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

The Official Exhaust Resonance Post!

Old 02-09-2008, 02:44 PM
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I have stock manifolds, stock cats, removed the middle resonator and replaced with straight pipes, then Flowmasters on the end; and they sound fabulous outside but have always resonated badly inside. I double insulated the interior with a foam and foil type sound insulator which helped some but not a lot.

It just so happens that I live in a desert environment and I have a smoked glass top which allows the sun to bake my brains even on short trips, so I decided to make an insulated headliner to block the sun. I made it out of foamed headliner from a Buick and covered it with black fabric-really looks nice. Then, after I fit it in the top, I discovered not only does it protect my head from the sun, but it also absorbs some of the resonation noise. It turns out the large glass panel overhead reflects a lot of resonation noise, and your head is right up next to it. This mod has been the single most effective change to date for reducing the noise.

I also think additional hangers supporting the muffler system would help. I'm going to try that once it warms up around here.

On the muffler/x-pipe combo thing, x-pipes do two things--they balance the flow between two pipes, and they help suck gas from one side as gas from the other side shoots past the X, like headers do. My thoughts are, if you do the perforated x muffler thing, you loose the scavenge effect because the x is perforated up-line from the x. Gases shooting past the x will just suck the gasses inside the muffler instead of sucking on the upline pipe. It will still help balance out the pulses though. Just something to think about.
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Old 02-09-2008, 03:39 PM
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While dealing with the symptoms of resonance may make the interior
less unpleasant, dealing with the cause of resonance is more desireable.

Some research and math might lead to information that would help
in the design and construction of Helmholtz chambers for the purpose
of attenuating resonance &/or moving the RPM at which it occurs.

Something as simple as adding closed-ended lengths of tubing branching
off from the main system could result in reducing resonance to more
acceptable levels.

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Old 02-09-2008, 04:06 PM
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I have elims that go just past the rear bumper.

I find none when I have the top off. When the top is on there is a little ...

My muffler elims
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Old 05-15-2012, 01:52 PM
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Default timster9

Originally Posted by jakers View Post
I would like to consolidate the info on how the C4 nation has reduced or eliminated resonance. Yeah I know, go spend a $1200 on a Corsa, well for some of us that may not be a viable option in the immediate future! So anything else work. Say like cats or cones in the header etc... etc... ?

If you have successfully limited or eliminated resonance please share your technology...
I read about blocking, or plugging the inside pipes on each muffler. I just tried it and took it for a ride. "The resonance is nearly gone completely" and I am thrilled. I have no cats (cats needed to be replaced and I didn't want to spend the money), and the last set I bought was from Ecklers with "no drone". I am no mechanic but thought for a long time that the drone was probably still there because I had the cats removed.

Anyway, I wrapped reynolds wrap around a hanger (so I could pull them if it didn't work). You may want to try it.

I would love to get some noise out the rear without the drone and want to try some louder ones and block one side again. If someone has any comments or "don't' agree let me know.
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