Stock Exhaust

Boricua SS

Member
Nov 20, 2011
3,080
Ohio
jrSS said:
Aren those pics of the resonator? And not the muffler?

that looks too long to be the resonator Jeff... it looks like the length of my muffler... but we could be wrong...


Pittdawg said:
what am I missing?

the fact that you have an I6 :crackup:

Pittdawg said:
So the other OS has tons of posts about how aftermarket exhaust adds no horsepower only sound b/c the stock muffler is "straight through design". Here are to sets of pics of the stock muffler. Those pics don't exactly look straight through to me, what am I missing?

but seriously.. exhausts, even for us SS folks and 5.3L folks, are purely sound enhancers over performance.. unless were making stupid power and adding LT headers, does an exhaust factor into hp... the stock exhaust is very free flowing, even though youre seeing what youre seeing in those threads you provided...
 

Sparky

Member
Dec 4, 2011
12,927
jrSS said:
Aren those pics of the resonator? And not the muffler?

That monstrosity in those pics is the muffler for sure. Resonator is the small trash can hanging under the rear bumper.

I think part of the reason the muffler is pretty free-flowing despite having the grater holes and rat-maze pipes is because of its sheer size. Lots of room for exhaust to flow through it.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Sparky said:
That monstrosity in those pics is the muffler for sure. Resonator is the small trash can hanging under the rear bumper.

I think part of the reason the muffler is pretty free-flowing despite having the grater holes and rat-maze pipes is because of its sheer size. Lots of room for exhaust to flow through it.

I don't think size has anything to do with flow. My aftermarket resonator is 1/4 the size of the stock muffler but is entirely straight through. I feel comfortable estimating that my resonator flows much more than my stock muffler.

Any muffler pros out there who can opine as to the design of the inside of the stock muffler?
 

Sparky

Member
Dec 4, 2011
12,927
Pittdawg said:
I don't think size has anything to do with flow. My aftermarket resonator is 1/4 the size of the stock muffler but is entirely straight through. I feel comfortable estimating that my resonator flows much more than my stock muffler.

Any muffler pros out there who can opine as to the design of the inside of the stock muffler?

On an otherwise more restrictive design (perforated pipes and chambers), if you have a ton of space in the muffler for LARGE sections of perforated pipe then the restriction is reduced. A straight through design of course can have the same flow characteristics in a much smaller package.
 

million-miles

Member
Jan 10, 2012
189
Flow rate is flow rate. If the stock muffler flows as good as aftermarket then you will not notice any performance. Same with an intake. But i cant see the flow of a stock muffler having the same flow as aftermarket.

With that said if the exhaust is tuned to the vehicle better than aftermarket then it would be hard to notice any improvment on power.:thumbsup:
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
I'm interpreting the responses to mean yes the stock muffler has flow restricting baffles and chambers in it but the muffler itself is so large the restriction is minimized, at least to a certain extent. Further, the stock muffler was engineered for the exhaust system and a higher flowing muffler may not be properly balanced, i.e. could throw off the "scavenging effect". No one can confirm or deny that a higher flow muffler will yield any rwhp/tq. gain.

So I'm back to square one :hissyfit:
 

Sparky

Member
Dec 4, 2011
12,927
Pittdawg said:
I'm interpreting the responses to mean yes the stock muffler has flow restricting baffles and chambers in it but the muffler itself is so large the restriction is minimized, at least to a certain extent. Further, the stock muffler was engineered for the exhaust system and a higher flowing muffler may not be properly balanced, i.e. could throw off the "scavenging effect". No one can confirm or deny that a higher flow muffler will yield any rwhp/tq. gain.

So I'm back to square one :hissyfit:

Yeah pretty much.
 

limequat

Member
Dec 8, 2011
520
There's an article somewhere where the Chief Engineer, Ron Kociba, said that there was 30 hp tied up in the exhaust. It's hard to argue with the Chief.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
limequat said:
There's an article somewhere where the Chief Engineer, Ron Kociba, said that there was 30 hp tied up in the exhaust. It's hard to argue with the Chief.

Now you have piqued my interest! In that article, do you recall if they specified what they meant by "exhaust". For instance, the term "exhaust" could mean the exhaust side of the cylinder head, or beginning at the manifold, or the intermediate pipe, or the down pipe, or just the the cat back (which is probably most common layman's reference).
 

limequat

Member
Dec 8, 2011
520
Pittdawg said:
Now you have piqued my interest! In that article, do you recall if they specified what they meant by "exhaust". For instance, the term "exhaust" could mean the exhaust side of the cylinder head, or beginning at the manifold, or the intermediate pipe, or the down pipe, or just the the cat back (which is probably most common layman's reference).

This has been bothering me as well. Even with Mr. Kociba's say so I have a hard time believing that the muffler is that resrictive. Now if he meant "exhaust" as in "exhaust ports"...

Ok, here's the indirect quote:

"According to the engines designer, Ron Kociba, theres another 30 horsepower to be had just by adding dual exhausts."

http://www.iseecars.com/review/GMC/Envoy/2002


I bet this means splitting the exhaust manifold in two and running true duals all the way back. Makes sense, you have six runners jammed into one collector
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
I can't stand knowing how many chambers and baffles my stock muffler has. I'm installing a magnaflow. My Voy feels choked with my other mods, gotta open her up.
 

navigator

Member
Dec 3, 2011
504
I thought the theory was our platform has more than enough outflow (exhaust) to handle the inflow(intake) and to get more HP we needed performance on the intake side instead?
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
navigator said:
I thought the theory was our platform has more than enough outflow (exhaust) to handle the inflow(intake) and to get more HP we needed performance on the intake side instead?

1. Did you look at the pics I linked at the beginning of the thread? I don't care about theory I care about cold hard facts---open up the stock muffler and you see a rat's maze---this cannot be anything other than a distinct fl ow restriction.

2. I have a CAI with an oversized filter, a ported/polished tb and an extrude honed exhaust manifold, "theoretically", I should benefit from the increased flow of a straight through muffler.

Also, I have 4.10's and tuned pcm with no torque management so I am not overly concerned about losing low end torque as on my current combination of mods my low end torque is outstanding.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I think my aftermarket exhaust helped on the butt-dyno and a bit on the mpg which leads me to believe it flows a bit better.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
HARDTRAILZ said:
I think my aftermarket exhaust helped on the butt-dyno and a bit on the mpg which leads me to believe it flows a bit better.

What's your exact set up?
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Pittdawg said:
What's your exact set up?

Hooker aerochamber muffler w new pipe from local shop from cat back plus 18 inch 3.5 inch tip. Got bout 175 in it all.
 

steven76

Member
Mar 24, 2012
54
I have had my TB for one year and am on my 3rd muffler.

When I bought it, the previous owner had installed a Magnaflow and cut off the resonator. It was so loud, I couldn't stand the sound, so I had it changed to a different muffler. I don't recall the brand of the next muffler, but the muffler shop told me that it would be quieter with the same amount of flow. I still couldn't stand the sound of that one either

I finally changed that one out for a GM OEM muffler. I like the sound now; it sounds normal to me. But, the mpgs definitely suffered throughout the downgrade. I have not noticed any decrease in power though.

I am about to change it out one more time. Next payday, I am going to order a Walker Quiet-flow muffler and their resonator as well. I'm banking on the possibility that I might improve my mpgs again, and get my truck even quieter. I am all about having a stealth truck, not a loud one. My research and question-asking has informed me that a resonator is an integral part of keeping cars even quieter, and removing it can add as much as 25% more sound.
 

limequat

Member
Dec 8, 2011
520
steven76 said:
I have had my TB for one year and am on my 3rd muffler.

When I bought it, the previous owner had installed a Magnaflow and cut off the resonator. It was so loud, I couldn't stand the sound, so I had it changed to a different muffler. I don't recall the brand of the next muffler, but the muffler shop told me that it would be quieter with the same amount of flow. I still couldn't stand the sound of that one either

I finally changed that one out for a GM OEM muffler. I like the sound now; it sounds normal to me. But, the mpgs definitely suffered throughout the downgrade. I have not noticed any decrease in power though.

I am about to change it out one more time. Next payday, I am going to order a Walker Quiet-flow muffler and their resonator as well. I'm banking on the possibility that I might improve my mpgs again, and get my truck even quieter. I am all about having a stealth truck, not a loud one. My research and question-asking has informed me that a resonator is an integral part of keeping cars even quieter, and removing it can add as much as 25% more sound.

You're right on the money regarding the resonator. I first ran my 4.2 with your same setup. no resonator and magnaflow. Sounded good but way too damn loud. Put a resonator ahead of the magnaflow - no problem.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
steven76 said:
I have had my TB for one year and am on my 3rd muffler.

When I bought it, the previous owner had installed a Magnaflow and cut off the resonator. It was so loud, I couldn't stand the sound, so I had it changed to a different muffler. I don't recall the brand of the next muffler, but the muffler shop told me that it would be quieter with the same amount of flow. I still couldn't stand the sound of that one either

I finally changed that one out for a GM OEM muffler. I like the sound now; it sounds normal to me. But, the mpgs definitely suffered throughout the downgrade. I have not noticed any decrease in power though.

I am about to change it out one more time. Next payday, I am going to order a Walker Quiet-flow muffler and their resonator as well. I'm banking on the possibility that I might improve my mpgs again, and get my truck even quieter. I am all about having a stealth truck, not a loud one. My research and question-asking has informed me that a resonator is an integral part of keeping cars even quieter, and removing it can add as much as 25% more sound.

Lame muffler shop. They should have recommended the installation of a resonator instead of having you remove, buy and install multiple different mufflers. I hope you didn't have to pay for everything.
 

steven76

Member
Mar 24, 2012
54
Pittdawg said:
Lame muffler shop. They should have recommended the installation of a resonator instead of having you remove, buy and install multiple different mufflers.

Lame indeed. Joes Muffler Shop in Los Angeles. DONT EVER GO THERE!!

Pittdawg said:
I hope you didn't have to pay for everything.

:hissyfit: :lipsrsealed:
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
steven76 said:
I'm banking on the possibility that I might improve my mpgs again,

I can assure you that you will not recover the money you are about to spend on yet another exhaust by the minimal mpg gains possible. If you are ok with the sound, put your money into a tune or similar and get the mpg...unless you like paying for the muffler shop owner to take nice vacations.
 

steven76

Member
Mar 24, 2012
54
Pittdawg said:
So the other OS has tons of posts about how aftermarket exhaust adds no horsepower only sound

HARDTRAILZ said:
If you are ok with the sound

Revisiting the original post. Sound is the reason I keep dropping money on this. I am not pleased with the sound.

We all have different things that bug us about our GMTs. I desire a truck that isn't loud in appearance or sound.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
steven76 said:
I desire a truck that isn't loud in appearance or sound.

I drive an epic fail of a GMT to you I bet. I personally hate cookie cutter stockers. I did not even want a 360 due to the stock looks, but while they have grown on me, I love the loud n proud look of mine. But it takes all kinds. Best of luck in finding something that meets your approval.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
After all my research I have learned that the stock exhaust system consists of 3 inch piping from the cat to the OEM muffler inlet. Inside the OEM muffler the piping is reduced to 2.5 inches and then expands to 2.75 inch piping when it exits the OEM muffler and remains 2.75 inches all the way to the resonator. The resonator tip appeared smaller than 2.75 inches to me but I did not measure it before I trashed it.

So, after my research I have now ordered a 3 inch in 3 inch out 22" long Magnaflow straight through muffler and I will have it welded in place after it arrives in the mail.

My only concern now is that before I performed my research, I assumed the stock piping was 2.5 inches and therefore installed a 2.5 inch Vibrant Resonator in place of the stock resonator (purely for aesthetics). In hindsight it may have been better to buy a 3 inch resonator to avoid any restrictions greater than the OEM 2.75 inch pipes.

Oh well, they say you should always look for the silver lining, right? So, by mistake, I have designed a stepped/tapered exhaust system. In theory this could work, i.e. larger piping closer to the engine (3 inch)which is needed as the exhaust is hotter and needs the additional surface area to flow well while transitioning to smaller piping (3" to 2.75" to 2.5") farther from the engine provides better scavenging for the relatively cooler exhaust. I suspect the final 2.5 inch restriction may cause a loss of a couple horsepower in exchange for keeping the power band lower. I'll let you all know.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
Look at the crimped and bent pipe where it goes over the axle. I don't think you lose much, if any, power from that 2.5" resonator.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Boy was that shipping fast!
 

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Pittdawg

Original poster
Member
Dec 5, 2011
538
Just had it installed. Only drove around for approx. 15 min. from exhaust shop back to my place so a lot more driving is needed to give a full review. I can tell you that I absolutely love the sound :biggrin: My goal was to get the quietest most free flowing muffler available and I believe I met my goal although it is certainly louder than stock (I hope it doesn't gain too many db's after it "breaks in". The tone is (extremely) deep and mellow. I had a very slight drone after I swapped out the stock resonator (around 1800-2100 rpms) and I may have noticed some drone but at slightly higher rpms but I really don't have enough driving yet to draw any conclusions. I'll update later.
 

ItsOnVoy

Member
Nov 21, 2011
2,401
Got a video of how it sounds and maybe a link to were you got it from?
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
I'll take a "camera phone" video for ya all when I get a chance. I live in a very urban area and it is a bad idea to summon the local protection with loud stationary revving.

Here is a pic of having the muffler installed. Props to Ace Muffler in Westminister. They do good work for fair prices. Btw, I blame all of you for the mod bug and spending all my money. As I was standing there taking this picture, I was asking myself if I didn't need a fatter rear sway bar in place of that rather narrow looking stock bar :hissyfit:
 

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ItsOnVoy

Member
Nov 21, 2011
2,401
Pittdawg said:
Btw, I blame all of you for the mod bug and spending all my money.

20118387.jpg
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Rear sway bar doesnt do much. I pitched mine after trying none, front only, and rear only. The front makes the difference.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Spent the last hour trying to upload different sized camera phone videos to no avail so I finally started a youtube account.

08 Envoy with 4.2 Liter I6 and Mangaflow Muffler - YouTube

The first 40 seconds or so are with the windows up to give you an idea of in the cab sound. At about 40 seconds I roll the window down so you can hear the exhaust better. The phone's mic does a terrible job of transmitting the deeper tone but oh well still sounds pretty good for a shammy mic.
 

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