C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

The Official Exhaust Resonance Post!

 
Old 08-22-2007, 11:57 AM
  #21  
bogus
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there is one more factor... the design - ie acoustics - of the cabin. it's a resonance chamber!

do a little insulating should help.
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Old 08-22-2007, 08:09 PM
  #22  
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Doing GOOGLE, it looks like 121-C / 250F,, so exhaust at 250F, I doubt very very highly that the exhaust reaches this temp at the exit of the muffler.
No worries
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Old 08-22-2007, 09:02 PM
  #23  
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A bag of Steel Wool cost be $1.99 at Home Depot, I take 4-pieces and unroll two of them and wrap them around the other two pieces, the push it into one side of the exhaust.

So this is the end result, resonance gone,, lost maybe 2-5 hp,,,

for me no issues,

Reversible, pull it out when you go to the track but on the street, you wont miss 2-5 hp.
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Old 08-22-2007, 11:11 PM
  #24  
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What is this "resonance" of which you speak?

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Old 08-23-2007, 12:02 AM
  #25  
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hey mike we didn't say show us your bootie

Last edited by coupeguy2001; 08-23-2007 at 12:06 AM.
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Old 09-07-2007, 01:07 AM
  #26  
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Have input on this for the books?
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Old 09-07-2007, 01:43 AM
  #27  
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its a short exhaust system to begin with and mufflers being the exit with no tailpipe afterwards makes the chances of resonance real high if something is changed.
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Old 09-07-2007, 01:44 AM
  #28  
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Originally Posted by bogus View Post
there is one more factor... the design - ie acoustics - of the cabin. it's a resonance chamber!

do a little insulating should help.
True. If you insulate the rear cabin, it will reduce it. When I put my roll bar in, S/T Frame, the holes cut into the interior werent insulated till I got home. I thought I had open headers. I have heard you can get rid of allot of the noise through insulation. It wont cost much, actually, as there isnt much back there, in our hatch area.
Of course gears help, as you will not be in that rpm range often
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Old 09-07-2007, 07:28 AM
  #29  
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I have two Magnaflows with stock resonator and stock cats with the tipe extended past the bumper. I do have resonance at 1000-1500 rpm's.

Last edited by runner140*; 09-07-2007 at 07:31 AM. Reason: correction
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Old 09-07-2007, 07:50 AM
  #30  
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Hey lt4obsesses,
I had a local shop remove my mufflers and the sound is great but the resonance is terrible in city traffic. You wouldn't have the part number of the magnaflow muffler you used would you? I think that is what I need!
Bernie
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Old 09-07-2007, 08:29 AM
  #31  
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Why couldnt Chevrolet just have come up with something like they did in 1962 called Off road exhaust system, and just give C4 and C5 owners a specific sound which would stop all this tension of trying to get their exhaust system right.The closest I ever heard a car have that specific old Corvette sound was my sons 85 Z28 with headers and one flowmaster muffler which sat in front of the rear axle, And there was NO resonance at all. My 84 has flowmaster 40s with gutted cat and does not sound as good as his car and the resonance is very loud.His did have a 305 if that makes any difference?
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Old 09-07-2007, 10:54 AM
  #32  
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Originally Posted by bogus View Post
there is one more factor... the design - ie acoustics - of the cabin. it's a resonance chamber!

do a little insulating should help.
Does anyone know if switching to the mass backed carpet replacements from wilcox helps with the insulation? Or do you really need a layer of acoustic insulation in there too? I really think dampening the sound in the interior is a large part of the key to reducing resonance. The interior on my '85 transfers so much sound on the highway and I know a lot of it is road noise too, not just exhaust.
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Old 09-07-2007, 11:03 AM
  #33  
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Mass backing will definitely help as opposed to not having it.

Magnaflows will still resonate btw.
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Old 09-07-2007, 01:48 PM
  #34  
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My solution... (not eliminated, but GREATLY reduced)
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Old 09-09-2007, 03:24 PM
  #35  
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Resonance between 1100-2000 is bad. Even in this clip when Im just crusing the rpm range is well above that and still booms...

This is with dual 3's, dual dynomax "bullet" resonators and Dynomax super turbos. Bet with a smaller pipe it would be more manageable.

[/url]
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Old 09-09-2007, 04:07 PM
  #36  
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About the steel wool trick... doesn't steel wool rust like crazy when you have it in a hot, occasionally moist place like the mufflers? Wouldn't that rust spread to the mufflers? Or is there some sort of "stainless steel wool" you can buy?
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Old 09-09-2007, 06:49 PM
  #37  
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Default steel wool installed

I tried the steel wool trick years ago. On my car, I had a set of smittys and scavenger pipes, and got a noise ticket. So I poked steel wool up the pipes, (drilled holes in the pipes to hold the wool in them) and drove to the other town to get signed off. It worked, and Man it was quiet!! It was neat dark when I left and so I pushed it up to the neat triple mark. I passed this car, and got about 50 feet ahead of him, and two great big ***** of burning steel wool rolled out and scared the living crap out of us. Yes steel wool will get hot and glow from really hot exhaust. That my lesson
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Old 09-09-2007, 09:02 PM
  #38  
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Originally Posted by ps374 View Post
Why couldnt Chevrolet just have come up with something like they did in 1962 called Off road exhaust system, and just give C4 and C5 owners a specific sound which would stop all this tension of trying to get their exhaust system right.The closest I ever heard a car have that specific old Corvette sound was my sons 85 Z28 with headers and one flowmaster muffler which sat in front of the rear axle, And there was NO resonance at all. My 84 has flowmaster 40s with gutted cat and does not sound as good as his car and the resonance is very loud.His did have a 305 if that makes any difference?
PS374 may be on to something. Has anyone tried to come straight off the cat with a single flowmaster or Magnaflow with the built in x pipe
and dual outputs to run to the back. It would be similar to a eliminator setup with one muffler. Would that be too restrictive?
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Old 09-09-2007, 09:18 PM
  #39  
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Originally Posted by LouisvilleLT4 View Post
About the steel wool trick... doesn't steel wool rust like crazy when you have it in a hot, occasionally moist place like the mufflers? Wouldn't that rust spread to the mufflers? Or is there some sort of "stainless steel wool" you can buy?
Mine is always coated with black carbon, so, no, I have not seen any rust on the steel wool


crossfire84 = "two great big ***** of burning steel wool rolled out and scared the living crap out of us. Yes steel wool will get hot and glow from really hot exhaust. That my lesson" No way your exhaust got up to 250f
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Old 10-14-2007, 12:56 PM
  #40  
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Default X pipe

Would like to hear a bit more on x-pipe experiences! The effects on sound and resonance!?
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