I went ahead with the flowmaster 40 series, knowing full well they will resonate. My case is no different, thankfully at reasonable highway cruising speeds, it is minimal. I personally do no mind, I even like it since it generates so many stares where I got none before, however, I know my girlfriend will not think it is so cool.

My question is has anyone tried to address this by putting sound deadener on the hatch floor? Seeing as though it is just a thin piece of fiberglas, has anyone tried putting down sound deadener (like dynomat or tar paper) with any success? It seems to me if that was dampened, a large source of vibration would be eliminated.

 

I have an older C4 but I have the muffler eliminators and 0 resonates. Maybe just a tad in the morning before the cats warm up. I think I owe it to the double carpet padding on the rear floor (I left to original carpet and padding on the floor and put the new carpet right over that) and the tips being 3-4 inches past the bumper (see my sig). Just dumb luck from the muffler shop when the Mid-Am kit wqs installed. And the installer cut them back about 3 inches from where they would have been, he said.

BIG JIM

 

First, sound deadener will help you live with it, but it'll still be there. I found a good deadener that's as good as Dynamat Extreme, but much cheaper. See my web page at: http://temp.corvetteforum.net/c4/gh86e/index4.shtml

When I bought the car, it had another performance exhaust, but little resonance. It had a crossover tube on the 'Y' pipe that goes between the cat and the mufflers. Others on CF have said that helped reduce the resonance. I currently have Power Effects, which doesn't have that Y, so I couldn't go to that solution. Mid-Am, Ecklers, and such, sell the 'Y' pipes with crossovers (Walker is one brand).

Another CF'er, who had a nearly identical setup as me ('86 with Power Effects) said that the resonance went away when he installed large tube intake runners. It apparently changed the air flow through the engine resulting in different sound characteristics. It was the only thing he changed, and the resonance went away doing that. I'm still thinking about that one. I'd rather spend money on a new ZZ4 then upgrading my 110k current engine.

Some CF'ers have said that if the end of the exhaust is short of the back of the car, then that increases resonance (the exhaust sound resonates up under the rear of the car). That's not my case - my Power Effects tips extend to the full rear of the car.

When I installed the Power Effects, I also installed a Random Tech high-flow cat. The car was unbearable to drive for more than 15 minutes (the resonance is in the 1900-2100 rpm range, which with a 4+3 and 3.07 rear means that on the highway, I was always in 1900-2100 rpm range, and thus max resonance). I gave the Random Tech cat away, and reinstalled a new stock cat, and some of the resonance went away.

From my web pages, you can see I installed 2-3 layers of the sound deadener throughout the interior (incl. console sides and floors). I also installed very heavy new carpet - thicker-than-stock carpet ('Custom Comfort' material from 1aauto.com), with heavy 'mass' backing. So with all the sound deadener (about 50 pounds worth), the heavy carpet, and the stock cat, I now have a car that I can stand to drive, but I still would hesitate before taking it on a highway drive of more than 2-3 hours.

Gregg

 

I thought you could adjust the power effects to sound like stock mufflers :confused:

 

On my new setup I have no resonance, I have a 3" pipe in place of the cat and I think that made the difference.

 

Everything I said is with Power Effects at the quietest setting. Now you open them things up, and it gets much worse. I never use any setting other than the quietest (and it certainly is NOT stock). The documentation nowhere says that at the quitest setting it is the same as stock - it says the airflow is the same as stock. I like the PE's, and will keep them. But I was hoping for an exhaust that i could keep at a quiet setting weekdays (like when I leave for work at 5am), and open it up on weekends. No way. It's noisy (but nice) all the time, even at the quitest setting. BTW, other users, and the PE manufacturer confirmed, that PE's get louder after a few months of use (the sound absorbing material packs down or something like that). I think they did, but can't say for sure.

 

How do you change the settings on the Power Effects? Do you get out and throw a lever or is there a switch inside? Do they rattle?

 

On each side 'capsule' (muffler) there's a big round aluminum ****. You can reach down under each quarter panel and turn to the **** to one of six settings. PE's are essentially straight-thru tubes, each with an outer chamber. There's a butterfly valve at the end of the tube. You leave it horizontal (fully open), and you have straight-thru tubes. Any of the other 5 positions closes the valve partially or fully, forcing some/all exhaust to go through the outer chamber, which has sound deadener material. The ***** are easy to turn, even when the car is hot (but difficult to do while your're traveling at 70 mph :) )

Do they rattle? No. PE's are very well built - very solid materials and construction. One of the few things I've bought over the years that are well made.

BTW, as far as the noise level, the president of the company said half the users complain they are too loud, and the other half complain they aren't loud enough.

 

How do you rate the resonance at highway speeds, open vs closed? Can you hear the radio?

 

Only ways to really effectively reduce resonance is crossover pipes and extending the tips of the mufflers past the bumper.

With the tips right under the rear, youre just creating a big sound chamber in the back. Dynomat helps some, but it wont get rid of it.

 

The dynamat is heavy, adds weight, and is a pain to install. It doesnt fix the problem either.

I have been fighting resonance since I bought the car. THis is what I have learned:

1. Removing the cats and resonator makes things A LOT WORSE!
2. A crossover pipe in your Rear Y Pipe really doesnt help much.
3. Extending past the bumper helps a little.
4. Secure, sturdy, vibration free mounting hardware helps.

And the number one and only effective way to stop reonance......

Block one of your muffler exits. The stock exhaust is that way, one is only for looks.

I think my next set of mufflers may be some Magnaflows with those big single exits.

Test it, you will verify the results.

 

Yes, sound deadener is heavy. But it just means I can now justify getting a 383 stroker :) No, it does not fix the problem. Yes, it does help live with the problem (and hear the radio). It did make the difference for me as to whether I kept the Pe's or not.

If you want tips on installing the sound deadener, email me. The biggest tip is to do it on a hot sunny day (I'll explain why if you're going ahead with this).

Gregg

 

Corsa's.

 

Actually weather permitting, rolling down the windows works pretty good.

Or keep your rpm's up. With my 4.10's the car gets real quiet above about 75mph in 6th gear.

 

I have heard an X pipe helps resonances as well.

 

I did it and it works for me! :steering:

 

I had a Flowmaster cat-back exhaust installed on mine last summer. I did get more noticeable resonance. Fortunately, it's a sunny-day driver and I can put up with it. However, I just had the new intake installed on it (see sig) and I have to agree that I don't notice the resonance like I used to. Now, here's the kicker. I'm picking my car up tonight from the guys installing the long tube headers. With any luck, I won't gain the resonance back. Keeping my fingers crossed :smash:

 

[QUOTE]Only ways to really effectively reduce resonance is crossover pipes and extending the tips of the mufflers past the bumper.

With the tips right under the rear, youre just creating a big sound chamber in the back. Dynomat helps some, but it wont get rid of it.[
/QUOTE] My tips are beyond the bumber and I have the cross over tube installed at the back the cross over helped a little but not much.
I have tpis long tubes three inch pipe no cats I have RESONANCE
Best way to make it better notice I said only better is drive at high speed just tell the nice officer that you were just trying to get rid of the resonance

 

:iagree: :iagree: :iagree:

 

Please post the results of your header upgrade. I'm interested in how much louder it gets and what changes in resonance occur. Thanks!

Gregg