GM Performance Exhaust System
Thread Starter
Race Director
Joined: Aug 1999
Posts: 13,281
Likes: 2,509
From: Bluffton SC via Canton Oh
GM Performance Exhaust System
Just had my new GS a week and am wondering about the performance exhaust system. I know I can answer my own question this weekend when I am home from work in daylight but I'm too curious. No success in a forum search, sorry.
I think I know how the system works, the butterflies are open when starting the engine, and a nice growl. However the growl goes away in a couple of seconds, no problem there. But I'm thinking the butterflies never open back up. I was told by the dealer that above 1500 RPM they open? I've revved the engine somewhat, just 100 miles so being a little cautious, but certainly have ran the gears a little.
Franky if this is the best it gets I got hosed for $1,100!!!! Did not expect it to match my C5 with headers, high flow cats and Corsa Indys, but there is more roar from the engine bay then the rear of the car.
I know I can pull a fuse and leave the butterflies open but I was hoping to avoid that.
If there is something wrong here any idea what it could be? Always like to help the dealer out ya know!!!!
Thanks
I think I know how the system works, the butterflies are open when starting the engine, and a nice growl. However the growl goes away in a couple of seconds, no problem there. But I'm thinking the butterflies never open back up. I was told by the dealer that above 1500 RPM they open? I've revved the engine somewhat, just 100 miles so being a little cautious, but certainly have ran the gears a little.
Franky if this is the best it gets I got hosed for $1,100!!!! Did not expect it to match my C5 with headers, high flow cats and Corsa Indys, but there is more roar from the engine bay then the rear of the car.
I know I can pull a fuse and leave the butterflies open but I was hoping to avoid that.
If there is something wrong here any idea what it could be? Always like to help the dealer out ya know!!!!
Thanks
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,820
From: Charlotte, NC (formerly Endicott, NY)
Just had my new GS a week and am wondering about the performance exhaust system. I know I can answer my own question this weekend when I am home from work in daylight but I'm too curious. No success in a forum search, sorry.
I think I know how the system works, the butterflies are open when starting the engine, and a nice growl. However the growl goes away in a couple of seconds, no problem there. But I'm thinking the butterflies never open back up. I was told by the dealer that above 1500 RPM they open? I've revved the engine somewhat, just 100 miles so being a little cautious, but certainly have ran the gears a little.
Franky if this is the best it gets I got hosed for $1,100!!!! Did not expect it to match my C5 with headers, high flow cats and Corsa Indys, but there is more roar from the engine bay then the rear of the car.
I know I can pull a fuse and leave the butterflies open but I was hoping to avoid that.
If there is something wrong here any idea what it could be? Always like to help the dealer out ya know!!!!
Thanks
I think I know how the system works, the butterflies are open when starting the engine, and a nice growl. However the growl goes away in a couple of seconds, no problem there. But I'm thinking the butterflies never open back up. I was told by the dealer that above 1500 RPM they open? I've revved the engine somewhat, just 100 miles so being a little cautious, but certainly have ran the gears a little.
Franky if this is the best it gets I got hosed for $1,100!!!! Did not expect it to match my C5 with headers, high flow cats and Corsa Indys, but there is more roar from the engine bay then the rear of the car.
I know I can pull a fuse and leave the butterflies open but I was hoping to avoid that.
If there is something wrong here any idea what it could be? Always like to help the dealer out ya know!!!!
Thanks
Here is the description from the Service Manual:
Exhaust Tail Pipe Flow Control System Description and Operation
The Exhaust Flow Control (EFC) System enhances engine performance. The system has 2 modes of operation:
• Normal
• Competition
Normal Mode
When the vehicle is stationary with the engine running the exhaust flow control module (EFCM) commands the vacuum solenoid On, which supplies engine vacuum to both exhaust flow control valves. This causes the valves to close, diverting exhaust flow through a baffled path inside the mufflers. As vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3500 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open, diverting exhaust flow through an un-baffled path inside the mufflers, thus enhancing engine performance.
Competition Mode
When traction control is driver disabled, vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3000 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open; diverting exhaust flow through an un-baffled path inside the mufflers more frequently and at lower engine speeds.
The system also delays exhaust valve activity during wide-open throttle acceleration to inhibit exhaust valve actuation when the accelerator pedal is released and reapplied while shifting gears.
The EFCM has the ability to detect electrical malfunctions within the system. Any electrical malfunction detected will cause the system to be disabled and increased exhaust audibility.
The system uses the engine control module (ECM), body control module (BCM), electronic brake control module (EBCM), EFCM, exhaust flow control valve vacuum solenoid, vacuum reservoir, vacuum lines, 2 exhaust flow control valves and the serial data circuit to perform the system functions.
As you can see from the description winging the throttle in neutral probably isn't going to set all the conditions required to open the valves. They don't open until they are needed. When the throttle is wide open and the engine is over 3500 rpms the exhaust sounds pretty throaty to somebody standing by the road or where it is really awesome is on a track where the car is accelerating out of a turn in third. Being an instructor I have sat in the right seat of student's cars as they are being passed on the right and have heard that roar close up as Z06s and GSs pass us within a few feet.
Go some place where you can run wide open throttle at high engine speeds for 15 to 20 minutes and you will really enjoy the car and the noise it makes. Putt putting on the street or highway even at so called spirited driving levels doesn't cut it. Might as well be driving a Spark.
Bill
Team Owner
Joined: Sep 2000
Posts: 25,015
Likes: 2,709
From: Far NW 'burbs of Chicago
St. Jude Donor '13
We have the dual mode exhaust on our 2009, and love it.
Sure; you can get louder systems, or just pull the fuse on this one.
You can also get a headache and turn your wife into a raving maniac after a full day in the car.
We use the old fashioned Mild-to-Wild foot switch system so it can be easily opened at any time, I prefer that instead of the ones that use an extra fob or a dash button.
Sure; you can get louder systems, or just pull the fuse on this one.
You can also get a headache and turn your wife into a raving maniac after a full day in the car.
We use the old fashioned Mild-to-Wild foot switch system so it can be easily opened at any time, I prefer that instead of the ones that use an extra fob or a dash button.
Pro
Joined: Dec 2009
Posts: 729
Likes: 23
From: Scarsdale New York
Try driving a few times at WOT. At 3500 rpms and above the valves will open. See if that's enough sound for you. If not, purchase an aftermarket exhaust. I have Corsa Sport and really like it. No drone and screams at WOT. A little more exotic sounding. You don't need any switches by the way. Want more sound, just stomp on the gas.
Thread Starter
Race Director
Joined: Aug 1999
Posts: 13,281
Likes: 2,509
From: Bluffton SC via Canton Oh
Thanks for all the infomative information, especially your post Bill. There is nothing in the glove box manual nor the Chevy site to give any information. In fact what's the deal with the manual? Black and white cover and tissue paper pages??? They hurting that bad???
Bottom line and this is OK.....this was a spur of the moment purchase........ I did not do enough research, my fault or had I known there where so many complicated conditions vrs a Corsa I would have just bought another Corsa.
If I did a custom tune wonder if I could simplify these conditions?
But it is all good. After spending $13K on Mods on the C5 I have pledged to my wife not to mod this one because I am hoping to get a C7 in a few years if they don't butcher it.
I did buy a black license plate frame for $6 and she was OK with that and my insurance went down $75 a year so I got $69 on the plus side to mod up........
Bottom line and this is OK.....this was a spur of the moment purchase........ I did not do enough research, my fault or had I known there where so many complicated conditions vrs a Corsa I would have just bought another Corsa.
If I did a custom tune wonder if I could simplify these conditions?
But it is all good. After spending $13K on Mods on the C5 I have pledged to my wife not to mod this one because I am hoping to get a C7 in a few years if they don't butcher it.
I did buy a black license plate frame for $6 and she was OK with that and my insurance went down $75 a year so I got $69 on the plus side to mod up........
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 26
From: Austin Texas
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Drifting
Joined: Feb 2012
Posts: 1,256
Likes: 66
From: San Luis Obispo, California
Greg, an option to consider is the add-a-fuse method, inserted where the 10amp exhaust fuse is. Search CF, or my earliest posts. It costs @ $5 for the add-a-fuse, $3 for the on/off switch, & $2 for the insulated wire..all from the auto parts or hardware store.
Adding an on/off rocker switch for the exhaust valves enables you to leave them completely open, or close them at will. I mounted my on/off rocker switch in the upper fascia just behind the glove box where it's easy to reach, but I leave them open 99% of the time anyway.
Adding an on/off rocker switch for the exhaust valves enables you to leave them completely open, or close them at will. I mounted my on/off rocker switch in the upper fascia just behind the glove box where it's easy to reach, but I leave them open 99% of the time anyway.
Thanks for all the infomative information, especially your post Bill. There is nothing in the glove box manual nor the Chevy site to give any information. In fact what's the deal with the manual? Black and white cover and tissue paper pages??? They hurting that bad???
Bottom line and this is OK.....this was a spur of the moment purchase........ I did not do enough research, my fault or had I known there where so many complicated conditions vrs a Corsa I would have just bought another Corsa.
If I did a custom tune wonder if I could simplify these conditions?
But it is all good. After spending $13K on Mods on the C5 I have pledged to my wife not to mod this one because I am hoping to get a C7 in a few years if they don't butcher it.
I did buy a black license plate frame for $6 and she was OK with that and my insurance went down $75 a year so I got $69 on the plus side to mod up........
Bottom line and this is OK.....this was a spur of the moment purchase........ I did not do enough research, my fault or had I known there where so many complicated conditions vrs a Corsa I would have just bought another Corsa.
If I did a custom tune wonder if I could simplify these conditions?
But it is all good. After spending $13K on Mods on the C5 I have pledged to my wife not to mod this one because I am hoping to get a C7 in a few years if they don't butcher it.
I did buy a black license plate frame for $6 and she was OK with that and my insurance went down $75 a year so I got $69 on the plus side to mod up........
Drifting
Joined: Feb 2012
Posts: 1,256
Likes: 66
From: San Luis Obispo, California
Hey Bud, I've listened to that video a few times & many thanks for posting it.
With the valves open, how much of an increase in sound did you really notice with the LS7 system into your NPPs? Was it significant, very noticeable, fairly minor...or??
It actually sounds like it back-breathes between shifts a lot more, & pops a bit more on decel, than the stock LS3-Npp system does. Lastly, did the sound change very much , or at all, after the tune? I don't care about valves closed, but the sound change with them open.
With the valves open, how much of an increase in sound did you really notice with the LS7 system into your NPPs? Was it significant, very noticeable, fairly minor...or??
It actually sounds like it back-breathes between shifts a lot more, & pops a bit more on decel, than the stock LS3-Npp system does. Lastly, did the sound change very much , or at all, after the tune? I don't care about valves closed, but the sound change with them open.
Melting Slicks
Joined: Dec 2006
Posts: 2,694
Likes: 106
I did the switch mode, not because was the cheapest one (less than $20), but because it was the best option for me. Bought the switch at Radio Shack. There're many different ones, but I chose a slim one with a light, to signify the quiet position... but didn't connect the light. It's invisible, but easily reached. Installation is a snap, and you don't need to tap into anything other than the NPP fuse (pics below). Good luck.
Team Owner
Joined: Jun 2005
Posts: 46,295
Likes: 2,596
From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
While you are technically in the correct forum, generally speaking the issues/instruction/add-ons/operation of things like NPP are in C6 Gen. All you have to do is hit advanced search in the red band and enter key words, like NPP.
I like all the alternatives listed above, but the one I like the most on my '08 is possibly less expensive than some. The collars offered by some vendors for the NPP exhaust that keeps the "flaps/valves" slightly open. The amount of slightly open depends on what you like, and what you can stand at highway speed.
It is not cockpit-controllable other than to physically get out, get under the car and readjust it. But once set, it is great and it's about $25. My car now always has a slight rumble at idle and all thru the rpm range, while still having the wide-open-throttle, NPP, loudness.
I like all the alternatives listed above, but the one I like the most on my '08 is possibly less expensive than some. The collars offered by some vendors for the NPP exhaust that keeps the "flaps/valves" slightly open. The amount of slightly open depends on what you like, and what you can stand at highway speed.
It is not cockpit-controllable other than to physically get out, get under the car and readjust it. But once set, it is great and it's about $25. My car now always has a slight rumble at idle and all thru the rpm range, while still having the wide-open-throttle, NPP, loudness.
Thread Starter
Race Director
Joined: Aug 1999
Posts: 13,281
Likes: 2,509
From: Bluffton SC via Canton Oh
My this forum is awesome!!!! Ask a simple ? and great many great answers!!!! We should run the stinkin government like this.....
I like the switch option. I've not hammered it yet but based on what I hear on start up I'm thinking the constant droan would get old. Thanks again!!!
I give.....what does NPP stand for???? Never heard the term thus challenged to do a search with it. New C6 10 days ago..........
I like the switch option. I've not hammered it yet but based on what I hear on start up I'm thinking the constant droan would get old. Thanks again!!!
I give.....what does NPP stand for???? Never heard the term thus challenged to do a search with it. New C6 10 days ago..........
Last edited by Greg00Coupe; Nov 28, 2012 at 08:39 PM.
Team Owner
Joined: Jun 2005
Posts: 46,295
Likes: 2,596
From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
all options on C6s have codes. the performance exhaust that is a regular production option (RPO) is labeled "NPP." to my knowledege, it is a made up acronym with no words behind it.
Melting Slicks
Joined: Nov 2003
Posts: 2,155
Likes: 56
From: Escondido CA
Melting Slicks
Joined: Nov 2003
Posts: 2,155
Likes: 56
From: Escondido CA
Hey Bud, I've listened to that video a few times & many thanks for posting it.
With the valves open, how much of an increase in sound did you really notice with the LS7 system into your NPPs? Was it significant, very noticeable, fairly minor...or??
It actually sounds like it back-breathes between shifts a lot more, & pops a bit more on decel, than the stock LS3-Npp system does. Lastly, did the sound change very much , or at all, after the tune? I don't care about valves closed, but the sound change with them open.
With the valves open, how much of an increase in sound did you really notice with the LS7 system into your NPPs? Was it significant, very noticeable, fairly minor...or??
It actually sounds like it back-breathes between shifts a lot more, & pops a bit more on decel, than the stock LS3-Npp system does. Lastly, did the sound change very much , or at all, after the tune? I don't care about valves closed, but the sound change with them open.
Pro
Joined: Dec 2009
Posts: 729
Likes: 23
From: Scarsdale New York
Great looking C6R you have then. Very sharp and great color combos!