Experts Please Explain?!!?
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
Experts Please Explain?!!?
When I got my '66 coupe ten years ago, the previous owner had put in a 383 stroker motor. I don't know the internal specs, but it makes lots of torque. But, it's always had a vibration. It's a rythmic vibration that starts to be noticeable about 1800-2000 rpm. At that speed its like 3/4 second vibrate, 3/4 second smooth, 3/4 second vibrate, 3/4 second smooth. The frequency goes up with engine speed. At around 3500 rpm it's more like 1/4 second vibrate, 14 second smooth, etc. It's a strong vibration -- it can be felt in the floor, the seat, the shifter. The flywheel is the correct one for external balance, checked that out years ago when I changed the clutch, etc. I put on a Fluidamper balancer, and that didn't make any difference.
So I just put on a new exhaust system. It has the same headers as before, and the same pipes from the header collectors to the trans mount bracket. From there back, it's a new 2-1/2" chambered pipe system. Went for a long drive on Saturday, and the vibration is gone! How does that work? The old system was the standard pipes with some no-name mufflers hanging in the back.
The car is much more pleasant to drive, but how does changing the exhaust take care of a vibration like that?
So I just put on a new exhaust system. It has the same headers as before, and the same pipes from the header collectors to the trans mount bracket. From there back, it's a new 2-1/2" chambered pipe system. Went for a long drive on Saturday, and the vibration is gone! How does that work? The old system was the standard pipes with some no-name mufflers hanging in the back.
The car is much more pleasant to drive, but how does changing the exhaust take care of a vibration like that?
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
When I got my '66 coupe ten years ago, the previous owner had put in a 383 stroker motor. I don't know the internal specs, but it makes lots of torque. But, it's always had a vibration. It's a rythmic vibration that starts to be noticeable about 1800-2000 rpm. At that speed its like 3/4 second vibrate, 3/4 second smooth, 3/4 second vibrate, 3/4 second smooth. The frequency goes up with engine speed. At around 3500 rpm it's more like 1/4 second vibrate, 14 second smooth, etc. It's a strong vibration -- it can be felt in the floor, the seat, the shifter. The flywheel is the correct one for external balance, checked that out years ago when I changed the clutch, etc. I put on a Fluidamper balancer, and that didn't make any difference.
So I just put on a new exhaust system. It has the same headers as before, and the same pipes from the header collectors to the trans mount bracket. From there back, it's a new 2-1/2" chambered pipe system. Went for a long drive on Saturday, and the vibration is gone! How does that work? The old system was the standard pipes with some no-name mufflers hanging in the back.
The car is much more pleasant to drive, but how does changing the exhaust take care of a vibration like that?
So I just put on a new exhaust system. It has the same headers as before, and the same pipes from the header collectors to the trans mount bracket. From there back, it's a new 2-1/2" chambered pipe system. Went for a long drive on Saturday, and the vibration is gone! How does that work? The old system was the standard pipes with some no-name mufflers hanging in the back.
The car is much more pleasant to drive, but how does changing the exhaust take care of a vibration like that?
Harmonics man Harmonics
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Sounds like the old exhaust was vibrating on the frame and the new exhaust isn't.
Drifting
Joined: Oct 1999
Posts: 1,276
Likes: 25
From: whitney pt. N.Y., USA ny
I have an original 63 convertible with OFF Road exhaust A GREAT sound from my 327/340hp solid lifter motor. So When I needed a new exhaust for a 67 327/350 convertible I decided to use a new chambered under body exhaust. IT WAS HORRIBLE!!!! I checked 6 ways from Sunday it was NOT touching anywhere. But the resonance was unbearable. I took it off after only a few hundred miles. I have heard about newer Vettes with certain after market exhausts being very unfriendly. I only know what I had was Bad.
Race Director
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From: Beverly Hills (Pine Ridge) Florida
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Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
Would a harmonic be all the way across the rpm range? It happened everywhere, it just change frequency.
My only problem with the undercar chambered exhaust is that it's too quiet. I think the old system was louder. Maybe the chambered system is just as loud, but is a different tone. I'll get used to it. So far, I'm liking the sound of the Flowmaster 50s I put on my Camaro better.
My only problem with the undercar chambered exhaust is that it's too quiet. I think the old system was louder. Maybe the chambered system is just as loud, but is a different tone. I'll get used to it. So far, I'm liking the sound of the Flowmaster 50s I put on my Camaro better.
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Would a harmonic be all the way across the rpm range? It happened everywhere, it just change frequency.
My only problem with the undercar chambered exhaust is that it's too quiet. I think the old system was louder. Maybe the chambered system is just as loud, but is a different tone. I'll get used to it. So far, I'm liking the sound of the Flowmaster 50s I put on my Camaro better.
My only problem with the undercar chambered exhaust is that it's too quiet. I think the old system was louder. Maybe the chambered system is just as loud, but is a different tone. I'll get used to it. So far, I'm liking the sound of the Flowmaster 50s I put on my Camaro better.
Harmonics are funny things sometimes. Many times when my customers complain of vibrations, I just take the torch to the pipes and heat a section red. Reduction of the stresses totally stoped the vibrations.
Pro
Joined: Jan 2007
Posts: 524
Likes: 12
From: Auckland New Zealand
Don't know if you saw an episode of Mythbusters where they used a small actuator with a weight on each end (only a kilogram or two).
They clamped it onto a large structure - a disused steel 4 lane road bridge !!! - then got the actuator oscillating and tweaked it until they found the resonant frequency of the bridge. They could actually see and feel the vibration set up by this relatively tiny actuator on this massive structure.
I have read that the military have played around with sound waves and resonance as a weapon - turns living things to jelly in seconds.
Last edited by Nev Williams; Oct 16, 2007 at 01:20 AM.
Team Owner
Joined: Oct 2004
Posts: 23,831
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From: Springfield MO
St. Jude Donor '07
Harmonics can be powerful stuff once resonance is established.
Don't know if you saw an episode of Mythbusters where they used a small actuator with a weight on each end (only a kilogram or two).
They clamped it onto a large structure - a disused steel 4 lane road bridge !!! - then got the actuator oscillating and tweaked it until they found the resonant frequency of the bridge. They could actually see and feel the vibration set up by this relatively tiny actuator on this massive structure.
I have read that the military have played around with sound waves and resonance as a weapon - turns living things to jelly in seconds.
Don't know if you saw an episode of Mythbusters where they used a small actuator with a weight on each end (only a kilogram or two).
They clamped it onto a large structure - a disused steel 4 lane road bridge !!! - then got the actuator oscillating and tweaked it until they found the resonant frequency of the bridge. They could actually see and feel the vibration set up by this relatively tiny actuator on this massive structure.
I have read that the military have played around with sound waves and resonance as a weapon - turns living things to jelly in seconds.
Drifting
Joined: Dec 2005
Posts: 1,973
Likes: 5
From: Valrico Florida
This was another Myth Buster episode. I won't spoil the conclusion for you.
Instructor
Joined: Jun 2006
Posts: 140
Likes: 0
From: Bergen, Norway
Today I made a 2"-crossower on my -66 327"with sidepipes, since I have the smaller oil-pan I was able to run the crossover-tube straight across from each downpipe, it looks neat and the exhaust note did change to a softer tone but even if the exhaust assy. is not touching the frame I did notice a slight vibration in the floorpan during cruise which I didn't have before. Maybe this is some kind of resonance problem?
Team Owner
Joined: Oct 2004
Posts: 23,831
Likes: 10
From: Springfield MO
St. Jude Donor '07
Even in the re-test, they missed the point. It's not the weight that causes the collapse, it's the harmonic vibrations.
At least two bridges have collapsed in modern times because of marching soldiers - in Manchester, England in 1831 and Angers, France in 1850. It's the same sort of harmonic oscillation that caused the Tacoma Narrows bridge to fly apart in 1940, and I'm pretty sure we've all see that video. The Millennium Bridge in London had problems with pedestrians unintentionally walking in step (matching their gait to the bridge's vibrations) causing harmonic vibrations in 2000, which led to the installation of dampers to change the harmonic frequency of the structure to eliminate the vibrations.
http://en.wikipedia.org/wiki/Angers_Bridge
http://en.wikipedia.org/wiki/Millenn...e_%28London%29
http://www.iit.edu/~smart/acadyear/resonance.htm
Instructor
Joined: Oct 2006
Posts: 224
Likes: 0
From: Lawrence Massachusetts
I have an original 63 convertible with OFF Road exhaust A GREAT sound from my 327/340hp solid lifter motor. So When I needed a new exhaust for a 67 327/350 convertible I decided to use a new chambered under body exhaust. IT WAS HORRIBLE!!!! I checked 6 ways from Sunday it was NOT touching anywhere. But the resonance was unbearable. I took it off after only a few hundred miles. I have heard about newer Vettes with certain after market exhausts being very unfriendly. I only know what I had was Bad.