Exhaust Drone Question

[Notes]

72 C10. 350. New exhaust. Nice, straight exhaust pipes. Mufflers back as far as they can go. Tail pipes exit behind rear weels. Drone. Changed out mufflers to stock design. Much quieter, but at speeds above 60, it still drones. Question is - isn't a drone constant? This is now a rapid pulsation. It's almost worse than if it was constant. Thought it might be a wheel out of balance, but it goes away when I let it coast at speed. Any ideas?

[dagnabbitt]

Originally Posted by Notes

72 C10. 350. New exhaust. Nice, straight exhaust pipes. Mufflers back as far as they can go. Tail pipes exit behind rear weels. Drone. Changed out mufflers to stock design. Much quieter, but at speeds above 60, it still drones. Question is - isn't a drone constant? This is now a rapid pulsation. It's almost worse than if it was constant. Thought it might be a wheel out of balance, but it goes away when I let it coast at speed. Any ideas?

Do you have a pipe that is really close to the frame? Might be flexing under WOT and touching, that could cause it.

[truckster]

Are you running headers or stock manifolds?

[Notes]

WOT is not an issue. Stock manifolds.

[mkmc69]

Do you have an H or an X pipe? If not, I wonder if this would help. Just a thought.

[Steeveedee]

Yes an h- or x-pipe can settle out some of the noise. I prefer an h-pipe, but a lot of Buick guys swear by x-pipes. The connection reduces some of the pressure from the pulses as they are scavenged back and forth. The other reason is that it effectively doubles the frequency of the exhaust note, and the higher frequencies aren't as annoying as they have less energy.

[jayoldschool]

Ensure no rubbing. Add crossover. Add resonators out back.

[LockDoc]

-
"J" pipe cured my drone around 60mph.

Picture of a "J" pipe and length calculator.

Install as close to the back of the muffler as possible. End is capped off

Mine are 27" long.

LockDoc

[Steeveedee]

Worse comes to worst, put a pair of Cadillac mufflers on it. Those will give no rumble whatsoever. Ever heard a loud, stock Caddy? A couple to fit a 500 Cu In engine would be sure to give you enough flow! When I go to do mine, that's the route I'm taking.

[Notes]

Thanks for all the replies. Still curious, though. Is a drone constant? Mine pulsates. Wondering if it really is exhaust related, although don't know what else it would be.

[kwmech]

With the cast manifolds I'd personally go with a single 3'' pipe instead of the duals

[special-K]

Sounds are hard to describe. But I consider a drone to be a constant hum to a very rapid pulsation creating a hum. I define drone as a constant harmonic and pulsation as constant rapid sounds. I run headers, never ran a crossover, and I don't feel I have had a drone in any of my vehicles I've had. Just the sound made coming out the pipes. The only time I've had a drone is with exhaust not exiting out from under the body

[LockDoc]

Originally Posted by Notes

Thanks for all the replies. Still curious, though. Is a drone constant? Mine pulsates. Wondering if it really is exhaust related, although don't know what else it would be.

Type this into Google..... "what causes drone in a custom exhaust". or copy and paste it.

LockDoc

[LS short box]

No muffler expert by a long shot. I'm running headers, 3" collectors reduced down to 2.5", then non-xpiped to the bumper. Running Dyno Max super turbo mufflers. Zero drone.
But when I did the cab insulation I put down a layer of dynamat like insulation then the double foil sided jute insulation. Then the carpet. Did the insulation from the firewall to the back of the cab to where the gas tank would of been. Again zero drone.
One more thing. When I was much younger I worked for a Chev dealership and we were the first with a exhaust pipe bender and the training we had from the supplier was that the first exhaust hanger after the manifold was at the muffler. It gives some flex to the exhaust system.

[Already Gone]

I have DynoMax SuperTurbos on mine and an H pipe and no drone. I'd post a video of it idling if I could on here.

[davischevy]

My dad bought a new 69 that had the drone and I had a 72 Cheyenne Super that had it. I changed exhaust and hangers, motor mounts, transmission mount, and tried any thing else I could think of. I never did find it.

[HO455]

Originally Posted by Notes

72 C10. 350. New exhaust. Nice, straight exhaust pipes. Mufflers back as far as they can go. Tail pipes exit behind rear weels. Drone. Changed out mufflers to stock design. Much quieter, but at speeds above 60, it still drones. Question is - isn't a drone constant? This is now a rapid pulsation. It's almost worse than if it was constant. Thought it might be a wheel out of balance, but it goes away when I let it coast at speed. Any ideas?

No drone of any kind before the new exhaust system?
I will say that straight pipes are noisy in their own way which is why you never see them installed from the factory. Straight pipes would be cheaper to build, but manufacturers are willing to spend money for bent pipes. Obviously packaging is a concern in all newer vehicles but when was the last time you saw factory straight pipe?
I have found that tires are usually the culprit when a pulsing noise is heard. Can you swap them? It would be good to confirm one way or the other before spending money on exhaust items.

[6T7 C10]

I have what Lock Doc describes on my daily driver without a muffler and it works perfectly. Drone is not a constant and that Helmholtz tube has to be tuned to length work for the frequency the drone occurs worst at.

Another trick is to put in a short glass pack muffler as a resonator. With that and the X/Y pipes is you are breaking up the long runs of uninterupted pipe.

[Sheepdip]

X or H pipe will cure 80% if not all of it

[tdangle]

I have a 2 1/2" dual system stock ram manifolds, H pipe, dynomax mufflers and exits rear under bumper. No drone and sounds great a low speeds especially with the windows down. At highway speeds with windows up and A/C running I hear more tire and wind noise than exhaust.

[Notes]

Great replies. I appreciate all of them. If I can borrow a couple from a friend, I'll try swapping tires first and see if that works. Then go from there. Lots of variables to consider.

[Notes]

Update: I was feeling kind of down about the drone with the new exhaust. Had a beer in the garage & noticed 2 rubber floor mats my wife brought out from the kitchen. She didn't want them anymore. They're fairly heavy, quilted, and have about 1/2" of foam in them. I moved the seat forward, pushed them in vertically against the gas tank & then moved the seat back. No more drone at highway speeds anymore! If it's windy, I still get that pulsing a bit, but no where near as bad as it was. Beer to the rescue yet again.

[Ironangel]

Drone is a constant that can come at varying harmonics...The sheet metal harmonics and the exhaust tones can interact to cause "drone" at varying speeds. The tires can come into play as well if they happen to emit a tone that harmonizes with the sheet metal and/or exhaust tone. LockDoc gave the fix, install a J pipe on each exhaust pipe located across from eachother. If that don't work install a crossover pipe between the J pipes and you'll have a tone and pressure equalizer that may render the whole system dead quiet...Interrupt the constant and you'll kill the drone...Might check the rear end lube while your down there because them worn gears can emit a drone as well...

[Steeveedee]

Originally Posted by Ironangel

Drone is a constant that can come at varying harmonics...The sheet metal harmonics and the exhaust tones can interact to cause "drone" at varying speeds. The tires can come into play as well if they happen to emit a tone that harmonizes with the sheet metal and/or exhaust tone. LockDoc gave the fix, install a J pipe on each exhaust pipe located across from eachother. If that don't work install a crossover pipe between the J pipes and you'll have a tone and pressure equalizer that may render the whole system dead quiet...Interrupt the constant and you'll kill the drone...Might check the rear end lube while your down there because them worn gears can emit a drone as well...

Indeed, it could well be rear gear noise, and I have heard ones that had a varying level of sound.

[bigmoe]

Originally Posted by LockDoc

-
"J" pipe cured my drone around 60mph.

Picture of a "J" pipe and length calculator.

Install as close to the back of the muffler as possible. End is capped off

Mine are 27" long.

LockDoc

LockDoc when you measure the length where exactly are you measuring? You could measure total length of pipe before bending or just top to bottom of the J.
I've got a lot of drone with my shorties and Magnaflow 3 chambers. Truck is going in this week for tailpipes (now just turn downs) and I hope that will reduce or eliminate my drone which is deafening at 18-2000. I keep it in a lower gear and higher revs when I can to avoid it.

EDIT: Got my tail pipes installed and it cured the drone. Much nicer to drive around. Rumbles at low throttle but still loud when tromped on.