Stock muffler mod
Thread Starter
St. Jude Partner since 89
Joined: Oct 2005
Posts: 774
Likes: 4
From: Lebanon, TN
St. Jude Donor '09
Stock muffler mod
Has anyone opened up the C7Z stock muffler (cans) and blocked off the internal pipe holes and removed the packing like some of us did on the C6Z?
Tech Contributor
Joined: Jan 2006
Posts: 4,761
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From: Saint Louis MO
St. Jude Donor '14-'15
I have scoped the NPP exhaust for the C7, and there is no packing - simply perf holes for re-route and resonation chambers.
I'd cut one of these extra ones open, but someone can put it to good use since it's still new. Once we have someone wind up with a wrecked one, we can have the full inside pics rather than just endoscope pics.
I'm happy to post those if you'd like.
I'd cut one of these extra ones open, but someone can put it to good use since it's still new. Once we have someone wind up with a wrecked one, we can have the full inside pics rather than just endoscope pics.
I'm happy to post those if you'd like.
Tech Contributor
Joined: Jan 2006
Posts: 4,761
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From: Saint Louis MO
St. Jude Donor '14-'15
The perf holes run the entire length of the inner pipe. By blocking those, you eliminate that pipe entirely.
So, it wouldn't really be 4 outlets at all unless you cut the inner pipe, which changes the length and resonant frequency inside the muffler. Might be great, might be horrible.
So, it wouldn't really be 4 outlets at all unless you cut the inner pipe, which changes the length and resonant frequency inside the muffler. Might be great, might be horrible.
Tech Contributor
Joined: Jan 2006
Posts: 4,761
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From: Saint Louis MO
St. Jude Donor '14-'15
I think visuals would help here...
If you blocked the perf holes, there is no more bi-modal exhaust. You'd have a straight pipe with an actuator, which when closed will act as a proverbial potato in the tailpipe.
No matter which pipe's holes you block, you still cause this situation. The larger holes on the main pipe allow the flow/waves to travel into the can/shell and bypass to the secondary tube. That secondary tube has smaller holes to attenuate the sound and alter the flow of the exhaust gases.
Block the large one, and you have the situation described above - a straight pipe with an actuator. Block the small one, and you have a pipe with a resonation chamber and an actuator.
Both end in disaster.
If you blocked the perf holes, there is no more bi-modal exhaust. You'd have a straight pipe with an actuator, which when closed will act as a proverbial potato in the tailpipe.
No matter which pipe's holes you block, you still cause this situation. The larger holes on the main pipe allow the flow/waves to travel into the can/shell and bypass to the secondary tube. That secondary tube has smaller holes to attenuate the sound and alter the flow of the exhaust gases.
Block the large one, and you have the situation described above - a straight pipe with an actuator. Block the small one, and you have a pipe with a resonation chamber and an actuator.
Both end in disaster.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
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From: CA.
St. Jude Donor '13-'14-'15
Either buy a catback system that has both sides open all the time OR so like many of have done---simply eliminate both mufflers and intall the dual 4" flowmaster dual wall tips--Just barely louder that NPP exhaust with the one side open---no resonance-- no drone and all can be done for about $150--Sounds awesome at WOT around town mello
This car with 4 cats is actually quite tame without mufflers at all--at P/T
PLUS you save off over 50lbs of weight off the rear
Thread Starter
St. Jude Partner since 89
Joined: Oct 2005
Posts: 774
Likes: 4
From: Lebanon, TN
St. Jude Donor '09
[QUOTE=Theta;1589669703]I think visuals would help here...
QUOTE]
Yeah it probably would because you have no idea what I am asking about. I had some from my C6Z but probably could not produce them. This is not about defeating the NPP. On the C6Z - inside the muffler can, the straight through pipe is perforated and the can is packed with some kind of fiberglass sound deadening material, the mod was to remove the material and close off the perforations so basically it was a straight through pipe. I think someone has already posted that there is no packing material in the C7 cans. Hope this helps.
QUOTE]
Yeah it probably would because you have no idea what I am asking about. I had some from my C6Z but probably could not produce them. This is not about defeating the NPP. On the C6Z - inside the muffler can, the straight through pipe is perforated and the can is packed with some kind of fiberglass sound deadening material, the mod was to remove the material and close off the perforations so basically it was a straight through pipe. I think someone has already posted that there is no packing material in the C7 cans. Hope this helps.
Last edited by Nithros; May 24, 2015 at 09:10 AM.
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Thread Starter
St. Jude Partner since 89
Joined: Oct 2005
Posts: 774
Likes: 4
From: Lebanon, TN
St. Jude Donor '09
I think that route is a waste of time with minimal positive results--
Either buy a catback system that has both sides open all the time OR so like many of have done---simply eliminate both mufflers and intall the dual 4" flowmaster dual wall tips--Just barely louder that NPP exhaust with the one side open---no resonance-- no drone and all can be done for about $150--Sounds awesome at WOT around town mello
This car with 4 cats is actually quite tame without mufflers at all--at P/T
PLUS you save off over 50lbs of weight off the rear
Either buy a catback system that has both sides open all the time OR so like many of have done---simply eliminate both mufflers and intall the dual 4" flowmaster dual wall tips--Just barely louder that NPP exhaust with the one side open---no resonance-- no drone and all can be done for about $150--Sounds awesome at WOT around town mello
This car with 4 cats is actually quite tame without mufflers at all--at P/T
PLUS you save off over 50lbs of weight off the rear
Last edited by Nithros; May 24, 2015 at 08:38 AM.
Pro
Joined: Jan 2010
Posts: 629
Likes: 65
From: Freedom PA
Here's a link to the C6 muffler mod the OP was talking about.
On the C6 NPP mufflers there was a resonance chamber at each end. It didn't require the exhaust to flow through the perforations to get to the other outlet. However by closing off the perforations the NPP side became a true straight pipe without any turbulence. The result was a louder exhaust note with the NPP valves open. When the valves were closed you had normal quiet exhaust sound. It was/is a very popular mod for C6 NPP cars to make them a little louder for 0 dollars, and a lot of effort.
The pictures in the thread don't show the resonance chamber because you opened the can only where the perforated pipe was.
I hope this clears up the misunderstanding as I do believe the C7 muffler has similar resonance chambers. I have never seen a muffler that required full exhaust flow through the perforated pipe. They are mainly used to absorb pressure pulses.
https://www.corvetteforum.com/forums...eo-inside.html
Ed
On the C6 NPP mufflers there was a resonance chamber at each end. It didn't require the exhaust to flow through the perforations to get to the other outlet. However by closing off the perforations the NPP side became a true straight pipe without any turbulence. The result was a louder exhaust note with the NPP valves open. When the valves were closed you had normal quiet exhaust sound. It was/is a very popular mod for C6 NPP cars to make them a little louder for 0 dollars, and a lot of effort.
The pictures in the thread don't show the resonance chamber because you opened the can only where the perforated pipe was.
I hope this clears up the misunderstanding as I do believe the C7 muffler has similar resonance chambers. I have never seen a muffler that required full exhaust flow through the perforated pipe. They are mainly used to absorb pressure pulses.
https://www.corvetteforum.com/forums...eo-inside.html
Ed
Last edited by Old Yellow; Jun 2, 2015 at 11:58 PM. Reason: spell checker
Tech Contributor
Joined: Jan 2006
Posts: 4,761
Likes: 240
From: Saint Louis MO
St. Jude Donor '14-'15
I was banging my head against the keyboard for half an hour before writing that reply wondering what in the heck I was missing here.
This is nearly the opposite end of the spectrum from what I thought the OP was suggesting. I have to admit that I have precious little C6 insight, so that's my fault for assuming.
I actually came out here with a borescope and made a decently-long video that I was getting ready to upload to show why what I was saying was correct, but we were, indeed, talking about two different things. My bad, Nithros!
My thoughts were simply on flow, not resonance. Makes a hell of a lot more sense - otherwise, as I had argued, you'd have a proverbial veggie in the tailpipe!
Hell, if it wasn't going to help someone down the road when it gets sold, I would have cut open a C7 muffler right here to show it off.
Edit: From simple measurements, it would appear that the chambers would have to be significantly smaller on the C7 mufflers based solely on the start/stop of the perfs, and the end of the secondary res tube. It's funny that in 18 months, none of us has cut one open.
Last edited by Theta; Jun 3, 2015 at 12:13 AM.
Melting Slicks
Joined: Dec 1999
Posts: 2,041
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From: Tulsa, Ok
I'm still searching and here's my original thread on the subject
https://www.corvetteforum.com/forums...-cut-away.html
https://www.corvetteforum.com/forums...-cut-away.html
Tech Contributor
Joined: Jan 2006
Posts: 4,761
Likes: 240
From: Saint Louis MO
St. Jude Donor '14-'15
I'm still searching and here's my original thread on the subject
https://www.corvetteforum.com/forums...-cut-away.html
https://www.corvetteforum.com/forums...-cut-away.html
Herein lied the problem with my argument - he was talking about a C6 NPP muffler, and I was focused on (what we think to be a correct representation of) a C7 NPP muffler.
After about 3 minutes of looking at the C6 muffler, the benefits of the mod became clear (if not a bit difficult for DIY sans-welder).
Tech Contributor
Joined: Oct 1999
Posts: 41,037
Likes: 9,799
From: Charlotte, NC (formerly Endicott, NY)
Here's a link to the C6 muffler mod the OP was talking about.
On the C6 NPP mufflers there was a resonance chamber at each end. It didn't require the exhaust to flow through the perforations to get to the other outlet. However by closing off the perforations the NPP side became a true straight pipe without any turbulence. The result was a louder exhaust note with the NPP valves open. When the valves were closed you had normal quiet exhaust sound. It was/is a very popular mod for C6 NPP cars to make them a little louder for 0 dollars, and a lot of effort.
The pictures in the thread don't show the resonance chamber because you opened the can only where the perforated pipe was.
I hope this clears up the misunderstanding as I do believe the C7 muffler has similar resonance chambers. I have never seen a muffler that required full exhaust flow through the perforated pipe. They are mainly used to absorb pressure pulses.
https://www.corvetteforum.com/forums...eo-inside.html
Ed
On the C6 NPP mufflers there was a resonance chamber at each end. It didn't require the exhaust to flow through the perforations to get to the other outlet. However by closing off the perforations the NPP side became a true straight pipe without any turbulence. The result was a louder exhaust note with the NPP valves open. When the valves were closed you had normal quiet exhaust sound. It was/is a very popular mod for C6 NPP cars to make them a little louder for 0 dollars, and a lot of effort.
The pictures in the thread don't show the resonance chamber because you opened the can only where the perforated pipe was.
I hope this clears up the misunderstanding as I do believe the C7 muffler has similar resonance chambers. I have never seen a muffler that required full exhaust flow through the perforated pipe. They are mainly used to absorb pressure pulses.
https://www.corvetteforum.com/forums...eo-inside.html
Ed
Bill
Melting Slicks
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Safety Car
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So I do that and can find both the c6z muffler cut out threads npp stuff which I have done to 2 other cars. And also a long thread in the c6 stock muffler.
If you see a thread for the inside of a c7 muffer could you please post a link to it? I am not finding one at all
If you see a thread for the inside of a c7 muffer could you please post a link to it? I am not finding one at all
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