MoabC7

I have tried to read all the threads re. the NPP Performance Exhaust, Driving Modes and scoured the Owner Manual (why isn't it Owner's Manual ?) for info on how the two should work together.

My experience with our Z51 with NPP is that even in Track mode, the NPP during start-up sounds wonderful and throaty. But, once she warms up, the exhaust goes much quieter. Personalization for the Engine Sound Management is set to OFF.

This behavior is one of the biggest disappointments with our new C7. IMO, our C6 with Mild-2-Wild was way better at slower speeds. That said, the C7's highway cruise level is perfect. And we typically drive in Sport or Track most of the time.

Has anyone tried pulling the two fuses for Exhaust Valve 1 and 2? Since I have not come across anything about them, nor know what they affect, I am hesitant to pull and try.

And the Owner Manual really sucks for so many things. For example, it doesn't even come close to explaining what the exhaust is doing, what to expect in various modes, or how it works.

Hopefully Paul's, talon90, future "Tech Tips" pdf file will address some of this.

talon90

I don't have NPP on my car so I can't verify any of the information contained below. The only additional information I can offer currently is what is provided to dealerships in the form of a bulletin (PI1056) that was released on September 17th:


Exhaust Tailpipe Flow Control Valve System — RPO NPP
 
The exhaust tailpipe flow control system is used to tune the exhaust note for high performance vehicles. This vehicle is equipped with two tailpipe exhaust valves. One in the left tailpipe and one in the right tailpipe. Each exhaust tailpipe valve is installed in the low restriction exhaust path of a dual outlet muffler, near the exhaust tip.

When a tailpipe exhaust valve is open, the low restriction exhaust path is opened to the atmosphere, and the exhaust note becomes more aggressive.

An output circuit from the chassis control module is used to control the actuator that opens the left and right exhaust tailpipe valves. The exhaust flow control valve opens and closes when the chassis control module commands the actuator by pulse width modulation of the control signal.

To provide a more aggressive exhaust note when the vehicle is started, the exhaust tailpipe valves are opened during an engine crank event during specific modes of operation if that option is available.

Once the engine is running, accelerator pedal position, transmission gear and engine speed are used to determine the commanded state (open or closed) of the exhaust tailpipe valves.

There are four specific exhaust performance modes that result in different behavior of the exhaust tailpipe valves. These modes are:

• Weather/Eco Mode: Exhaust tailpipe valves will be closed at all times when the engine is running.
• Tour Mode: Exhaust tailpipe valves are closed when the engine is idling and during normal/non-aggressive driving. Valves open during aggressive driving.
• Sport Mode: Exhaust tailpipe valves are open when the engine is idling and during most driving scenarios.
• Track Mode: Exhaust tailpipe valves are open at all times.
It is possible to personalize the exhaust sound. Select the Driving Mode menu and the following will be displayed:
• Exhaust
• Steering
Select Exhaust. This controls how robust or quiet the engine will sound. Select:
• Auto
• Stealth
• City
• Tour
• Sport
• Track
• Off

MoabC7

Thanks Paul.

Unfortunately, the bold faced options are in fact not available. My understanding is this changed about the time regular production was started. As far as I know, no owner vehicles have those additional programming options.

When we finally get to see the shop manual, maybe we can sort out how this system is suppose to work. Personally, I think pulling the fuses to the exhaust will give us full time throatiness. I also think that something in the variable valve exhaust system (NPP) or something else upstream is changing, closing somewhat or whatever since myself and others have reported less "robust" exhaust tone, even in Track Mode, once the engine warms up.

Anyone with any documented/documentation information, please speak up.

Bill

talon90

That could make sense. There is another set of valves on the engine side of the mufflers for better balance when the car is in Eco mode. They may be coming in to play at other times depending upon what feedback the computer is giving/getting.

C7_Z06

So it looks like the NPP-equipped cars have the same ESM choices as the non-NPP cars. http://forums.corvetteforum.com/c7-g...ways-open.html

Here's mine (no NPP):



I still have the capability to keep my middle (and the only one present on non-NPP cars) exhaust valves open all the time... same words Harlan Charles told me during last week's Precision Stingray event when I asked him.

MoabC7

Didn't realize that. That could explain C7-Stingray's comment about non-NPP Stingrays having valves per Harlan Charles. I would think standard non-NPP units would not have the variable valves we see on the exhaust side of the mufflers.

That said, I wonder if the NPP owners have been handed a "neutered" exhaust system since the options you quoted are not present? That could explain things. And it sounds like a software change would be the cause that has possibly restricted NPP flexibility as was originally promised.

Taking this a step further, it raises the question as to whether or not pulling the fuses of Exhaust Valve 1 & 2 would impact the engine side valves and perhaps ECO or other Modes.

13brv3

My understanding is that all cars have the engine side valve, because it's needed when the car goes to V4 mode. I don't think that should be changing unless you're switching between V4 an V8 modes.

I started a thread a couple weeks ago asking if anyone had figured out how the NPP actually worked on the C7, but it doesn't seem anyone knows. It's not as easy as the vacuum operated valves on the C6, which were either open or closed. Now the valves are operated by an electric motor, so they can be varied between open and closed, presumably in many steps.

Someone may have to hang a GoPro back there looking into the exhaust to find out

Rusty

MoabC7

And that would be just for starters. We really need some GM documentation which explains how this whole system works. And you are right it is not what we had on the C6. Old school vs. new school.

13brv3

Documentation would be nice of course

If I had to bet, I'd say they made sure to design the hardware to allow anything they want to do with the valves. Assuming they're variable opening, and electrically controlled by software, then the hardware engineer did his job.

I'd further bet (guess) that the software engineer ran out of time, and they had to release the system with a more limited control scheme than they had planned, which is also indicated by the fact that the manual shows modes that don't exist.

The good news would be that they can reflash the firmware at any time, and add the new modes once they're finished. I'd bet tuners will be able to figure this out eventually as well.

Cheers,
Rusty

ldepalma

I've been saying for two weeks now (that's how long I've had my C7) that the C6 with NPP was and is much louder then the C7 with NPP. To pin point it in two ways, one is, the back pressure with the smaller exhaust in both in diameter and the tips themselves, makes the C6 louder and the drone that you got while driving down the rode in the C6 was very noticeable (I liked it myself) you don't get that sound at all in the C7. Secondly, there is a youtube video of the mild to wild on a C6 (many to be exact) that when you rev the C6's it blows the C7's sound away, period. The C7 is by no means quite but just not as loud as the C6 IMO anyway....

MoabC7

Don't miss the drone at all especially for cross-country driving, which is why I loved the Mild-2-Wild. Had it both ways.

But agree with you 100%.

Dusty Starbucks

If they are using a PWM to control the valves, then the valve is very likely variable and not just on/off, but with several in-between steps.

Someone said two fuses, likely one is for the V4 valve and the other is for the two valves at the tips. One would think the fuse for the tip side would be larger amperage, but I am not sure. Either way, take one out and see what happens. I would expect it fails open, which would mean taking the fuse out will leave it open. If taking it out has no effect on the tip side valves, try the other fuse. It's not going to hurt anything to try.

MoabC7

Managed to get a question into Tadge Juechter on Autoline After Hours re. the Performance Exhaust. Didn't answer all of the question but the one bit of info I gleaned out of his response was that the front set of valves are more of an orifice design primarily to eliminate a four cylinder sound when in ECO. And the rear for the more robust sound. He implied that the Track mode should be really loud. Both sets of valves are electrical, as we knew.

The plot thickens.

Glen e

I have 3000 miles on my car with NPP. As far as I can tell, you cannot keep them open 100% of the time, even if set in track mode with the option on the screen set to "off". It still closes down after you accelerate and move to a cruise position no matter what you do....

0-60B4U

Seems to be the way mine operates. It is also much louder at start-up and when cold than when it has been driven for a period of time.

Glen e

same here

Promind

mine too

MikeyTX

Somehow, after reading through all this, I'm glad I opted not to go with the NPP. I have a gut feeling that given time Borla, Corsa and, Billy Boat will bring to market truly great sounding axle back systems.

Champ3143

Well I can't cancel that off my options!! If there is no real difference in sound it does not make sense to spend my hard earn on it. Thanks!! You guys saved me 2 grand.

Glen e

where are you getting there is no diff in sound???...there is a HUGE DIFF in sound...we are all talking about the diff modes and how it's controlled...