I have had Pantera mufflers on my Mangusta / Corvette since 1972. Displacement is 350CI with 2.25" header pipe.  They came off of a car that was being worked on at Ford R & D in Dearborn.  

They were fine for about 35,000 miles and then I started to get the dreaded "drone" between 18 and 2,200 RPM where most of my driving is.  I have a new set of what is available from Hall Pantera.  I am worried about the return of the "drone" when I put them on.

Has anyone had that problem when putting a new set on a car?

DICK RUZZIN / 8MA670

Original Post

Hi Dick, my '72 has a massive resonance around 1800 rpm but it fades quicker than your situation....maybe by 2000 rpm it's mostly gone. In that small range, however, the rumble must be rattling all the neighbor's windows....I'm sure they appreciate that lots!   I don't remember where the mufflers were from but they are stock upswept (i.e., early type) Ansas.  The resonance was there from new, I always assumed it was normal with some of these systems.

In the archives are complaints dating back to the '70s of exhaust resonance or drone, and all sorts of fixes that cured or lessened the noise on certain cars. About all they agree on is, it originates from the exhaust. Surprisingly, this is also quite a subject on Corvette forums.

In my (Mustang) experience, straight-through mufflers (ie Mangaflow) are less prone to droning while chambered mufflers (ie Flowmaster and I believe the Ansa's as well) are more prone. Also, the further you can move the muffler from the passenger cabin the better off you are. Modern cars intentionally moved the mufflers to the rear of the car rather than underneath the passengers.

 

 

The sound is one thing and the drone is another.  

I am very disappointed in the mufflers from Hall as they are presented on their site as "The quiet European muffler" if I recall.  The drone is different but still there, in a slightly lower RPM range. I guess at this point that it is my engine / headers. Their supplier then told me that only "performance mufflers" for the Pantera have been imported into the USA for years.  I checked that with a tech in his company who has been there since 1980 and he said the same thing.  

I spoke to a great engineer at VIBRANT, a company that sells different exhaust parts and he suggests resonators and a flex joint to eliminate vibration and stress in the system.  I really do not have room for both on each header pipe.

There is also such a thing as an exhaust dampner, these are on a lot of cars but each is carefully configured by cam design, stroke, etc.  Very scientific so that is out.

I would appreciate any ideas from anyone with experience in this field.

MUFFLER DRAWING.P1030331 copy

DICK RUZZIN

 

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Dear Dick,

          Interestingly enough Gerry Romack and the Great Lakes Panteras have done some actual work on the drone resonance problem and find that it is from a Helmholtz Effect or Phenomenon (?).    I am attaching a link to their tech article.  I am intrigued by it and the handful of people that I have surveyed by email with experience doing it report that it *does* notably reduce the resonance.

           http://www.greatlakespantera.c...r%20Modification.pdf

 

                    Warmest regards,  Chuck Engles

 

 

Dear Modok,

       Alas, to my knowledge, there is no "final solution".  Lacking the resources of Flowmaster, we must rely on ourselves.  

       I emailed about three or four people that Gerry said had followed his method.   I got about two or three replies and they were positive.  The good news is that nobody reported things were worse.  

              Warmest regards,  Chuck Engles

This will not be of much help. Dick. Two obvious problems in designing (or redesigning) your own mufflers:

1)- We are trying to simultaneously remove waste gasses from 300-400+ bhp engines thru sound attenuators (mufflers) the size of kid's lunchboxes due to lack of space, control the  noise from combustion explosions very close by us, and also maximize horsepower from the engine. A dynomometer is a necessary tool for testing power gains or losses IMHO. Everything else is a pure guess.

2)- We need some way of quantifying any change in noise. No one including pro builders of mufflers ever mentions gains or losses in noise levels except subjectively. There are standards for exhaust noise testing with a dB meter but it will not separate 'drone' from other exhaust noises. Depends on your hearing acuity and personal noise tolerance. For instance, I can stand far more volume of Beethoven than what passes for 'music' these days.

Hot-rodders found eons ago that stuffing most any muffler with fiberglas strands or steel mesh works well but not for long. Heat (maybe 350F), vibration and exhaust pulsations soon tear them apart & blow the little fragments out the pipes. Back in the '50s we used brillo pads with the soap removed, or curly steel lathe shavings begged from machine shops . A few muffler mfgrs made take-apart mufflers back then so they could be easily 'reloaded'.

 

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