89'Bowtie

I made a mistake of making a 3 inch dual system on my Corvette. I did not want to reduce and step up/down from my SW headers to the a center resonator, and them into 3 inch mufflers. Result, large system with large drone.

System consists of:

SW headers --> Lead pipes --> 3 inch cats --> 3inch In/Out Dual Magnaflow resonator --> Magnaflow mufflers

The drone is an acoustic issue. The stock system uses a resonator as you all know and muffler with some form of chambering.

I've stuffed steel wool in 1 outlet of each muffler and the exhaust drone goes drastically down, however it keeps blowing out and chocks the exhaust. However doing that creates a chamber for the sound waves to travel and cancel out eliminating the drone.

Everyone knows the drone happens on the C4's with soo many systems.

I was proposing to replace the center resonator withe a Flowmaster 40 series to see if the chambered unit would elimate the drone.

Has anyone ever done anything like that? Use a chambered mufflers as a resonator. Flowmaster makes a dual in/dual out 40 series unit.

The G8 community was experiencing high drone on their cars and they came up with a "j" shaped pipe off each muffler inlet to capture the sound waves and eliminate drone. With straight though systems the, the sound waves are not cancelling out anyone or in any chambers and we get that annoying drone. Their drone was at the 100-120 hz band and they calculated a sound wave length of 26-29 inches which dictated their J pipe length.

http://www.g8board.com/forums/showthread.php?t=28831
http://www.performancecarweb.com/showthread.php?t=144

I cannot afford a Corsa system, so it's come down to DIY and experimentation.

Anyone have any feedback or input or experience with drone efforts of their own.

Vic

leesvet

if you are willing to do some welding, the science behind this is not difficult at all. All that is necessary is a chamber/place to interrupt or disrupt (in this case) the natural pattern of sound wave without hindering the gas flow...easy enough.

Build a box or rectangular section and weld a couple solid baffles inside it so that the route thru is like a zig zag maze....sound waves are not good at following square shapes and sharp corners. Like any wave form its round...curved as it travels and expands with distance.
As they are deflected off one 'baffle' and routed to the next the wave pattern will be broken dramatically even tho the gas flow is maintained.

Your wad of steel wool does the same thing just in a different way...its breaking the pattern up by diffusion...same end result.

You can also contructs a round chamber that allows the wave to enter but it is forced thru the only exit that is back thru a tube that has many holes in it so the gas keeps moving but the wave has to do a 180 to get to the exit. This is a tube welded inside the 3" exhaust tube...or even a larger tube to keep flow up.

Anyone with 2 stroke engine building/racing experience can tell you about sound waves...the shape of the exhaust chamber is the key. The ONLY difference is the exhaust valves that stop the header from deep scavenging the cyl head. Besides that, the principles remain the same.

Break the wave pattern and you're back listening
to the Bee Gees...

coupeguy2001

I have been through the gauntlet with my 86 exhaust.
1. First, stock exhaust with custom abarth mufflers.( got from a dissatisfied owner) lotsa drone........
2.THen, I tried making muffler "hats" for them with the hats pointing down, attached with really long clamps. They deflected some noise down. Helped a little.
3. THen I got the idea that my catalytic converter was the noise problem, and bought a cat from Summit......one word.......LOUD. I went back to the factory cat.
4. I got some1990 convertible mufflers. They were much better on the drone. (apparently, by 1989, enough people had complained, that GM did some research and produced these mufflers for the cloth top folks. The drone was really subdued.
5. I had determined that with my original cat reinstalled, the precats might be a plug, so I got an 85 front Y pipe, (no precats) and installed that with the original cat. My car seemed much better on acceleration, but the gas mileage had begun to fall off.
6. I removed the factory exhaust manifolds, and ported the inlets to them. Now we're talkin'.
The car seemed to regain the low speed power, and more power at about 1700RPM going up a steep hill at 75.
7. I have a friend that suggested I buy a fabricated true dual system that he had hanging in his spare parts bin.
I installed his true dual exhaust with dual cats, 1990 mufflers, and the car really picked up some HP.
8. I decided to install some bullet cats in place of the cats that were installed.
Upon removal, we found out that the cats were gutted.
9.Well, since we torched em off, I just installed my bullet cats. I lost a little mid range.
So, I ended up wth a true dual exhaust with ported exhaust manifolds and 1990 vert mufflers, and no drone.
What I found out:
A. THe front Y pipe, dumping both exhaust streams into the cat causes the drone.
B. There was a vain attempt at the factory to minimize the drone by putting the precats at different lengths from the exhaust manifolds. (check out an LT-1)
C. The 1990 mufflers have a 1/2" hole in the "blanked" side. This blanked side has the hole attached to a heimholz chamber in the muffler to inject pulses into the exhaust stream at higher velocity, negating the muffler noise pulses.

I am getting too old to jack this thing up every day and play with the exhaust. The exhaust burbles, The 383 makes it scoot, and the paint shines. what more could I ask for?

Midnight 85

Oooh so true. I put 6 different exhaust combinations on mine before I settled on a pair of universal Magnaflow brushed stainless muffs. Still a bit loud but at least I can hear the cd's. I'm done changing muffs, for the same reason as you.

ZRWHAT

I just installed a home made system on my ZR-1 and it has no drone and is very livable sound wise and you can carry on a conversation at almost any speed except half throttle on up. I went with a set of Dynamax VT 3" mufflers, full 3" system with a 3" X pipe right off the headers without cats.

Very civilized around town and at most reasonable speeds, Really growls once the spring loaded valve opens fully to allow a full 3" flow through the entire system.

Got my best price on the net than called Summit racing who price matched and even knocked off a few bux and free shipping.

Used a set of Corsa Clone 3" inlet tips welded to the Dynamax's.

Whole system is stainless including the mufflers. Had a local shop who does Mandrel Bending make up the pipes for me and even made the X pipe.

Entire system cost me just about $850 and I like it much better than my 3" B&B on my other car.