True or False?

[compyelc4]

I usually ride the C4 side of this site, but we have a good question going around in our Vette club. Any of you C5 types know the answer to this one? .....and if you answer is "yes", can you back that up! I'm not trying to "shout", below. I've just copied an e-mail post from our club pres.

> ON C-5'S---THE EXHAUST SYSTEMS ARE DESIGNED DIFFERENTLY---SO THE EXHAUST ON THE ROADSTER IS QUIETER FOR "TOP DOWN" OPERATION.
>
> IS THAT SO--OR IS THAT JUST ANOTHER SELF PROCLAIMED CORVETTE EXPERT BLATHERING ?
>
> IF TRUE---I'D LIKE TO HAVE A REFERENCE

Thanks folks.

 

[ironcity]

Sounds like a question for the c4c5 specialist...:confused

 

[Justin_cv87]

hmmmm... I would guess no, its false, because that would be confusing, having 2 different exhausts for the same year car. people that dont know much about what they are driving would buy the wrong one, but if it is true, id get the louder one even if i had a vert!

 

[cntrhub]

The convertable top Vettes have weak chassis integrity. They over-flex. Hard tops on the other hand, act as a "stress member." Therefore, the convertables undercarriage is beefed up and different exhaust plumbing needs a slight redesign.
I am no expert, but I remember something about this being mentioned in a new model seminar.

 

[Edmond]

I usually ride the C4 side of this site, but we have a good question going around in our Vette club. Any of you C5 types know the answer to this one? .....and if you answer is "yes", can you back that up! I'm not trying to "shout", below. I've just copied an e-mail post from our club pres.

> ON C-5'S---THE EXHAUST SYSTEMS ARE DESIGNED DIFFERENTLY---SO THE EXHAUST ON THE ROADSTER IS QUIETER FOR "TOP DOWN" OPERATION.
>
> IS THAT SO--OR IS THAT JUST ANOTHER SELF PROCLAIMED CORVETTE EXPERT BLATHERING ?
>
> IF TRUE---I'D LIKE TO HAVE A REFERENCE

Thanks folks.

Not totally sure of the C5, but I know for a fact that some C4 convertible models did have 5 less HP rating because of the slightly more restrictive mufflers for keeping the decibels low.

I wouldn't doubt that the C5 takes the same theory into the design of the mufflers.

 

[c4c5specialist]

Hi there,
Well, I have never heard of that one before, very interesting.
I will tell you what I know. And what I will have to check on.
The actual c5 body and frame design was originally designed as a convertible first, and not a coupe. Unfortunately, with the c4 design, noone ever thought that there would be a convertible. Therefore, when body structure and noise were being analyzed, they found that once the rear B pillar, or roof rail behind the seats was such an integral part of the body structure, they had to use alot of extra frame strengthening to get it somewhat better.
On c5, this is not the case. frames are exactly the same in coupe or convertible, or hardtop. The difference are in the actual body that is mounted on the frame. There are not alot of people whom actually know that the hardtop in ZO6, is actually just a simple panel, which is bonded to the windshield frame and rear B pillar. When convertible came in to the line in 98, the structural frequency was actually within 5 hz of the coupe, and actually better than the SL class Mercedes, and many other convertible car lines.
As for the muffler assemblies, I do not know, and will research this while at work today. I do know that there is more sound deadening material in convertible than coupe, in the rear trunk area and side storage areas.
The attached is the actual frame dimensions, for correct frame repair on c5. This is the same for all 3 models.
I will repost this evening for correct muffler part numbers, and expaination.
Allthebest, c4c5

 

[Edmond]

Okay, I read the thread from the CAC which states the restriction on convertible mufflers for sound reasons:


http://corvetteactioncenter.com/specs/c4/1988/index.html

It's all the way at the bottom.

 

[c4c5specialist]

Hi there,
Ok, update here, on the muffler designs.
Now, there is no difference in muffler designs for body styles.
We will attempt to look at it from an emissions point of view, and then, you will find changed in the muffler designs.
If you have an export car, there are different muffler designs, for this emissions package.
For California emissions, there is different muffler designs.
Then, for federal emissions, there is a different part number.
It is not chosen by body designation, only emissions package.
For example, if you have NC1, which is California emissions, then 12455779 for the left, and 12455778 for the right muffler.
Export emissions, NP1 as I recall, 88895873 for the left, and 88895874 for the right..
so, with that, I hope it answers your questions, all thebest, c4c5

 

[99WhiteC5Coupe]

c4c5specialist,

You stated that the C5 convertible has more sound deadening material than the coupe.

I am not happy with the noise level in my 1999 C5 coupe (with the top on). Is the sound deadening material something that I can order/buy from my dealer and add, or is it sprayed on when the car is assembled?

I have already added jute underlayment (purchased from my dealer) under the rear hatch area carpet, and under the carpet on top of the wheel wells. I also have a carpet mat on top of the rear hatch area carpet.

Thanks.

 

[c4c5specialist]

HI 99,
Well, I do a few things to assist in the interior noise department.
What you have already done helps some, however, there are no coatings given in the assembly plant that reduce noise.
As for what I do, there is a matting, kind of like A NOISE MATTING, that sound system installers use.
The part number escapes me for now, however, I will check on that on Monday, because I am off for the day.
So, with that, just remember, the stuff that I use will bond directly to the rear tub fiberglass, and cannot be removed without a great deal of work.
If that is ok with you, I think you will be pleased with the results.
Allthebest, c4c5

 

[JBsC5]

Could the california noise emission standard be tougher and thats why?

 

[99WhiteC5Coupe]

c4c5specialist,

Thanks - I have seen a variety of posts with people using "Dynamat", a mastic sheet that dampens sound. If you have a GM/Chevrolet part number - let me know. I will order it through my dealer.

What are the best places to use the mat to reduce sound? I don't want to install it in places that has little or no effect.

Thanks again.

 

[c4c5specialist]

HI there,
JB, you are exactly correct, as CARB research decible levels are different, so in conjunction with the emissions standards, also toe the line with noise standards.
99, honestly, it really depends on what type of noise you are attempting to deaden. Some people do NOT like the road noise from the tires, others dont like the exhaust resonance with the aftermarket mufflers.
Road noise, normally, I add the matting to the wheel house area, behind the speaker assemblies, and the floor, underneath the mounting pods for the removable top.
Exhaust noise, I will add to the rear tub assembly, which is a totally one piece design. Critical there, is the rear storage areas, and the back wall of the trunk, facing the rear lights, up to the latch mechanism.
Recorded drops of 6 decibles I have measured using this technique.
I hope that this helps, c4c5

 

[99WhiteC5Coupe]

c4c5specialist,

Thanks for the information.

I do NOT like the Goodyear EMT tire noise - it seems to have become louder as the tires wear. The exhaust noise is fine - I have the factory exhaust.

 

[JBsC5]

Those Goodyears can certainly get loud as the miles roll on thats for sure..

I heard the other runflats that are out..by other manufacturers don't go 200 miles @ 55 mph and thats why they are quieter when properly inflated..I think they are good for 50miles when they go flat..

You might consider switching tires as well.


The goodyears are quite old runflat technology..

The new michelin pax system to roll out on the C6 requires new wheels but it supposed to be even more impressive.

On my last C5 when I went to non runflat michelin pilot sports I was amazed at the difference in the car..

If I was annoyed by tire noise..like you..if youv'e gotten decent miles out of them..I'd probably consider the new Yokohama or Michelin runflats(non pax system but runflats that fit on our wheels) that are out..

Once you switch..its amazing..

Might just solve your concerns..

 

[Edmond]

JB,

Those are good points you make about the runflats. With almost everyone having a cell phone, do you really need runflats? Plus, you could always get one of those fix-a-flat thingies that comes with the Z06's right?

It also depends on where you drive. If you're driving along dessert roads, I wouldn't ditch the runflats. But if you were driving along roads where you can safely get help, I'd switch those runflats out of there.