pretty annoying when it's just reverberating under the bed.

My setup is a 45° right out of the muffler just before the axle clocked at about a 45° towards the passenger rear tire. I'll be changing it soon to dump it at the bed corner so it's not reverberating under there.

07MegaCabRam · Feb 12, 2017

sbarron said:
Incorrect. EVERY twist, turn, restriction, pipe length or opening shape will effect drone/exhaust note and volume, some more than others. Hell, even tips effect it.

f = RPM * pulses/rev * (1/60)

f = 2000 rev/min * 4 pulses/rev * (1/60)

f = 133.34 pulses/second = 133.34Hz

At 2000rpms, your V8 fires 4 times per revolution. RPM is in minutes, so divide by 60 to reduce to seconds. Now you need to find the length of the wave at the frequency you just calculated. Wavelength is denoted by lambda (λ), units are meters.

λ = v/f = speed of sound / frequency

λ = (343m/s)/(133.34Hz)

λ = 2.572 meters

:favorites13:

sbarron · Feb 12, 2017

And at 2001, 2002 rpm... ad Infinitum, you'll get a different number each time. Your exhaust hardware doesn't change. Everything is a compromise. Easy enough to eliminate the resonance at a certain RPM, however, that will only work at that particular RPM mathematically.

Remember that every twist turn, restriction, etc changes the flow of the exhaust gasses and redirects the sound waves sometimes speeding them, sometimes slowing them, sometimes even cancelling themselves out. In fact, it's mostly how mufflers work, by bouncing the sound waves back into themselves essentially self noise cancelling.

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R/T_Fire · Feb 13, 2017

Well it doesnt sound too bad, but didnt get a chance to finish, with the oriville damn issue and potential failure with portions of it my day got cut short and time to go deal with evacuations while the GF packs up the house and takes her and baby to higher ground...
If the damn fails i will probably be getting a new truck since it is sitting at the fire station in harms way. So in some ways the problems may solve themselves...

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R/T_Fire · Feb 13, 2017

sbarron said:
And at 2001, 2002 rpm... ad Infinitum, you'll get a different number each time. Your exhaust hardware doesn't change. Everything is a compromise. Easy enough to eliminate the resonance at a certain RPM, however, that will only work at that particular RPM mathematically.

Remember that every twist turn, restriction, etc changes the flow of the exhaust gasses and redirects the sound waves sometimes speeding them, sometimes slowing them, sometimes even cancelling themselves out. In fact, it's mostly how mufflers work, by bouncing the sound waves back into themselves essentially self noise cancelling.

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Simpler way to explaining it is to explaining how a organ works or a wine glass with the amount of water in it changes the tone, even changing the water level by a few drops or shape etc etc, it all changes the resonant frequency

Exhaust drone - dumped at axle

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