NPP disabled
Thread Starter
Safety Car
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From: Chester VA
NPP disabled
I know that the NPP can be disabled to allow free-flow exhaust with less restriction by using the menus on the screens, or by pulling fuse #42 (on a 2015 anyway).
Do those two techniques result in exactly the same result? I'm sure that pulling the fuse freezes the muffler valves open 100% of the time. If I set the menus to provide less restriction, does that also keep the valves open 100% of the time, or are there situations when the valves might need to close a bit?
TIA,
Larry
Do those two techniques result in exactly the same result? I'm sure that pulling the fuse freezes the muffler valves open 100% of the time. If I set the menus to provide less restriction, does that also keep the valves open 100% of the time, or are there situations when the valves might need to close a bit?
TIA,
Larry
Popular Reply
Jan 31, 2022, 02:36 PM
Team Owner
Joined: Nov 2007
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From: Rochester, NY
Valves will close at certain RPM no matter what the setting, fuse pull keeps them open 100% of the time.
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2023 Corvette of the Year Winner - Modified
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Build the setup here as I have found it beneficial to have the option of loud or soft in my Homelink buttons.. can be built very inexpensively
https://www.corvetteforum.com/forums...ob-how-to.html
https://www.corvetteforum.com/forums...ob-how-to.html
Race Director
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From: Toronto, Canada
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Mine is set to track mode sound and for sure once i cross 2500 rpm or thereabouts it gets noticeably louder so something definitely shuts when taking it easy.
Tech Contributor
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From: Charlotte, NC (formerly Endicott, NY)
I know that the NPP can be disabled to allow free-flow exhaust with less restriction by using the menus on the screens, or by pulling fuse #42 (on a 2015 anyway).
Do those two techniques result in exactly the same result? I'm sure that pulling the fuse freezes the muffler valves open 100% of the time. If I set the menus to provide less restriction, does that also keep the valves open 100% of the time, or are there situations when the valves might need to close a bit?
TIA,
Larry
Do those two techniques result in exactly the same result? I'm sure that pulling the fuse freezes the muffler valves open 100% of the time. If I set the menus to provide less restriction, does that also keep the valves open 100% of the time, or are there situations when the valves might need to close a bit?
TIA,
Larry
Pulling the fuse opens the exhaust all of the time including during the poor sounding 4 cylinder operation.
Basically, pulling the fuse is worthless if you have an M7. It doesn't take much effort to avoid the less than 1500 rpm valve closing in 5th gear which is around 42 mph or lower. You can choose to run in 4th gear at those speeds or even 6th gear at 40 mph and the valves will be open. All clearly explained in the FSM except for the 5th gear closing.
Bill
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From: Boston
Pull the fuse and don’t look back. Neighbors be damned. I pulled the fuse at the 6 month mark and even the wife thinks the cold start sounds cool.
own the v8 and be proud pull the fuse and embrace the sound.
own the v8 and be proud pull the fuse and embrace the sound.
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Good info - having those valves open makes the car sound so good.
Racer
Joined: Mar 2013
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From: Houston
If you have an M7 the valves will be open all of the time except in 5th gear at engine rpms less than 1500. They will also close if you run the engine in Eco mode and the engine switches to 4 cylinder operation. The A8 can switch to 4 cylinder mode in all of the drive modes so the valves will close more often when driving an A8. I don't know if the A8 has a similar situation with one of its gears as the M7 has with 5th gear.
Pulling the fuse opens the exhaust all of the time including during the poor sounding 4 cylinder operation.
Basically, pulling the fuse is worthless if you have an M7. It doesn't take much effort to avoid the less than 1500 rpm valve closing in 5th gear which is around 42 mph or lower. You can choose to run in 4th gear at those speeds or even 6th gear at 40 mph and the valves will be open. All clearly explained in the FSM except for the 5th gear closing.
Bill
Pulling the fuse opens the exhaust all of the time including during the poor sounding 4 cylinder operation.
Basically, pulling the fuse is worthless if you have an M7. It doesn't take much effort to avoid the less than 1500 rpm valve closing in 5th gear which is around 42 mph or lower. You can choose to run in 4th gear at those speeds or even 6th gear at 40 mph and the valves will be open. All clearly explained in the FSM except for the 5th gear closing.
Bill
Safety Car
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From: Huntsville Alabama
The M7
In Track Mode will close them 1500 or below in 4th. open all else.
In Sport mode, will open them in 1-2-3. then if driving easy close in 4th-5-6-7. If still kind of accelerating it will keep them open in 4th, and close in 5-6-7th.
In Tour Mode, will be closed in 1-2-3-4-5-6-7th. UNLESS you accelerate pretty good (like think 60-75% throttle, and runt the gear out to 4000 or higher) then in touring mode they will open up, and stay open while you playing.. and once you let off, in what ever gear. they shut.
Eco & Wet mode the exhaust works like Tour mode.
I have Headers and OFf road X. so the changing can be drastic. Sport mode if fun at times just to let it explode when you randomly give it some. ha But most of the time open. I do I have M2W as well if I want to Pull the fuse.
In Track Mode will close them 1500 or below in 4th. open all else.
In Sport mode, will open them in 1-2-3. then if driving easy close in 4th-5-6-7. If still kind of accelerating it will keep them open in 4th, and close in 5-6-7th.
In Tour Mode, will be closed in 1-2-3-4-5-6-7th. UNLESS you accelerate pretty good (like think 60-75% throttle, and runt the gear out to 4000 or higher) then in touring mode they will open up, and stay open while you playing.. and once you let off, in what ever gear. they shut.
Eco & Wet mode the exhaust works like Tour mode.
I have Headers and OFf road X. so the changing can be drastic. Sport mode if fun at times just to let it explode when you randomly give it some. ha But most of the time open. I do I have M2W as well if I want to Pull the fuse.
Last edited by mittens; Feb 1, 2022 at 04:25 PM.
Le Mans Master
Joined: Aug 2015
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From: Toronto
The M7
In Track Mode will close them 1500 or below in 5th. open all else.
In Sport mode, will open them in 1-2-3. then if driving easy close in 4th-5-6-7. If still kind of accelerating it will keep them open in 4th, and close in 5-6-7th.
In Tour Mode, will be closed in 1-2-3-4-5-6-7th. UNLESS you accelerate pretty good (like think 60-75% throttle, and runt the gear out to 4000 or higher) then in touring mode they will open up, and stay open while you playing.. and once you let off, in what ever gear. they shut.
Eco & Wet mode the exhaust works like Tour mode.
I have Headers and OFf road X. so the changing can be drastic. Sport mode if fun at times just to let it explode when you randomly give it some. ha But most of the time open. I do I have M2W as well if I want to Pull the fuse.
In Track Mode will close them 1500 or below in 5th. open all else.
In Sport mode, will open them in 1-2-3. then if driving easy close in 4th-5-6-7. If still kind of accelerating it will keep them open in 4th, and close in 5-6-7th.
In Tour Mode, will be closed in 1-2-3-4-5-6-7th. UNLESS you accelerate pretty good (like think 60-75% throttle, and runt the gear out to 4000 or higher) then in touring mode they will open up, and stay open while you playing.. and once you let off, in what ever gear. they shut.
Eco & Wet mode the exhaust works like Tour mode.
I have Headers and OFf road X. so the changing can be drastic. Sport mode if fun at times just to let it explode when you randomly give it some. ha But most of the time open. I do I have M2W as well if I want to Pull the fuse.
Safety Car
Joined: Jul 2018
Posts: 4,303
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From: Margate, FL
This post covers lots of details of the NPP system:
https://www.corvetteforum.com/forums...ck-result.html
Due to noise laws even in Track mode the valves will close under certain conditions. Someone needs to put a GoPro down there and just film what happens along with a 2nd camera synced to the RPM.
https://www.corvetteforum.com/forums...ck-result.html
Due to noise laws even in Track mode the valves will close under certain conditions. Someone needs to put a GoPro down there and just film what happens along with a 2nd camera synced to the RPM.
Tech Contributor
Joined: Oct 1999
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From: Charlotte, NC (formerly Endicott, NY)
Haven't found any evidence of them closing in 3rd and 4th at any rpms unless running in Eco Mode then they will close in 4th gear. When in 4th put the car into Eco mode and run in cruise control at 30 mph and you will hear the exhaust go from slightly noisy to quiet and back to slightly noisy as the engine switches from V8 to V4 to V8. You don't want the valves open when the engine is running in V4 mode since the sound isn't very good. That means don't pull the fuse if you want to run in Eco Mode and if you don't want to run in Eco mode there is no need to pull the fuse.
Just because you can't hear a loud noise doesn't mean the valves are closed. At low throttle openings, there isn't much power being produced and the exhaust is quiet. You can hear the noise level change after you do a cold start, first, the exhaust is wake the dead loud followed by a lowering of sound level and once the engine is warm there is little noise even though you can look into the exhaust pipe and see the valve open.
Bill
Just because you can't hear a loud noise doesn't mean the valves are closed. At low throttle openings, there isn't much power being produced and the exhaust is quiet. You can hear the noise level change after you do a cold start, first, the exhaust is wake the dead loud followed by a lowering of sound level and once the engine is warm there is little noise even though you can look into the exhaust pipe and see the valve open.
Bill
Racer
Joined: Mar 2013
Posts: 327
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From: Houston
Haven't found any evidence of them closing in 3rd and 4th at any rpms unless running in Eco Mode then they will close in 4th gear. When in 4th put the car into Eco mode and run in cruise control at 30 mph and you will hear the exhaust go from slightly noisy to quiet and back to slightly noisy as the engine switches from V8 to V4 to V8. You don't want the valves open when the engine is running in V4 mode since the sound isn't very good. That means don't pull the fuse if you want to run in Eco Mode and if you don't want to run in Eco mode there is no need to pull the fuse.
Just because you can't hear a loud noise doesn't mean the valves are closed. At low throttle openings, there isn't much power being produced and the exhaust is quiet. You can hear the noise level change after you do a cold start, first, the exhaust is wake the dead loud followed by a lowering of sound level and once the engine is warm there is little noise even though you can look into the exhaust pipe and see the valve open.
Bill
Just because you can't hear a loud noise doesn't mean the valves are closed. At low throttle openings, there isn't much power being produced and the exhaust is quiet. You can hear the noise level change after you do a cold start, first, the exhaust is wake the dead loud followed by a lowering of sound level and once the engine is warm there is little noise even though you can look into the exhaust pipe and see the valve open.
Bill
Unless it's a weird gremlin only on my car, they will close under these conditions:
MPH - about 35 +/- a few
3rd or 4th gear
Sport mode
press in clutch and "goose" the throttle
You can hear the mechanics of the valves closing, and the volume drops dramatically, let the clutch out and they open back up
Again, maybe I have the one car in the world that does it, but there's no doubt that it does it.
Give 'er a try, I'd be interested to know if anyone else's does it. So far no one from the other thread would try it. It's not a huge deal, more of a curiosity than anything.
Racer
Joined: Mar 2013
Posts: 327
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From: Houston
Safety Car
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From: Huntsville Alabama