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I have npp set to open all the time. In sport mode. When driving exhaust is sometimes loud and then quiet. I thought, when set to open , exhaust was unrestricted. Any help

Tks Jack
 

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They are open, but the v4/v/8 valve are still opening and closing on an auto trans....

And I personally think- just my opin- that all the modes , no matter what trans, and even locked open, the valves close at hi speed interstate.....
 

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Wondering out loud here...What would happen if the electrical connection @ the valves were unplugged with the valves open? I was just wondering if this action would trip a CEL or perhaps worse, adversely effect engine management? Sooner or later I bet someone will try and see.
 

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Chip I've been thinking about that for a while. When it closes at cruise, I cringe at the silence.
 
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Chip I've been thinking about that for a while. When it closes at cruise, I cringe at the silence.
JC; It looks like there are indicator arms on the valve actuators that will help determine the position of the valves. Seems like it's a matter of un-plug and play! I still wonder if this will trip a CEL though? Why not try it?

npp2.jpg
 

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Imho, it would appear that the DI, VVT and the AFM Systems, which control the exhaust valves, rule. In order, for GM, to meet EPA requirements of 28 or 29 mpg, the engine systems are trying to be as efficient as possible, under light loads (little exhaust noise). Under full acceleration, the both sets of valves open (ah, really good exhaust sounds). It would be nice to be able to override the system that controls of the exhaust valves, but that system isn't set up to allow that to happen (neither is GM). But what do I know, my baby is at 3300 "Scheduled For Production". Looking forward to testing out my theory.
 
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Imho, it would appear that the DI, VVT and the AFM Systems, which control the exhaust valves, rule. In order, for GM, to meet EPA requirements of 28 or 29 mpg, the engine systems are trying to be as efficient as possible, under light loads (little exhaust noise). Under full acceleration, the both sets of valves open (ah, really good exhaust sounds). It would be nice to be able to override the system that controls of the exhaust valves, but that system isn't set up to allow that to happen (neither is GM). But what do I know, my baby is at 3300 "Scheduled For Production". Looking forward to testing out my theory.
Doesn't the Engine Sound Management feature described on page 5-42 of the owners manual allow you to turn off the exhaust "auto" feature thus leaving the exhaust valves open in all modes and all driving conditions?
 

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No ...auto, just attaches the sound to the mode
Track - open
Sport- open
Tour, Eco, wether - closed

In general

Turn it to off and its open all the time
 

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Thanks. Just picked up my new C7 yesterday and now that I have a sense of how loud it is with the valves open in Sport mode (not too loud, great sound), I'm going to set it for the valves to be open all the time. I was concerned that it would have a loud drone on trips that could get annoying but at highway speeds (due to AFM I guess), it runs pretty quiet. (Automatic transmission)
 

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Well that's some thing not explained very well...at highway speed even if you have it set to be open, they close up to elim drone.

Doo yourself a favor, get the manual, the infotainment book and a six pack, go turn on the ignition and sit in the car for an hour and choose every option in the display. You'll know more than asking here. The manuals are wrong on a few things.....
 

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Ha that's the best advice I've read today. Or if you don't have your car yet get a six pack, the manual, and a lawn chair.
 

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Well that's some thing not explained very well...at highway speed even if you have it set to be open, they close up to elim drone.

Doo yourself a favor, get the manual, the infotainment book and a six pack, go turn on the ignition and sit in the car for an hour and choose every option in the display. You'll know more than asking here. The manuals are wrong on a few things.....
Not to "drone" on about this; So the valves are not open "all the time" if you turn the engine sound management off?
 

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I would not recommend messing with the forward set of valves (the AFM valves).

In AFM/DOD active with an open exhaust there is a horrendous burble that yo will not enjoy.
Ask the Camaro auto guys about this when they run a non resonated cat back without disabling AFM/DOD.

The rear most valves are the valves that you have full control of through the infotainment system and the forward valves remain controlled by the ECM/PCM as far as I'm aware.
 

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I would not recommend messing with the forward set of valves (the AFM valves).

In AFM/DOD active with an open exhaust there is a horrendous burble that yo will not enjoy.
Ask the Camaro auto guys about this when they run a non resonated cat back without disabling AFM/DOD.

The rear most valves are the valves that you have full control of through the infotainment system and the forward valves remain controlled by the ECM/PCM as far as I'm aware.
Tnx Crawler. By the "rear most valves" do you mean the ones with the performance exhaust option? If those are the only ones controlled thru the infotainment system, then why is the infotainment system (off/auto) feature available/operable even when the car is not equiped with the optional performance exhaust?
 
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