Resonance, where does it come from?
Safety Car
Joined: Jan 2004
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Again, the fix has been to block one of the outlets.
Quote from CC's website: Corvette Central is pleased to introduce our exclusive correct sounding dual outlet mufflers for the 1984-1990 Corvette. These are manufactured and welded in USA by Corvette Central (cases are manufactured in Canada).
On the original 1984-1990 dual-outlet muffler, the inner outlet tube is for appearance only, and is blocked off. With our design, the outer outlet tube is open, but the inner outlet tube is connected to a small diameter resonance tube. This design provides the correct sound and quietness of the original design without the annoying low-RPM drone.
Quote from CC's website: Corvette Central is pleased to introduce our exclusive correct sounding dual outlet mufflers for the 1984-1990 Corvette. These are manufactured and welded in USA by Corvette Central (cases are manufactured in Canada).
On the original 1984-1990 dual-outlet muffler, the inner outlet tube is for appearance only, and is blocked off. With our design, the outer outlet tube is open, but the inner outlet tube is connected to a small diameter resonance tube. This design provides the correct sound and quietness of the original design without the annoying low-RPM drone.
What Corvette Central did was put a resonance tube in one of the outlets. I'm assuming it still passes exhaust out that tube. So, I don't think they 100% blocked it off. This is the first I've heard of having a resonator in the muffler.
But I had put in some Walker mufflers a while back. And that got rid of the drone. I think they were the Quiet Flow.
Team Owner
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From: Athens AL
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Resonance is a characteristic of all exhaust systems where the engine RPM matches the resonant frequency of the exhaust system. All of them will resonate at different frequencies, yet some are not going to resonate at frequencies your engine can create or will resonate to varying degrees. Some may be so quiet so as to not be annoying. Sometimes thats because theres something inside to break up those pressure waves, which is what a resonator does. X and H-pipes do the same thing.
It depends on full exhaust length, diameter of the pipe, the flow ability at choke points like Y-pipes, etc. In general, shortening the exhaust piping raises the RPM with which resonance occurs at, lengthing lowers the RPM. If your engine never constantly runs at that RPM, then you've gotten around the problem. I believe thats how the Corsas do their magic.
It depends on full exhaust length, diameter of the pipe, the flow ability at choke points like Y-pipes, etc. In general, shortening the exhaust piping raises the RPM with which resonance occurs at, lengthing lowers the RPM. If your engine never constantly runs at that RPM, then you've gotten around the problem. I believe thats how the Corsas do their magic.
Team Owner
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
What do you guys think about putting one of the dynamax or magnaflow mufflers with two pipes in and out in the center where the resonator would normally go and then just run straight pipes to the rear, past the bumper cover? Do think this would help? Most of the muscle cars I've seen that have the mufflers in the center of the car don't have resonance.
Le Mans Master
Joined: Oct 2004
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From: Everett WA
C4 of Year Finalist (appearance mods) 2019
Resonance is a characteristic of all exhaust systems where the engine RPM matches the resonant frequency of the exhaust system. All of them will resonate at different frequencies, yet some are not going to resonate at frequencies your engine can create or will resonate to varying degrees. Some may be so quiet so as to not be annoying. Sometimes thats because theres something inside to break up those pressure waves, which is what a resonator does. X and H-pipes do the same thing.
It depends on full exhaust length, diameter of the pipe, the flow ability at choke points like Y-pipes, etc. In general, shortening the exhaust piping raises the RPM with which resonance occurs at, lengthing lowers the RPM. If your engine never constantly runs at that RPM, then you've gotten around the problem. I believe thats how the Corsas do their magic.
It depends on full exhaust length, diameter of the pipe, the flow ability at choke points like Y-pipes, etc. In general, shortening the exhaust piping raises the RPM with which resonance occurs at, lengthing lowers the RPM. If your engine never constantly runs at that RPM, then you've gotten around the problem. I believe thats how the Corsas do their magic.
Team Owner
Joined: Aug 2004
Posts: 21,543
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From: Park City Utah
I believe if you can get an H pipe in there, it would be a change, but it would be for the better. The colliding of the exhaust pulses is probably where most of the resonance is coming from. Actually, removing the X pipe, and making them true duals would be the best thing for resonance
You can read the whole thread HERE, and the actual posts HERE, here, here and the summary, HERE. For a chuckle, read the exciting conclusion, HERE.
Also, I don't believe about the muff's being close to the end of the exhaust; Mustangs, GTO's and CTS-V's (among others) have muff's right at the end of the system, and don't resonate as badly (as the C6 does at least).
I agree w/the guy that talked about the rear cargo floor. I've READ (but not tried) that putting dynomat on that area reduces drone enormously.
Last edited by Tom400CFI; May 26, 2010 at 05:56 PM.
Le Mans Master
Joined: Jun 2006
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From: One day you're a Comet...the next day you're dust... Arkansas
I introduced some irritating resonance in my 1989 when I eliminated the pre cats and went to dual outlet OEM style Magnaflows. It is only annoying between around 1200 and 1500 rpms and with a 6 speed I'm not in that range very much. I think it is caused by the dual outlet mufflers setting up a vibration.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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Resonance is a characteristic of all exhaust systems where the engine RPM matches the resonant frequency of the exhaust system. All of them will resonate at different frequencies, yet some are not going to resonate at frequencies your engine can create or will resonate to varying degrees. Some may be so quiet so as to not be annoying. Sometimes thats because theres something inside to break up those pressure waves, which is what a resonator does. X and H-pipes do the same thing.
It depends on full exhaust length, diameter of the pipe, the flow ability at choke points like Y-pipes, etc. In general, shortening the exhaust piping raises the RPM with which resonance occurs at, lengthing lowers the RPM. If your engine never constantly runs at that RPM, then you've gotten around the problem. I believe thats how the Corsas do their magic.
It depends on full exhaust length, diameter of the pipe, the flow ability at choke points like Y-pipes, etc. In general, shortening the exhaust piping raises the RPM with which resonance occurs at, lengthing lowers the RPM. If your engine never constantly runs at that RPM, then you've gotten around the problem. I believe thats how the Corsas do their magic.
I would add to Vader's explanation that the cabin shape probably adds to the engine rpm/exhaust length tuning effect. Because the rear of the couple is shaped like a cone (at least part of one, I suspect sound is "focused" back toward the seating area. Though I don't want to consider/compare it to a parabola, anything close to that shape could have a tendency for focusing sound.
My experience was similar to BADDUCK's. The removal of front cats, installation of 2.5" front "Y", and dual-outlet resonators caused a pronounced resonance at lower rpms. All I had to do was reinstall front cats (Magnaflow spun cats in my case) and the sound went from annoying to music.
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Team Owner
Joined: Feb 2006
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From: San Antonio Texas
What do you guys think about putting one of the dynamax or magnaflow mufflers with two pipes in and out in the center where the resonator would normally go and then just run straight pipes to the rear, past the bumper cover? Do think this would help? Most of the muscle cars I've seen that have the mufflers in the center of the car don't have resonance.
Just a thought
Just a thought
Sadly the Dynomax dual in & out muffler is just a bit too fat to fit under the Vette like the original resonator does.
Maybe some sharp muffler guy will fab up one similar that will fit under there and then use the 'muffler eliminator' pipes out the back. Then we'll know if that's the answer to the deafening resonant drone v/s good tone.
Thread Starter
Pro
Joined: Apr 2001
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From: Lenoir City TN
My original post of putting the single muffler in the location of the resonator then running pipes to exit at the original location would keep the noise from the muffler closer to the seat area, thus keeping it out of the coupe area. This I believe would help eliminate the resonance.
My current set up has Hookers to the magnaflow dual in dual out located at the resonator area out to two magnaflow mufflers at the original locations and I still have resonance at the 1100 to 1400 RPM range.
Do you guys think, based on the responses above, that my original suggestion may work?
My current set up has Hookers to the magnaflow dual in dual out located at the resonator area out to two magnaflow mufflers at the original locations and I still have resonance at the 1100 to 1400 RPM range.
Do you guys think, based on the responses above, that my original suggestion may work?
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
My original post of putting the single muffler in the location of the resonator then running pipes to exit at the original location would keep the noise from the muffler closer to the seat area, thus keeping it out of the coupe area. This I believe would help eliminate the resonance.
My current set up has Hookers to the magnaflow dual in dual out located at the resonator area out to two magnaflow mufflers at the original locations and I still have resonance at the 1100 to 1400 RPM range.
Do you guys think, based on the responses above, that my original suggestion may work?
My current set up has Hookers to the magnaflow dual in dual out located at the resonator area out to two magnaflow mufflers at the original locations and I still have resonance at the 1100 to 1400 RPM range.
Do you guys think, based on the responses above, that my original suggestion may work?
Team Owner
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From: Park City Utah
Le Mans Master
Joined: Oct 2008
Posts: 9,758
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From: Houston Texas
From what I have read from previous posts the corsa are not fully functional the outer tip is still there for a reason to release internal pressure from the cancellation chamber therefore canceling the resonance.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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My original post of putting the single muffler in the location of the resonator then running pipes to exit at the original location would keep the noise from the muffler closer to the seat area, thus keeping it out of the coupe area. This I believe would help eliminate the resonance.
My current set up has Hookers to the magnaflow dual in dual out located at the resonator area out to two magnaflow mufflers at the original locations and I still have resonance at the 1100 to 1400 RPM range.
Do you guys think, based on the responses above, that my original suggestion may work?
My current set up has Hookers to the magnaflow dual in dual out located at the resonator area out to two magnaflow mufflers at the original locations and I still have resonance at the 1100 to 1400 RPM range.
Do you guys think, based on the responses above, that my original suggestion may work?
If that dual-in/dual-out piece in your mid-section is a muffer or resonator, using it with straight pipes to the back will only make it louder. Resonance may change it's focal point though.
My first thought would be to put dual glass packs in the belly, leaving your Magnaflows at the rear. IOW, create a true dual config. (That solves the "Y" interaction spoke about in this thread. (The longer the glass pack, the quieter the result.)
Melting Slicks
Joined: Feb 2005
Posts: 3,204
Likes: 4
From: Midland Georgia
St. Jude Donor '06
"Resonance, where does it come from?"
My theory is this... C4 exhaust resonance comes from Hell!!!! First Generation B&B (Billy Boat) exhaust systems are the spawn of Satan. Couple the B&B with Long tube headers and a LT-4 Hotcam and drive for more than 45 minutes and your head will feel like Satan
: and all the members of AC/DC 
have moved into it. Ask me how I know!
My car still has the long tube headers and the Hotcam but no B&B. I switched it out for a factory exhaust and it purrrs at cruise and roars when I get on it...
Before you spend alot of money experimenting, aka spending tons of money, go back and search for old write ups here on the forum. You will learn alot and it will prevent you from repeating mistakes that others have made. Good luck!
My theory is this... C4 exhaust resonance comes from Hell!!!! First Generation B&B (Billy Boat) exhaust systems are the spawn of Satan. Couple the B&B with Long tube headers and a LT-4 Hotcam and drive for more than 45 minutes and your head will feel like Satan
: and all the members of AC/DC have moved into it. Ask me how I know! My car still has the long tube headers and the Hotcam but no B&B. I switched it out for a factory exhaust and it purrrs at cruise and roars when I get on it...
Before you spend alot of money experimenting, aka spending tons of money, go back and search for old write ups here on the forum. You will learn alot and it will prevent you from repeating mistakes that others have made. Good luck!
Last edited by jakers; May 27, 2010 at 12:39 AM.
Platinum Supporting Vendor
Joined: Feb 2004
Posts: 1,771
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From: Sawyer MI
I'm sure there are single outlet mufflers that have drone. My OEM mufflers had drone and they are single outlet. So, I don't think having single outlet alone gets rid of drone.
What Corvette Central did was put a resonance tube in one of the outlets. I'm assuming it still passes exhaust out that tube. So, I don't think they 100% blocked it off. This is the first I've heard of having a resonator in the muffler.
But I had put in some Walker mufflers a while back. And that got rid of the drone. I think they were the Quiet Flow.
What Corvette Central did was put a resonance tube in one of the outlets. I'm assuming it still passes exhaust out that tube. So, I don't think they 100% blocked it off. This is the first I've heard of having a resonator in the muffler.
But I had put in some Walker mufflers a while back. And that got rid of the drone. I think they were the Quiet Flow.
According to our designer, yes, that small tube in our new C4 muffler does enable some (minimal) flow between the muffler’s front (inlet) chamber and the second outlet. The small diameter tube is designed to function as a pressure relief/vent and reduces peak internal (muffler) pressure. That is probably a contributor to the reduced levels of drone that these mufflers provide.
The primary reason the mufflers sound “right” is that our new C4 muffler is identical in design and function to the original C4 muffler, including the tube diameters, chamber lengths and chamber volumes. The resonator function is built into the internal design of the muffler. A reverse flow pattern in the front section of the muffler is combined with a rear chamber that functions as an expansion chamber/resonator.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
I would add to Vader's explanation that the cabin shape probably adds to the engine rpm/exhaust length tuning effect. Because the rear of the coupe is shaped like a cone (at least part of one, I suspect sound is "focused" back toward the seating area. Though I don't want to consider/compare it to a parabola, anything close to that shape could have a tendency for focusing sound.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
What do you guys think about putting one of the dynamax or magnaflow mufflers with two pipes in and out in the center where the resonator would normally go and then just run straight pipes to the rear, past the bumper cover? Do think this would help? Most of the muscle cars I've seen that have the mufflers in the center of the car don't have resonance.
Just a thought
Just a thought
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Does anyone have any pics of an LT1/4 muffler cut open like the corsa muffler? I would love to see the difference? How about the center resonator?
Maybe if we get as many pics of mufflers cut open and peoples experiences we can see what could possibly work...
I think the Vettes shape, the material it uses (fiberglass), the engine tune/gears, and the location of the exhaust have to also do a lot with the resonance. Maybe if the pipes were separated they wouldnt act as tuning forks. I am not sure, just throwing some ideas out there.
Exhaust flow has a lot to do with it because when you add restriction it usually cuts down the resonance. Like stated above its probably caused by sound waves cancelling but if that is so then how do you make a free flowing muffler that is low on resonance?
Maybe if we get as many pics of mufflers cut open and peoples experiences we can see what could possibly work...
I think the Vettes shape, the material it uses (fiberglass), the engine tune/gears, and the location of the exhaust have to also do a lot with the resonance. Maybe if the pipes were separated they wouldnt act as tuning forks. I am not sure, just throwing some ideas out there.
Exhaust flow has a lot to do with it because when you add restriction it usually cuts down the resonance. Like stated above its probably caused by sound waves cancelling but if that is so then how do you make a free flowing muffler that is low on resonance?