"Resonance" Rice Noise?!? HELP! - Pontiac GTO Forum
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post #1 of 11 (permalink) Old 04-30-2012, 06:17 PM Thread Starter
 
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"Resonance" Rice Noise?!? HELP!

I have hacked and whacked my exhaust and I am getting frustrated! HELP!

On my 2005, I started with simple magnaflow stainless catback. It sounded good, but I wanted a little louder. Went with pacesetter long tube headers and the cat eliminating pipe after the headers, and WHAM! I had this exhaust "resonance" as the local speed shop guy calls it that sold me the headers. I have heard it on a few of the car sound bites that I have heard on the site. It sounds like a vibrating back pressure when you let off the gas or push the clutch in to shift. Sounds like a cherry bomb, sort of? And it is not vibrating on anything. It is strictly sound noise...sounds sort of like those fart can pipes they put on Hondas, etc.

I have since hacked and chopped and even tried my stock exhaust back on, and still have this "resonance" issue. Does anyone know what I am talking about?
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post #2 of 11 (permalink) Old 04-30-2012, 08:55 PM
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The cats mellow the sound quite a bit. I'm not sure if you're talking about cabin resonance (usually around 1,800 RPM) or the backfiring that the engine does from de-accelleration fuel cut off (DFCO). The first can be minimized by type and placement of the muffler and popping by the tuning. For starters the cats or installing resonators up front help.

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post #3 of 11 (permalink) Old 04-30-2012, 09:28 PM
 
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The resonance/vibration is caused by the exhaust system being "excited" at its harmonic frequency. To eliminate or reduce the annoying noise, you need to change the resonance frequency of your exhaust system. You need to make the system act like it is substantially longer than it is now. You have several options...

1. You can add "resonators" to the system. Installing a pair of 9" long or 12" long "straight-through" resonators will help. Choose resonators with a large inside diameter to minimize any negative effects on flow rate. A cheap pair of large-diameter "glass packs" will usually make a big improvement. You may need to experiment with the location to get the best results. Usually, these are best installed as far back in the system as possible. If you have mufflers at the rear, you will need to add the resonators further forward in the system.

2. If you have not re-installed the catalytic converters, you might never completely eliminate the noise but you should be able to reduce it significantly. Re-installing cats will make a huge improvement.

3. Adding a "J pipe" or similar feature to both sides of the exhaust system. These have become quite common on modified Camaro/G8 vehicles, as well as Porsche applications. The concept is to add a "dead-head" chamber to both sides of the system that will generate cancellation pulses at the objectionable frequency. Here's a quote from one of the Camaro forums that explains how to design the pipe:

"Originally Posted by BigRed585Lbs View Post
Simply put, the formula for determining the length of a Helmholtz chamber used to knock out a drone frequency is:

1100 feet/second (roughly the speed of sound) divided by the target frequency you're trying to eliminate (in cycles/second) gives a full wavelength in feet per cycle. Divide this number by 4 to get a quarter wavelength (a much more convenient length to work with). Finally, multiply this wavelength by 12 to get the chamber length in inches.

Tap this length of pipe into the exhaust tube, making sure the other end of the pipe is capped off, and you have a Helmholtz chamber that takes the annoying frequency and bounces it back into the flow 180 degrees out of phase, knocking it out. The results: no more drone."

Obviously, to use that formula you will need to know the frequency of the sound you are trying to eliminate.

Hope this helps.

You can also search for "eliminate drone" and you'll find a lot of ideas and solutions.
Good luck.

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1983 Pontiac Bonneville (G) wagon
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post #4 of 11 (permalink) Old 04-30-2012, 10:30 PM
 
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I had pacesetter LT's, no cats and magnaflow mufflers and it sounded like a monster.
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post #5 of 11 (permalink) Old 04-30-2012, 11:06 PM
 
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Pacesetters and no cats are loud, even with SLP LM2 mufflers you have a loud set up. Did you get your car tuned? When my car was on the dyno after a Maggie install it was loud not drone loud and tuning got rid of most cracking on deceleration. When I removed cats and installed Maggie volume and output changed dramatically from my previous shorties with cats and muffler delete system. I would try a dyno tune or add SLP resonators.
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post #6 of 11 (permalink) Old 05-02-2012, 12:34 PM Thread Starter
 
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I just youtubed GTO pacesetter and found many clips of other GTO's with different exhausts, but pacesetter headers. I found ALL of them have this drone. Am I correct in saying that I can get rid of the drone by following the formula given once I find the frequency of the drone? Seems to me I should have paid the extra for some different headers!
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post #7 of 11 (permalink) Old 05-02-2012, 05:34 PM
 
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Have some cats put back on. It sounds like it will help you.

Your other option is maybe different mufflers. My Corsa have zero drone.

2003 Corvette Z06 - MGW shifter, Corsa X pipe, Corsa Xtreme exhaust, Texas Speed long tubes w/o cats, PowerStop rotors/pads, Conti DWS tires, C6Z51 F&R sways, C5R headlights, tuned

04 GTO - sold
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post #8 of 11 (permalink) Old 05-03-2012, 11:04 AM Thread Starter
 
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Unfortunately, I have tried every combination. I am really thinking, since I saw many vehicles on youtube that have pacesetter headers, and they all have this drone, that the drone is a pacesetter problem... I spent a lot of money on them, and a lot of money having them put on. I am ready to throw them in the trash if I have to and if someone can give me the combination they have to get rid of the drone. I want noise, throat and deep tones!
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post #9 of 11 (permalink) Old 05-03-2012, 01:21 PM Thread Starter
 
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Quote:
Originally Posted by jpalamar View Post
Have some cats put back on. It sounds like it will help you.

Your other option is maybe different mufflers. My Corsa have zero drone.
Jpalamar, what do you have for exhaust from front to back? Do you have any sound clips on Youtube or anything? I am interested in what you have and how it sounds! I don't have anyone around me really that I can compare with, living in Coastal Maine...
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post #10 of 11 (permalink) Old 05-03-2012, 02:23 PM
 
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I had an 04 GTO. Stock exhaust manifods. JBA 05 catless mids . JBA 05 catback(comes with h-pipe). I loved it. Don't have any good sound clips but I'm sure you can Youtube them. It was a very deep old school sound.

My 03 Z06 has stock exhaust manifolds with cats, Corsa X pipe, and Corsa Extreme axle back. Much higher pitch and more exotic, maybe you could say modern, sound.

2003 Corvette Z06 - MGW shifter, Corsa X pipe, Corsa Xtreme exhaust, Texas Speed long tubes w/o cats, PowerStop rotors/pads, Conti DWS tires, C6Z51 F&R sways, C5R headlights, tuned

04 GTO - sold
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