Keeping NPP full open
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Instructor
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From: Nashville, TN
Keeping NPP full open
Will unplugging the NPP valves and wiring in NPP simulators keep the factory NPP full open without throwing a code? Making sure I'm understanding that right, thanks in advance! Little bit more complicated then with the C6/C7.
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Instructor
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From: Nashville, TN
Melting Slicks
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From: Nashville, TN
I put an NPP on my non-NPP C8 and can confirm that the springs keep the NPP valves open. The actuators close them when necessary, so if the actuators are bypassed (unplugged and replaced with simulators to keep from throwing a code) I can confirm they will be open all the time.
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Just be aware, if the engine/sound is set to Track or Sport, which happens in Track Driver Mode and Sport Driver Mode, and can be selected in MyMode or Z-mode, the valves are open almost all the time. They close under certain conditions to meet Federal Bypass Standards - but its not easy to detect those cases in practice.
Here is thread about an experiment to keep the valves open all the time. The result for the OP is that it was hardly distinguishable from just setting the engine/sound to Track.
https://www.corvetteforum.com/forums...ld-2-wild.html
Here is thread about an experiment to keep the valves open all the time. The result for the OP is that it was hardly distinguishable from just setting the engine/sound to Track.
https://www.corvetteforum.com/forums...ld-2-wild.html
Thread Starter
Instructor
Joined: Jul 2018
Posts: 145
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From: Nashville, TN
Just be aware, if the engine/sound is set to Track or Sport, which happens in Track Driver Mode and Sport Driver Mode, and can be selected in MyMode or Z-mode, the valves are open almost all the time. They close under certain conditions to meet Federal Bypass Standards - but its not easy to detect those cases in practice.
Here is thread about an experiment to keep the valves open all the time. The result for the OP is that it was hardly distinguishable from just setting the engine/sound to Track.
https://www.corvetteforum.com/forums...ld-2-wild.html
Here is thread about an experiment to keep the valves open all the time. The result for the OP is that it was hardly distinguishable from just setting the engine/sound to Track.
https://www.corvetteforum.com/forums...ld-2-wild.html
Not sure the logic in the C8Z06, but I'm more than happy to give it a shot. Very easy and worst case I have them on hand if I go aftermarket exhaust!
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Not sure if the logic is the same, but I experimented quite a bit with the C7 and yes it's the same 98% of the time. If I remember correctly, it was idling and low throttle below around 35mph that they closed. It was worth it to me to keep the fuse pulled on my C7. What's great is being able to select softer modes, like weather, and retain full volume.
Not sure the logic in the C8Z06, but I'm more than happy to give it a shot. Very easy and worst case I have them on hand if I go aftermarket exhaust!
Not sure the logic in the C8Z06, but I'm more than happy to give it a shot. Very easy and worst case I have them on hand if I go aftermarket exhaust!
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Thread Starter
Instructor
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From: Nashville, TN
Old thread, but figured I'd update for anyone else's knowledge. The simulators work great at keeping them full open. There's several instances where there's a difference between track mode and NPP unplugged. Rapidly coming off full throttle will give more pops and bangs with NPP unplugged, low and mid constant rpm sound is louder and much more present with NPP unplugged, and finally sometimes cold starts are louder with NPP unplugged as it'll pop/burble when the engine is truly cold.
It's worth it to me for the additional pops and burbles, I'm giving up stealth mode, but the extra engine sound in certain scenarios is worth plugging in simulators. The one time it's annoying is 6th gear at 75mph it drones, but drop to 8th and it's completely gone and very quiet.
It's worth it to me for the additional pops and burbles, I'm giving up stealth mode, but the extra engine sound in certain scenarios is worth plugging in simulators. The one time it's annoying is 6th gear at 75mph it drones, but drop to 8th and it's completely gone and very quiet.
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Old thread, but figured I'd update for anyone else's knowledge. The simulators work great at keeping them full open. There's several instances where there's a difference between track mode and NPP unplugged. Rapidly coming off full throttle will give more pops and bangs with NPP unplugged, low and mid constant rpm sound is louder and much more present with NPP unplugged, and finally sometimes cold starts are louder with NPP unplugged as it'll pop/burble when the engine is truly cold.
It's worth it to me for the additional pops and burbles, I'm giving up stealth mode, but the extra engine sound in certain scenarios is worth plugging in simulators. The one time it's annoying is 6th gear at 75mph it drones, but drop to 8th and it's completely gone and very quiet.
It's worth it to me for the additional pops and burbles, I'm giving up stealth mode, but the extra engine sound in certain scenarios is worth plugging in simulators. The one time it's annoying is 6th gear at 75mph it drones, but drop to 8th and it's completely gone and very quiet.
Reminded of my C6 where it was easy to install a simple switch on the console to keep NPP valves open. I kept them open all the time except on the highway around 60 to 65 where the drone was so bad in 6th gear (top in my standard shift.) I had to flip the switch and let them close
My overall feeling is my 2014 C7 Z51, 2017 Grand Sport NPP were not as "good a sound" as the C6. And the C6 with NPP open was not as good as my 1st Vette, a 1988 where I added FlowMaster mufflers. Heck even the FlowMaster on my S-10 truck V6 sounded better than my C6.
My 2020 C8 Z51 NPP was even quieter. Tadge discussed the reasons even with metal headers. The short coupling from engine to mufflers is a factor. Plus they worked hard to insulate engine noise from the cabin. Like using very thick glass between the two, three times thicker than the windshield.
My E-Ray even appears somewhat quieter! Now standing outside the car it's not bad. BUT I drive roof on windows always up. I hear the NPP at WOT but with the E-Ray that is only a few seconds and your past triple digits. Now I have the sound system playing >1500 songs in shuffle mode 98% of the time. Pretty loud to drown out tire and road noise. (I do have NPP set to Track in the two drive modes I use Z-Mode and MY Mode.)
Last edited by JerryU; Aug 9, 2025 at 02:53 PM.
Thread Starter
Instructor
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From: Nashville, TN
Good input! Thanks.
Reminded of my C6 where it was easy to install a simple switch on the console to keep NPP valves open. I kept them open all the time except on the highway around 60 to 65 where the drone was so bad in 6th gear (top in my standard shift.) I had to flip the switch and let them close
My overall feeling is my 2014 C7 Z51, 2017 Grand Sport NPP were not as "good a sound" as the C6. And the C6 with NPP open was not as good as my 1st Vette, a 1988 where I added FlowMaster mufflers. Heck even the FlowMaster on my S-10 truck V6 sounded better than my C6.
My 2020 C8 Z51 NPP was even quieter. Tadge discussed the reasons even with metal headers. The short coupling from engine to mufflers is a factor. Plus they worked hard to insulate engine noise from the cabin. Like using very thick glass between the two, three times thicker than the windshield.
My E-Ray even appears somewhat quieter! Now standing outside the car it's not bad. BUT I drive roof on windows always up. I hear the NPP at WOT but with the E-Ray that is only a few seconds and your past triple digits. Now I have the sound system playing >1500 songs in shuffle mode 98% of the time. Pretty loud to drown out tire and road noise. (I do have NPP set to Track in the two drive modes I use Z-Mode and MY Mode.)
Reminded of my C6 where it was easy to install a simple switch on the console to keep NPP valves open. I kept them open all the time except on the highway around 60 to 65 where the drone was so bad in 6th gear (top in my standard shift.) I had to flip the switch and let them close
My overall feeling is my 2014 C7 Z51, 2017 Grand Sport NPP were not as "good a sound" as the C6. And the C6 with NPP open was not as good as my 1st Vette, a 1988 where I added FlowMaster mufflers. Heck even the FlowMaster on my S-10 truck V6 sounded better than my C6.
My 2020 C8 Z51 NPP was even quieter. Tadge discussed the reasons even with metal headers. The short coupling from engine to mufflers is a factor. Plus they worked hard to insulate engine noise from the cabin. Like using very thick glass between the two, three times thicker than the windshield.
My E-Ray even appears somewhat quieter! Now standing outside the car it's not bad. BUT I drive roof on windows always up. I hear the NPP at WOT but with the E-Ray that is only a few seconds and your past triple digits. Now I have the sound system playing >1500 songs in shuffle mode 98% of the time. Pretty loud to drown out tire and road noise. (I do have NPP set to Track in the two drive modes I use Z-Mode and MY Mode.)
E-Ray, 3LZ, ZER, LIFT
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From: NE South Carolina
I agree, it's a shame that it's not as easy! I would love a mild to wild setup or even just the simplicity of replacing an under hood fuse. I've since compared the differences three times and I get more pops/burbles out of the LT6 off throttle without the valves. I'd love to retain stealth mode for startup. Mild to wild sells a controller, but it's much more involved than in the past and involves tearing out the waterfall and messing with the fuse box.
Thought is was discontinued years ago
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I'm not saying it works, just that is listed there - and other sources too.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,858
Likes: 12,289
From: NE South Carolina
Interesting. Recall when folks were trying to get their money back because of it tripping CELs and couldn’t. If it actually works, keeps NPP butterfly’s open and doesn’t trip a CEL, funny we have not seen posts to that effect.
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I know! I can't recall any post discussing its successful installation.