I have Flowmaster 40 series mufflers on my 93 Vette LT1 and I complaned to the muffler shop that installed them about the interior noise I'm getting at about 1800 rpm in high gear. What I'm trying out is putting counterweights in front of the mufflers. The theory
is that the noise or vibration starts at the engine and amplifies as it moves to the rear. By stragically placing these counterweights, they will absorb the noise or vibration being produced. It seems to help so far, but I need to get out on a 65mph highway to really test it. I should have the results by early next week. What do you think of this theory?
The way this is done is to weld a weight to a exhaust clamp, and place it in front of your muffler, one on each side. Try it, you might like it.
Please let me know of your findings.

 

hmmmmm strange theory..never heard of this being done....but let us know Jim.....a lot of us here are plagued with resonance and FLOWMASTER from what I have heard is one of the bigger complaints.....a weight on the muffler clamp....hmmmmm

let us know

 

Hmmmmmm! Be real interested to hear the results.

 

I've never heard of that fix before. I have Flowmasters with dumps on my car till I get the tail-pipes done. At certain RPM's I can watch my rearview mirror shake like a loud stereo. If it workks I'll try it, let us know. I'll probably put the tail-pipes on first and see what it sounds like. :flag

 

Jim,

I'm not sure this would hold true for an LT-1, but on my L98 the resonance disappeared when I put in 3.73 gears. I could also mostly get rid of it if I drove in D rather than OD before the gears. It seems that if you keep the revs up the noise disappears. :yesnod:

 

You may be on to something.

There are examples of similar fixes in the auto industry. On my 1969 Camaro with monoleaf rear springs, the factory clamped a 2 lb weight to the spring about half way between the axle and front spring mount. These were to reduce vibration harmonics induced at certain road speeds. They also help to damped wheel hop common to monoleaf springs.

The drone is induced by a narrow band of vibrations (sound wave length) created by the muffler at a specific RPM that is greatly amplified within the Corvette's complementary diminsion rear compartment. Home stereo speaker manufactures and auditorium designers have know for decades that a speaker cabinet or the room dimension has a tremendous affect on the frequency response in a room.

You can reduce (but not eliminate) the drone by laying heavy blankets in the rear compartment. This does two things: 1) reduce the soundwaves that travel into the rear compartment and 2) dampen the reflections from the rear glass. What the weights do is dampen specific frequencies generated by the muffler at a specific RPM. Its like stricking drinking glasses with different amounts of water.

Things you may try are difference sizes and location of the weights or even multiple weights. By modifying a muffler's basic vibration characteristics with mass placed at various points seems to me a reasonable avenue of experimentation. You may want to glue a 5 lb. lead weight to the bottom of the rear storage compartment to see what that does.

Go for it.



[Modified by Mez, 3:54 PM 10/25/2002]

 

MODS, MODS, MODS.........will we never learn? Jim, with your vette sitting quietly for a week, one would surmise that you would be delighted to hear any noise coming from the exhaust system. :nopity