Dual Mode Exhaust
Le Mans Master
Joined: Oct 2014
Posts: 9,731
Likes: 42
I did the QTP Cutouts. Love the sound and the ability to be quiet as a church mouse.
Melting Slicks
Joined: Mar 2011
Posts: 2,708
Likes: 83
From: Arkansas
Factory NPP mufflers are OPEN by default. Vacuum closes the valves above idle to 3500rpms by an electronic signal. OP can simply bolt them on and they will be OPEN all the time until he decides to install vacuum and a controller. Most guys that have the factory option simply pull the fuse and they stay open all the time.
Melting Slicks
Joined: Aug 2006
Posts: 2,409
Likes: 129
From: Fairview Heights IL
I just had NPPs added to my '07 vert to allow more hp than the stock exhaust would permit with the Edelbrock s/c. The really great part is the special Sunset Orange controller. I can select quiet, above a user-set rpm, and full open (loud!) at the touch of a button. Sadly my controller, which is integrated into the DIC display, is no longer for sale and the web site is off-line.
Race Director
Joined: Dec 2013
Posts: 12,502
Likes: 3,631
Hence the pneumatic vavle does not close until the motor gets to 3k with a specific gas pedal press to allow the gates to snap open to put the car into loud mode.
NPP muffler, and the left and right tubes are the quiet tips piping, and the cross pipe is the tip that has the NPP valve on it, a direct through muffler route isntead when the NPP gate is open (holes in the pipe just make it a glass pack design instead).
Instructor
Joined: Sep 2013
Posts: 104
Likes: 17
From: San Antonio Texas
Life made easy,and either just bypass the pneumatic valve so the gates open when you get into the gas pedal deep to begin with, or just pull the fuse so the gates stay open instead.
Hence the pneumatic vavle does not close until the motor gets to 3k with a specific gas pedal press to allow the gates to snap open to put the car into loud mode.
NPP muffler, and the left and right tubes are the quiet tips piping, and the cross pipe is the tip that has the NPP valve on it, a direct through muffler route isntead when the NPP gate is open (holes in the pipe just make it a glass pack design instead).
Hence the pneumatic vavle does not close until the motor gets to 3k with a specific gas pedal press to allow the gates to snap open to put the car into loud mode.
NPP muffler, and the left and right tubes are the quiet tips piping, and the cross pipe is the tip that has the NPP valve on it, a direct through muffler route isntead when the NPP gate is open (holes in the pipe just make it a glass pack design instead).
There are tooooons of ways to control this exhaust. I used a vacuum pump
https://www.corvetteforum.com/forums...ne-intake.html
Most people use engine vacuum (like was done on the factory option, but a switch is used aftermarket) or just pull the fuse or add a switch to the fuse if factory equipped. However, if factory equipped, you can't make it quiet full time (valves closed through the whole RPM range) without modifying the system.
1st Gear
Joined: Jun 2016
Posts: 1
Likes: 0
From: San Antonio TX
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Advanced
Joined: Jul 2016
Posts: 86
Likes: 4
From: Utah
Just signed up to the forums (just got my first Corvette 2 weeks ago) so I don't think I can PM? But I'll buy your exhaust assuming its not damaged (but doesnt sound like it is).
Heel & Toe
Joined: Jul 2016
Posts: 16
Likes: 0
Factory NPP mufflers are OPEN by default. Vacuum closes the valves above idle to 3500rpms by an electronic signal. OP can simply bolt them on and they will be OPEN all the time until he decides to install vacuum and a controller. Most guys that have the factory option simply pull the fuse and they stay open all the time.
