NPP valve always open trial
Melting Slicks
Joined: Apr 2021
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From: Simi Valley, CA
2022 C8 of the Year Finalist - Modified
That helps but doesn't completely explain it. There is also a definite change in tone at idle - at least between Touring mode and Track mode. Is that just an open/closed phenomena? What about Stealth mode. If that is valves all the way closed at idle then what is Tour mode at idle?
I think there is something else going on here. It is probably the computers changing some combination of settings - I just haven't heard an explanation that satisfies me yet.
I think there is something else going on here. It is probably the computers changing some combination of settings - I just haven't heard an explanation that satisfies me yet.
Drifting
Joined: May 2010
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@smittydog How much disassembly is required to get to the actuators? I may try to attempt your mod to keep the NPP valves open. At least, it's reversible, if I wanted to restore it back. Have you experienced any additional error codes since making the mod? Thanks.
Thread Starter
Racer
Joined: Aug 2004
Posts: 482
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From: Florida, Tampa Bay
I reversed both of mine in about 90 minutes. Lift the rear of the car a few inches for clearance from tire to wheel well, remove mud flap, 2 torx screws behind mud flap, pull fender liner out and valve is right there. Furthest back screw is easier to reach from under exhaust through rear valance. If you jack. All the way up and remove tires there is more clearance but not necessary. Please do and let me know if it works. Plan to try mine again but gotta let the wife drive her car some more before I mess with it again.
Drifting
Joined: May 2010
Posts: 1,839
Likes: 390
I reversed both of mine in about 90 minutes. Lift the rear of the car a few inches for clearance from tire to wheel well, remove mud flap, 2 torx screws behind mud flap, pull fender liner out and valve is right there. Furthest back screw is easier to reach from under exhaust through rear valance. If you jack. All the way up and remove tires there is more clearance but not necessary. Please do and let me know if it works. Plan to try mine again but gotta let the wife drive her car some more before I mess with it again.
Race Director
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I have a Borla exhaust that still uses the AFM and NPP valves. Using MyMode and just changing the exhaust setting from Tour to Sport to Track, there is an appreciable difference between each setting and also between all of them and the Stealth setting in Weather mode. Based on that it seems that the valves must have variable position - not just open and closed.
So - he is talking about the Borla system, and not the stock system. As I mentioned, either in this thread or similar one, the information regarding the control of the valves in the service manual, in both the description and the schematics, says that the control signal is pulse width modulated. This type of control would allow for variable positions, not just open or closed, if the valves were capable of responding to the signal that way. We also know that the Z06 will have variable positions. We also know (from the service manual) that the current description refers to the valves being commanded only two positions - open or closed. Perhaps (speculating now) the information for variable positions is already there, and the Borla valves are designed to respond to that, but perhaps the stock system valves are just open or closed. If this speculation turns out to be true, it would explain why you can hear a more dramatic difference with your Borla system. Check the video and see what you think.
Last edited by Andybump; May 7, 2022 at 12:02 PM. Reason: fixed the link
Melting Slicks
Joined: Apr 2021
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From: Simi Valley, CA
2022 C8 of the Year Finalist - Modified
That link just takes me to the Borla web site with some axle-back exhaust systems shown. I'd like to see the video you're talking about - can you provide a better link or instructions on where you found it. Is it one of the two Borla C8 videos on YouTube?
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Melting Slicks
Joined: Apr 2021
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From: Simi Valley, CA
2022 C8 of the Year Finalist - Modified
Thanks. I watched that video some time ago - it was one thing that sold me on Borla - but I didn't really catch the part about the different valve positions. Very interesting. Makes me wonder if you are correct - that the computer sends modulated signals but the NPP exhaust doesn't take advantage of them. I'm going to see if the Corvette mechanic at my dealer can shed any light when I take my car in next week.
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Thanks. I watched that video some time ago - it was one thing that sold me on Borla - but I didn't really catch the part about the different valve positions. Very interesting. Makes me wonder if you are correct - that the computer sends modulated signals but the NPP exhaust doesn't take advantage of them. I'm going to see if the Corvette mechanic at my dealer can shed any light when I take my car in next week.
Race Director
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From: Garden Valley CA
OK - to revive this discussion - I just reviewed the video on the Borla website. He actually says that there are valve positions other than open and closed, at 6:16 in the video:
https://www.youtube.com/watch?v=ptg8JWUfiCg&t=352s
So - he is talking about the Borla system, and not the stock system. As I mentioned, either in this thread or similar one, the information regarding the control of the valves in the service manual, in both the description and the schematics, says that the control signal is pulse width modulated. This type of control would allow for variable positions, not just open or closed, if the valves were capable of responding to the signal that way. We also know that the Z06 will have variable positions. We also know (from the service manual) that the current description refers to the valves being commanded only two positions - open or closed. Perhaps (speculating now) the information for variable positions is already there, and the Borla valves are designed to respond to that, but perhaps the stock system valves are just open or closed. If this speculation turns out to be true, it would explain why you can hear a more dramatic difference with your Borla system. Check the video and see what you think.
https://www.youtube.com/watch?v=ptg8JWUfiCg&t=352s
So - he is talking about the Borla system, and not the stock system. As I mentioned, either in this thread or similar one, the information regarding the control of the valves in the service manual, in both the description and the schematics, says that the control signal is pulse width modulated. This type of control would allow for variable positions, not just open or closed, if the valves were capable of responding to the signal that way. We also know that the Z06 will have variable positions. We also know (from the service manual) that the current description refers to the valves being commanded only two positions - open or closed. Perhaps (speculating now) the information for variable positions is already there, and the Borla valves are designed to respond to that, but perhaps the stock system valves are just open or closed. If this speculation turns out to be true, it would explain why you can hear a more dramatic difference with your Borla system. Check the video and see what you think.
Race Director
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From: Garden Valley CA
Race Director
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Good point. He says nothing about the actuators. I think Jerry U mentioned that the actuators are "stepped motors" which I think means they are capable of different positions - but Jerry also I think believes they only have two commanded positions.
Melting Slicks
Joined: Apr 2021
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From: Simi Valley, CA
2022 C8 of the Year Finalist - Modified
I'm so confused
Race Director
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From: Garden Valley CA
It could be tricky to get good sound out of a modulating system, you don't want a squeaker or something. And the system may need to be more robust to hold the valve in a partially open position.
Race Director
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Yes, fully open or fully closed would require less force (or whatever) to hold it in that position. Partially open would have to fight the flow of exhaust gas. I had to look up what a step motor was - but it is what it sounds like -- "A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any position sensor for feedback". Something that could be commanded to a position that it would hold. I was envisioning just 4 positions - closed (stealth), open some for tour, open more for sport, and full open for track. Appropriately switched if necessary to meet those bypass standards. I would assume that the Borla systems and other aftermarket systems dont have to meet the standard. But, the GM Borla may have to. Anyway, your point about re-using the actuator seems to make all this a moot point - unless the base NPP system has different positions - which we thought was not the case.
Drifting
Joined: May 2010
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The GM version is made to GM provided specs and standards according to Borla. You can only get it through GM. Borla doesn't list it on their site. The exhaust tip options are also slightly different compared to what Borla normally offers on the S-Type and ATAK models.
Thread Starter
Racer
Joined: Aug 2004
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From: Florida, Tampa Bay
Any one else dumb enough to try this besides me? I unhooked em and hooked em up once and was hoping someone else would do a beta test for me. I'm going to have to try it again sooner or later either way.
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I have a Borla exhaust that still uses the AFM and NPP valves. Using MyMode and just changing the exhaust setting from Tour to Sport to Track, there is an appreciable difference between each setting and also between all of them and the Stealth setting in Weather mode. Based on that it seems that the valves must have variable position - not just open and closed.
I haven't tried a similar comparison in my C8.
Last edited by Red Mist Rulz; May 18, 2022 at 05:00 PM.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
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From: NE South Carolina
^^^
My C7s were exactly the same could hear the distinct change in mine
as they were in Track (at ~1700 rpm.) Harder to tell in the C8 driving in Z Mode (no V4) and Manual.
This controversy did not end with the C7's until folks added Mild to Wild (or made their own) and at highway speeds flipped to open and they could hear the drone. Although the C6 system is different, I installed a switch to lock open. At highway speeds had to allow them to shut or the drone was objectionable.
My C7s were exactly the same could hear the distinct change in mineas they were in Track (at ~1700 rpm.) Harder to tell in the C8 driving in Z Mode (no V4) and Manual.
This controversy did not end with the C7's until folks added Mild to Wild (or made their own) and at highway speeds flipped to open and they could hear the drone. Although the C6 system is different, I installed a switch to lock open. At highway speeds had to allow them to shut or the drone was objectionable.