Resonance

[CharlesBrown]

I've searched and found lots of very deep discussion on this subject. Too deep for me. I'm thinking about buying a replacement exhaust pipe for the '88 C4 i.e., the one with the balance tube close to where it fastens to the mufflers. The idea , of course, is to reduce the @#$&% resonance in the cabin. If you have used one of these I'd sure like to hear from you. Basically, how well did it work?

 

[6 Shooter]

CB - I highly recommend Corsa for their awesome sound and noise canceling technology!

C4 Corsa Performance Exhaust Products ​

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[CharlesBrown]

I believe you. But I've already spent quite a few $'s on a Borla system and an other $1500 or more... no, I don't think so.

C4 Corsa Performance Exhaust Products

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[Curious George]

I believe you. But I've already spent quite a few $'s on a Borla system and an other $1500 or more... no, I don't think so.

C4 Corsa Performance Exhaust Products

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So what exactly is your issue? Resonance obviously, but what is causing it / what exhaust do you have now? I take it Borla? Do you want an OE sounding exhaust with no resonance, but slightly louder?

CG

 

[geekinavette]

Extending the exhaust tips past the rear bumper can go a long way towards reducing in-cab resonance.

 

[JohnGrawcock]

Get the tips out past the bumper and consider adding insulation to the cargo area.

 

[Scottsredvette]

Extending the exhaust tips past the rear bumper can go a long way towards reducing in-cab resonance.

Bill, you feeling ok? A one line answer just isn't you:L

 

[geekinavette]

Bill, you feeling ok? A one line answer just isn't you:L

No I'm not myself lately huh... ;help

 

[GerryLP]

I believe that the specific resonance level is created by the engine at a particular engine speed, so the only way to attenuate it is by engineering controls. For example, I used to operate the GE T58 helicopter engine, and there was a point in its operating RPM where it was identified as a resonance range, and to avoid prolonged effects of resonance, we definetely made sure to transition that range as quickly as possible. Thus, since that resonance frequncy is causing the muffler system to resonate in the cab, it may be a ssimple as replacing an rubber insulator (a muffler hanger), or perhaps adding support to the muffler system. Often these aftermarket system do away with hanging points from the exhaust, and this often creates vibrations or amplifies the resonance level.

GerryLP :cool

 

[Hot Rod Roy]

Corvette Central has come out with some C4 "No drone" mufflers.

I installed the Corvette Central '84 mufflers (with turned down tips, like the originals). They advertise the sound as being just like original. The drone was terrible! They exchanged them for the '85 style, with longer straight tips. The drone is a little better, but is still considerable. My burned-out Dynamax were quieter! This C-C system even includes the cross-over tube in the rear Y-pipe, which the Dynamax didn't have.

confused

 

[Curious George]

I deleted the resonator (replaced with straight pipe with H-crossover) from my '92 convertible and kept the stock OE mufflers w/ square tips. The exhaust note has the same sound only slightly louder and NO resonance at all. The OE mufflers are very free flowing, so there is no performance penalty.

Just FYI -

CG

 

[Hot Rod Roy]

What exact mufflers did you try? As CC sells different mufflers and just came out with the "No Drone" mufflers. So, I'm unsure what exact mufflers you had installed?

I have the CC #324315 mufflers and the 324416 rear Y-pipe. I have also installed straight stainless tips on the four pipes to extend the exhaust even with the bumper cover.

 

[Rogue]

I went through two different exhaust systems for my C4. The factory exhaust is the quietest and has zero resonance because it only has ONE working tip per side. This is THE secret to no resonance on a C4.

I also used the y-pipe with a center connector on aftermarket mufflers....no difference in resonance. Later I had sound deadening material put on the cargo area.....very little difference in resonance. It did improve the interior road noise but the resonance did NOT go away.

I finally went to a Corsa exhaust. Not only does it look best, it is as quiet as stock at idle and absolutely zero resonance. It too has only one working tip per side. The other tip is a dummy for looks. However, it sounds beautiful when you stomp on it!

Borla is known to be one of the louder C4 exhaust.

Go ahead and spend the $$ on it. It's worth it.

Why not? Look.....

 

[Curious George]

I went through two different exhaust systems for my C4. The factory exhaust is the quietest and has zero resonance because it only has ONE working tip per side. This is THE secret to no resonance on a C4.

I also used the y-pipe with a center connector on aftermarket mufflers....no difference in resonance. Later I had sound deadening material put on the cargo area.....very little difference in resonance. It did improve the interior road noise but the resonance did NOT go away.

I finally went to a Corsa exhaust. Not only does it look best, it is as quiet as stock at idle and absolutely zero resonance. It too has only one working tip per side. The other tip is a dummy for looks. However, it sounds beautiful when you stomp on it!

Borla is known to be one of the louder C4 exhaust.

Go ahead and spend the $$ on it. It's worth it.

Why not? Look.....

On my '92, the OE exhaust had the large square tips (one each side). In my opinion, the lack of resonance in the cabin is a function of the mufflers tips extending out from underneath the car (like from the factory) and the muffler construction / design. I am sure GM spent considerable time designing the OE mufflers, so there would be no resonance inside the cabin.

Shortly after I bought my '92, I purchased the Corsa cat-back and initially, I was happy with it. No resonance, quite at idle, etc. In time, I did not care for the way it sounded and sold it to a friend with a '96 CE.

CG

 

[Rogue]

I understand your feelings about the Corsa.

It's a very high quality product that looks great. But it is not designed to be loud at all unless you are at WOT. Whenever I go to Cars and Coffee and see all those bad-ass cars, most of them have really loud exhaust. A favorite thing to do is people line up and watch all the cool cars drive home and the loudest ones get the most attention. The quiet ones, like my C4 get the least attention because it sounds like it is whispering along compared to others.

Where I live though, we have tons of moto-cops using LIDAR and they love collecting revenue. So quiet is a good around here. Some hot cars, you can hear them coming a corner or two away and you can tell when they are gunning it. If you were a cop, you'd be ready to pounce. No thanks. I'll take quiet and sneaky any day. Plus, when I go on long trips, quiet is king. I've had the loud and droning and it really takes away some of the pleasure on long trips.

 

[CharlesBrown]

Problem solved. Well almost, it's now almost quiet inside the car. Thanks to one of the posts in this thread, I simply blocked off the inside exhaust tips... The reduction in resonance is truly amazing. My technique (two tennis balls and duct tape) could not be viewed as elegant, but it worked! Next step will be to find a less obvious and more permanent solution.
ps Idle revs down maybe 75 or 100 too.

 

[Bobsvette]

Tennis Ball's, Duct Tape????? W T F.?:bash

 

[TedC]

My 1989 with the optional 3.08 came from the factory with both tips working. GM mufflers used on standard rear axles L98s and all rag tops used only one open tip. I've since replaced the stock mufflers with super-c mufflers from autozone. Both tips are open. Having the extra tip open adds 5 extra HP based on GM's ratings. No resonance. Tips are in the stock position and do not go past the rear bumper. Walker mufflers have both tips open. However, one tip completely open, while the other had a plate with a 1" hole. All of my research pointed to Corsa offering the best CFM flow with excellent sound management.

 

[CharlesBrown]

Tennis Ball's, Duct Tape????? W T F.?:bash

If WTF is a question regarding my approach to the “resonating” problem… let me explain.

1. IT WORKED!
2. IT WORKED AT NO COST!
3. Knowing the solution to the problem (as stated in my thread) I can now pursue a more elegant approach to closing one tip on each muffler

 

[John Robinson]

I like your approach with tennis balls and duct tape. Very ingenouis way to find out if your mufflers with 2 open pipes were part of the resonance problem. I also noted that someone said there mufflers had 2 pipes but one had a restrictor in it with a smaller hole for the exhaust. You might want to go to the hardware store and pick up a couple of stainless shower drain covers. Cut them to fit the pipe leaving about four tabs to bend to hold them inside the pipe. This might reduce the resonace and still allow the muffler to have less back preassure. I think (Only my opion) that what is happening with two outlet pipes is that the sound wave frequency from them being side by side is bouncing off each other causing the resonance. By putting a size restrictor in one pipe you change that frequency range on that pipe and the sound waves no longer interact with each other causing resonance.