Reduce exhaust drone

I have a 70 Cuda with 440, 2.5 inch exhaust with H pipe and flow master mufflers. Car sounds great, but the drone kills me on long drives. Has anyone added a rear resonator to reduce the drone. Something I can tuck up beside the fuel tank like the original car layout had but in 2.5 inch. Appreciate it.

Try the Hemi resonators? Another muffler is the Magnafow. Nice rumble at idle and fairly quiet while cruising. No drone. I think TTI uses them in their exhaust sets.

IMO every car is a little different. A combo that drones on one car may not drone on another car. And what fixes drone on one car may not fix it on another.

That said....my 70 RR with a 440 and flowmasters droned like crazy. I made a switch from an "H" crossover to an X pipe and the drone disappeared--no other changes.

Some guys I hang out with also used glasspacks as resonators near the tailpipe for this purpose with mixed results.

I basically have your same car with the same exhaust. On this one and all my other Mopars, I have killed the drone by putting glass packs (bullets) beside the gas tank in the tail pipes. Any cheap ones will work, no need to spend any big bucks.

Thanks all. That was where I was thinking of starting (Glass pack, etc near the tailpipe to see how that works first).

Adding the glasspacks works for some folks; I'll assume you have tailpipes.
Like wingman says, every car seems to be different:
I've had Flowmasters on 2.5" to the rear bumper w/tips on a 406" SB Duster, no drone.
Everything (3 different mufflers) I put on a '64 wagon droned until I added tailpipes to the rear corners.
3" w/Flowmasters in another Duster (512") would drive you out of the car pretty much anytime, until I added tailpipes.
Also, the different models of Flowmasters have different characteristics.
They're not my go-to mufflers, but came on the Dusters I'm referring to.

this ^^^^^^
however, you might have to experiment with the length of the glass packs [or race bullets] to get the results you need or want.
it is best to put the glass packs just past where the pipe comes over the housing and starts rearward by the gas tank, so you have room for the tip or turn down of your choice.
another way would be to get your tip/turn down in the position you want, then measure what length of glass pack will work, attaching to your tip and the tail pipe coming rearward.

Some choices here https://www.wesdonautomotive.com/welded-resonators/?sort=featured&page=1

Classic Chambered Exhaust made me a set for my 70 Challenger. They mount beside the gas tank and he is a member here. I took a few dimensions and emailed him and he told me what he could make. They fit perfect beside the tank and fit well with the aftermarket exhaust tips.

Fwiw, I would just change the mufflers. I like pypes race pro. They are straight through but one of the quieter mufflers out there. (more so than magnaflow or dynomax ultra flo) I have zero drone with h-pipe and dual 3".

Friend of mine has a roadrunner with dual 2.5" and x-pipe with the same mufflers and sounds great as well.

I am & thank you.

👍

being too rich increased drone

I have full 3 " with Flowmaster super 40's and have no drone.

Helmholtz Resonance-
the concept of this resonator is quite complicated when trying to understand how sound and frequency works, but the steps involved are fairly simple. here's how:

1. you will need two variables: the drone RPM, and # of cylinders your engine has.
2. divide the RPM by 60 to get the RPS, or revolutions per second.
3. divide the # of cylinders by 2 to get # fired per revolution.
4. multiply RPS by # fired per rev to get the drone frequency in Hz.
5. divide the speed of sound by the Hz. the speed of sound is a constant 1,260 ft/s. the number is funky because sound travels faster in warm air, and the air coming from an exhaust is very hot.
6. take the result from #5 and divide by 4.
7. take the result from #6 and multiply by 12 to get the resonator length in inches needed to cancel the drone at that RPM.

here's an example:

1. my car drones the worst at 3,300 RPM and has 4 cylinders.
2. 3,300 / 60 = 55.0 RPS
3. 4 / 2 = 2
4. 55.0 * 2 = 110 Hz
5. 1,260 / 110 = 11.45
6. 11.45 / 4 = 2.86
7. 2.86 * 12 = 34.36 inches

from the result shown, my car needs a resonator of approximately 34.4 inches to add a damper that is tuned for my drone.

Hope this helps.

These Flowmaster resonators fixed the drone on my 6.1 Hemi Cuda with 2.5" TTI headers & exhaust. https://www.holley.com/products/exhaust/builder_components/resonator/parts/15150S

That's a first!

WAAAAAAY too technical!

Interesting.

In step #5 above
a questionable assumption is made
to ignore how the speed of sound in a gas varies with
temperature,
pressure,
and what the gas is a mixture of ( various percents of nitrogen, carbon dioxide, water vapor, oxygen)

Maybe 1,260 feet per second is “close enough.”

In past Moparts posts on “Drone” we have discussed “stubs” for reduction
instead of resonators.

Another post above points out that whether the air/fuel mixture is rich or lean affects Drone.
This is also saying: rich or lean affects the speed of sound of exhaust gas.

Drone will change if you climb a steep hill at constant speed. (pressure of exhaust gas goes up)

Drone will change if you vice grip a large socket into your exhaust pipe tip. (pressure again)

Do you have any videos with the Pypes Race Pro?

https://www.youtube.com/watch?v=ADM5jqrUcTI


https://www.youtube.com/watch?v=422uTiz78bs