OK, I know this has been beaten like a rented mule, but is it generated in the mufflers themselves? If so do to our mufflers being in the back when it comes thru the floor in the coupe area it is reflected off the hatch glass and is then radiated into the rest of the cabin.

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

 

Resonance in the C4 is definitely a problem... I wish I had the answer.

 

Well if you remove the mufflers and just run the reonator amounts to the same thing more or less....I am running the B&B 3 inch system and removed the mufflers.....too loud to hear any resonance

 

I had flow masters and the resonance was bad.
Then I went to these: http://forums.corvetteforum.com/c4-t...te-videos.html

 

War...what is it good for?

 

Absolutely nothing.

(C'ept population control)

 

So if the pipes exit closer than an inch from the further most part of the body.

If the muffs have dual outlets.

Look at the OEM & Corsa's. Only one tip works, least amount of resonance......

 

More than one tip works on the Corsa. I don't think tips are the key. It has to do with the design IMO.

 

essentially, it is the sound waves pushing each other in the Y pipes. Theoretically, if the Y pipes are of different lengths in the Y, you can tune out the pulse bumping, and get great sound.
Ever see the pipes on an LT-1 corvette?
There is a chamber in every muffler called the helmholz chamber. in it, the chamber is a dead end, and only has one door for the sound waves to go through.
The exhaust sound wave goes into the "room", bounces off the far wall, and heads back out to the door.
WEll, wouldn't ya know it, here comes another sound wave!!!! Bam, they crash into each other, at the same frequency, same sound level, and cancel each other out. The only thing left is gas pressure, which then bounces around a lil, pressurizes the room, and heads out the door to the atmosphere.
That is how a muffler works.
For instance, if you put an H pipe into a y pipe, it cancels out the resonance because it diffuses the power pulses in the pipes by giving the pressure an alternate path just before the next sound wave comes sliding through the pipe..then the pressure wave is pushed back into it's own bank's pressure flow, and the sound wave is tumbling, and diffused.
I have an H pipe, dual cats, true dual exhaust, and 91 convertible mufflers. There is a buzzing in the pipes when you sit in the driver's seat. outside the car, it is a mellow tone.
Inside, you can hear the radio all day long.

 

I have an X-pipe on my car, no cats, and magnaflow mufflers. The resonance is pretty bad at about 1800 RPM. Would an H-pipe instead of an X-pipe help?

 

Wont make a difference. Problem imo( no scientist here) with C4 systems is they are short and theres nothing after the muffler. Remember when guys would take a fairly stock car with a full exhaust then cut it off after the muffs and put turndowns on them? Effect is kind of similar. coupeguy brings up some good points fwiw.

 

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.....I think you would only notice a minor power change at upper RPM ranges.
It is interesting to note, that I have a friend with a pickup that was dropped down to about 2 inches off the pavement, and the resonance was so loud that the dashboard buzzed.
He put it back up to stock height, and did nothing else, and the resonance went away completely.
Like night and day.
He has Walker mufflers, dual cats, and stainless aftermarket pipe. Interestingly, the cats are on equal length pipes.
You can also try something else.
Try closing off one tail pipe on each muffler. Use a large round wooden dowel if you can find one. if not, make one by using copper pipe, and soldering a cap on it. (just realize, if you leave it there, it may get hot enough to melt the solder, and the cap will fall off, so just go around the block, or down the street and back.
If the resonance goes away, the sound waves are crashing in the mufflers, and not the X pipe.

If the resonance goes away, try getting a copper pipe cap and pushing it into one pipe, closing off one tailpipe completely, drilling a 1/2 inch hole in it. keep making the hole larger until the resonance comes back, then go back to the last size drill before the noise came back.
See if you can thread the cap with an allen set screw, and set the caps in one pipe on each side so they won't come out with the curved side in, recess out.
Then, with that stuck in one pipe, the pipe will turn dark because exhaust is flowing, and the resonance will be cancelling out the power pulse frequencies, and the tail pipe that the exhaust is coming out will probably be the same size as your actual exhaust pipe ahead of the muffler.
Give that a whirl, and see what happens.

 

A friend has a set on his ZR1. Only one tip works.

So I experimented with my Borlas and blocked one tip.
Resonance was reduced significantly.

 

Corsa works because there are special sized chambers in the muffler that change the frequency of the sound...

 

Regarding Corsa mufflers and what's inside em and why they are the way they are .... some of you may be interested in these two posts from back in 2005

Some of you may remember jeffvette from the Zr1 forum. He is the one in the first post who actually cut open a corsa muffler. In the 2nd post is the answer that the folks from Corsa sent back to my query

http://forums.corvetteforum.com/c4-z...a-muffler.html


http://forums.corvetteforum.com/c4-z...rom-corsa.html

 

I rest my case.

 

Corvette Central has come out with some no drone mufflers for the C4.

 

A lot of good info on helping the problem above, but like cruisinartvette, I think it's inherently because the Mufflers don't have enough Tailpipe on them. Back in the 60's I cut the Tailpipes off my SS Chevelle and the thing buzzed the whole car at certain RPMs. I added some "Turndowns" ; about 12" long with a 5-6" downpipe; and it stopped...

 

A few years ago I was fooling around with thin sound damping matherial in the hatch area. While the carpets were up I noticed that the floor panels really vibrate at around 1600-1800rpm. It seems that the resonance is mainly due to these panels acting to harmonically resonate with the exhaust noise; at least that's my thinking.
If ture some way of damping out those panels would do the trick to eliminate resonance in our C4s.

 

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.