Exhaust Drone

Discussion on fuel delivery & intake/exhaust tech & mods.
ImpalaPPV
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Re: Exhaust Drone

Post by ImpalaPPV »

What exactly is a J-pipe?
Pursuit
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Re: Exhaust Drone

Post by Pursuit »

It is installed internally within a muffler from the factory. If you were to peel the skin off of your factory muffler you would see a short section of pipe that is teed off of the pipe routed though the muffler, it is shapped like a J and is capped off.
There are several pics out there where people have documented this. Some people have just welded a "J -pipe" to their existing system.

Maurice
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2011 Caprice Phantom Black 9C3
2012 Impala 9C1
1995 9C1 Caprice
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GTObert
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Re: Exhaust Drone

Post by GTObert »

After doing some research and speaking with the sound engineer at my work, I have determined that the pipe need not even be in a J shape. In fact, a straight pipe will probably work better. The idea is to add a pipe to your exhaust and cap that pipe off. If the pipe length is correct the sound waves will bounce off the capped end and return into your exhaust, cancelling the incoming sound waves.
2011 9C1
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GXPaycheck
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Re: Exhaust Drone

Post by GXPaycheck »

J pipes can be added to any exhaust.
The best thread is in the Grrrr8.net forum, but it's down at the moment. I will post the link when it comes back up.
One thing to note, J pipes will not get rid of the AFM changeover drone. Only the exhaust drone.
Navy Lifer
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Re: Exhaust Drone

Post by Navy Lifer »

It's interesting that the OE PPV mufflers do a very good job of canceling out drone--so I'm not sure what is different about AFM "changeover" or exhaust drone. Using the SS sedan mufflers on my car now creates a distinct difference in exhaust tone as the AFM transitions back forth--more than a bit annoying, too. Remember, these mufflers are made to work with the non-AFM LS3.

The J-pipe is, simply, a Helmholtz resonator.

http://en.wikipedia.org/wiki/Helmholtz_resonance" onclick="window.open(this.href);return false;

"The theory of Helmholtz resonators is used in motorcycle and car exhausts to alter the sound of the exhaust note and for differences in power delivery by adding chambers to the exhaust. Exhaust resonators are also used to reduce potentially loud and obnoxious engine noise where the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust."

There are Helmholtz resonator(s) used in the PPV, G8, and SS intake system--everyone looks at the odd-shaped plastic ducting and deems it restrictive, but most especially it's considered ugly in appearance. Reality is that it probably flows pretty well.

Same was true on the 94-96 B-body--from the air filter housing to the throttle body was a series of resonant chambers, all intended to cancel out intake noise/roar (just what an enthusiast LIKES....so it's gotta go). In fact, it has been suggested that the "home plate" that sits on top of the of the LT1 intake manifold actually smooths the flow of intake air in front of the throttle body, and acts as sort of a "shock absorber" for the air mass as the throttle is slammed shut or pushed wide open, which is not what the performance enthusiast owners want to acknowledge--and I don't know if any data exists to prove or disprove this, but it makes sense to me.
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GTObert
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Re: Exhaust Drone

Post by GTObert »

As I understand it, a 1/4 wave resonance tube is not the same as a Helmholtz resonator. The former describes the J pipes that are being discussed and the latter describes expansion chamber type mufflers. I flipped through a very technical book supplied by the sound engineer at my work and this is explained, albeit in a way that I barely grasp. The math (which I also will not pretend to understand) used to design each is very different.

The sound engineer and I have made plans to sample the resonance in my cabin and design a resonance tube that will totally eliminate the noise. I'll let you know how it works.

Also, AFM drone keeps being brought up. I noticed this right away when I bought the car and it's the first thing I changed when I got HP Tuners. I don't have any plans to reactivate it.
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Tom Slick
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Re: Exhaust Drone

Post by Tom Slick »

Anyone tried the delta-flow Flowmasters on their Caprice? They are designed to resonate less than the standard versions, so they are quieter in the cabin.

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1932 Glassic Ford Model A Roadster Replica - Ford 302/C4, approx. 1400lb... :-)
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Navy Lifer
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Re: Exhaust Drone

Post by Navy Lifer »

GTObert wrote:As I understand it, a 1/4 wave resonance tube is not the same as a Helmholtz resonator. The former describes the J pipes that are being discussed and the latter describes expansion chamber type mufflers. I flipped through a very technical book supplied by the sound engineer at my work and this is explained, albeit in a way that I barely grasp. The math (which I also will not pretend to understand) used to design each is very different.
I'll agree with this--the resonant behavior of a system that handles a number of dynamic influences, as an automotive exhaust system is a combination of problems & solutions. The Helmholtz concept is probably best called a specific development of the basic 1/4 wave resonance approach, so it CAN be employed in exhaust--whether it is in the case of PPV or aftermarket solutions applicable to many vehicles, including PPV, I don't know specifically. The Solo exhaust would appear to be an adjustable 1/4 wave tuning device, for example. The real challenge is that AFM adds another dimension to the problem.

There's tons of info out there--some is, as you say, a bit on the "DEEP end of the pool" to be easily understood by the layman, sort of like old math vs common core. I know the answer to 38 x 17 (just a random pair I chose), pretty much off the top of my head, but today the process of HOW the student arrived at the answer is the thing being forced into the mix--same goes for the math with the sound attenuation formulas--no idea which came first....did someone try something and get a desired result "by accident" and then the data was developed to explain what they did, or did it get worked out on paper (mathematically) first and THEN proven with a working model? Doesn't matter--today we know there are a number of things available to allow us to understand, explain, and "fix" problems such as exhaust system resonance - aka drone.

Here's a couple of web pages (of many to choose from) with some further food for thought:

https://www.physicsforums.com/threads/a ... cs.475510/" onclick="window.open(this.href);return false;

http://www.acoustics.asn.au/conference_ ... ers/34.pdf" onclick="window.open(this.href);return false;

Vehicle manufacturers will employ a number of things to mitigate the amount of sound (noise) in the final product. Sometimes it is to meet a specific set of requirements, sometimes it is to enhance a certain characteristic in the sound produced, but it is almost always based on economic limitations, at least for mass-produced components, especially automobiles. This is easily demonstrated by the difference in a PPV with L77 and SS sedan with LS3--the target customer is very different in each case, and throw in on top of that the difference in characteristics of the two engines, and the effect of AFM on the exhaust pulse "tuning" challenge with the PPV.

For the time being, with AFM still active, the SS sedan mufflers on my PPV would not be allowed to leave the factory, as the exhaust tone and resonance in AFM mode is not at all pleasant inside the passenger compartment. Without cutting open the mufflers to compare them, I do understand why I have a problem, and I know there are several solutions....none of which are "perfect".

1. use stock mufflers - too "quiet"?
2. deactivate AFM - impact on fuel economy?
3. aftermarket solutions - Solo adjustable resonance pipe(s) - works with AFM?
4. your idea(s) here
GXPaycheck
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Re: Exhaust Drone

Post by GXPaycheck »

Here's the link to the G8 forum thread (and its s big one!) on j-pipes:
http://forum.grrrr8.net/showthread.php?t=10801" onclick="window.open(this.href);return false;
ImpalaPPV
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Re: Exhaust Drone

Post by ImpalaPPV »

I don't think I ever realized exhaust could be quite so complicated...

Would I be correct in saying that technically these cars (Caprice) really need to have two different exhaust systems because essentially with AFM activated we have two engines with different sounds characteristics? Clearly, two exhaust systems on the same car is not an option; but what are our options?

So far I've seen you guys talking about:

J-Pipes - Works on V8 drone when tuned -doesn't help AFM drone -what about 2 sets of j-pipes?
Corsa Exhaust - I don't think anybody has this installed... What about l-99 Camaro guys?
Solo Exhaust - Some of you guys run this set up in some form. How's the drone / noise?
Chevy SS Mufflers - Drone with AFM
Flowmasters - In my experience, drone 24-7 in any car. Anyone running them?

Has anyone considered:

Dynomax V-T mufflers? I've heard mixed reviews but they appear to to reduce drone. Will they work with AFM? Will they last? Are they a gimmick? Who knows...There is a G8 on YouTube that runs them.

What about resonators?

I really can't say that I know what they do but the stock system has a whole bunch of them in it. What about running performance mufflers, resonators and j- pipes?

I know I probably missed the post where all of this was discussed and explained if I did I apologize.
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