Npp
Thread Starter
Racer
Joined: Jun 2020
Posts: 274
Likes: 43
From: Vestavia Hills, AL
Npp
Hello everyone,
I just purchased a 2009 C6 (coming from a C4). I know the RPO code sheet says I have NPP exhaust which I have been reading about people pulling the fuse making it more aggressive all the time. Mine is loud all the time which I don't mind. I checked the fuse box to see if someone pulled the fuse but it is still there. Any thoughts as to why it is always loud if the fuse is in? Thanks
I just purchased a 2009 C6 (coming from a C4). I know the RPO code sheet says I have NPP exhaust which I have been reading about people pulling the fuse making it more aggressive all the time. Mine is loud all the time which I don't mind. I checked the fuse box to see if someone pulled the fuse but it is still there. Any thoughts as to why it is always loud if the fuse is in? Thanks
Safety Car
Joined: Sep 2013
Posts: 4,355
Likes: 2,633
From: Draper Utah
So I assume you have checked for an NPP switch being added when you checked the fuse? If not that's the first thing to check. Also check the OBD2 port under the dash to make sure nothing is plugged in as a company called Dashlogic makes a product that plugs in and controls the NPP.
I also assumed that you checked the NPP fuse was good?
Have you actually looked in the tailpipe and checked that your actuators are not closing? That's the next step.
If the actuators are not closing the next item is to check vacuum at the actuators as they have been known to fail.
Answer those and we can go from there.
I also assumed that you checked the NPP fuse was good?
Have you actually looked in the tailpipe and checked that your actuators are not closing? That's the next step.
If the actuators are not closing the next item is to check vacuum at the actuators as they have been known to fail.
Answer those and we can go from there.
Thread Starter
Racer
Joined: Jun 2020
Posts: 274
Likes: 43
From: Vestavia Hills, AL
So I assume you have checked for an NPP switch being added when you checked the fuse? If not that's the first thing to check. Also check the OBD2 port under the dash to make sure nothing is plugged in as a company called Dashlogic makes a product that plugs in and controls the NPP.
I also assumed that you checked the NPP fuse was good?
Have you actually looked in the tailpipe and checked that your actuators are not closing? That's the next step.
If the actuators are not closing the next item is to check vacuum at the actuators as they have been known to fail.
Answer those and we can go from there.
I also assumed that you checked the NPP fuse was good?
Have you actually looked in the tailpipe and checked that your actuators are not closing? That's the next step.
If the actuators are not closing the next item is to check vacuum at the actuators as they have been known to fail.
Answer those and we can go from there.
Last edited by wood78221; Nov 16, 2020 at 01:18 PM.
Instructor
Joined: Jan 2020
Posts: 122
Likes: 39
From: Massachusetts
Safety Car
Joined: Sep 2013
Posts: 4,355
Likes: 2,633
From: Draper Utah
The NPP exhaust has an actuator mounted above each tailpipe as in the picture below. They are easy to see if you look at the car from the rear.
Thread Starter
Racer
Joined: Jun 2020
Posts: 274
Likes: 43
From: Vestavia Hills, AL
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Thread Starter
Racer
Joined: Jun 2020
Posts: 274
Likes: 43
From: Vestavia Hills, AL
Thread Starter
Racer
Joined: Jun 2020
Posts: 274
Likes: 43
From: Vestavia Hills, AL
Pro
Joined: Jul 2020
Posts: 509
Likes: 180
Safety Car
Joined: Sep 2013
Posts: 4,355
Likes: 2,633
From: Draper Utah
FWIW - There is a popular modification to the base mufflers where you cut them open, modify the guts and weld them back together. You can Google it if you want more info. It appears these mufflers have a similar modification.
Burning Brakes
Joined: Dec 2011
Posts: 876
Likes: 116
From: HOMESTEAD FL
The NPP system in my car was removed when I changed the rear diffuser to a center exit design. After about 5-6 years of a glass pack muffler system, I decided to build my own NPP exhaust. I purchased 2x vacuum valves, 3x mufflers, a box of straight 3" stainless steel pipe a TIG welder and made my own system. My set up could have been done with just 2x mufflers however I wanted the quiet side to be quieter so I added a center muffler that would drop the sound more when the NPP was closed.
Perhaps this could give you some ideas...
https://www.corvetteforum.com/forums...e-bi-mode.html
SPEED SAFE, NICK
Perhaps this could give you some ideas...
https://www.corvetteforum.com/forums...e-bi-mode.html
SPEED SAFE, NICK