Folks mention closed, then open exhaust valves at certain RPM; yet no mention of which mode this does that in ?

On another note; what physical changes occur when the 'mode' **** is moved, say from Tour to Sport ? I know the MRC has shock wiring that affects the little micron fluid changes; so, is it a spring rate deal ? Being as non MRC shocks have no such wiring.

Thanks !

 

In for the answers.

 

Rtfb

 

Try this and post #18. https://www.corvetteforum.com/forums...post1590304017

Should have all your answers but long.

 

This thread covers the NPP functionality in detail as well:
https://www.corvetteforum.com/forums...ck-result.html

 

Rob gets a non-friendly response for above members. OK - Yes he can read the book.

 

Well... I would IF there was a 'Fn' book to read. Being as I'm seeking assistance as a perspective new owner, there isn't one. No need to be rude.

Besides, I doubt very seriously there's an owners manual guide to the physical changes in the spring rate. The posts, some folks were nice enough to post, does
answer the 'when' for the rpms on the NPP. Just looking for the other...

 

This might help, its from my 2014 manual - the newer cars are slightly different



As for the MRC spring rate - it is unchanged by the setting, only the fluid inside the dampers changes. This thread has good spring rate info:
https://www.corvetteforum.com/forums...ing-rates.html

 

JMII
Hey, appreciate that response. Curious, if the non-MRC cars have no wiring to the shocks, how that **** changes the rate ?

 

Non-MRC cars have standard dampers so the **** does nothing to the ride. That is why the table says "if equipped".

GM MISPRINT ALERT - it should also say "if equipped" in the exhaust section because if you don't have the NPP then the exhaust sounds the same in all modes.

Now keep in mind the steering, exhaust and dash cluster settings can be de-coupled from the **** if you wish. For example you can have the steering on Track all the time with display in Tour all the time while the exhaust is in Sport (model year dependent) regardless of how you twist the ****. The only thing truly locked to the **** is the suspension... well provided you have the mag-ride option. PTM (performance traction management) also requires the mag-ride. It has an additional table shown below:



I was actually surprised to learn that PTM wet and dry didn't use the Track suspension or steering setting. I incorrectly assumed all PTM modes were based on Track until someone corrected me and posted this graphic.

 

Apparently, the above table is also incomplete. The NPP exhaust is not set to Track when in PTM/Wet or PTM/Dry; nor does the PTM honor the 'Engine Sound Management' override setting. Throttle Progression is also progressive from PTM/Wet to PTM/Race (maybe implicit in the 'Traction Control' line above)

 

Curious as well......

 

 

There are different points when the valves open when you are in Tour or Sport. However, you can over ride those when you use the center display to access vehicle settings and go to engine sound management and select one of the sound programs there. They over ride everything except the exhaust setting for V4 operation. The valves will always close when the engine is commanded to operate in V4 mode (I suspect this is true even if you have an A8 with the Range Module installed as the exhaust is controlled by the chassis module not the ECM). If you select Track Mode the valves will be open all the time on an M7 car unless you select Eco and the engine then operates in V4 mode, they will open as soon as it goes back to V8 mode. With an A8 V4 mode can occur in any driving mode except when the transmission is put in Manual Mode. When you choose manual mode and have engine sound management set to Track the A8 valves will be open all the time as well. There is no such thing as partially open and there isn't any sound program they run to reduce noise at part throttle or lower speeds when you are in Track Mode those valves are open unless the engine is commanded to run in V4 mode. Any statement to the contrary contradicts the Factory Service Manual and my own experience with my car. If my stock car can have them open all the time then all of the C7s NPP exhausts can be open when operated the same way.

Bill

 

The valves will absolutely close on a C7 with a manual transmission even in track mode. I can hear them open close on my 2016. This is called the "hitch". Some people are more prone to hearing it than others. The fact that many people don't hear the change is testament to the programmers. The fact that the valves close was confirmed by Tadge. See the thread referenced above in post #5. From that thread "UPDATE 9/30/2015: I had the opportunity (surreal quite frankly) to meet Tadge and Harlan at a private event today. I spoke privately with the two of them for about 10 minutes, and one of my questions was the NPP programming. Tadge's comment was something like "If we didn't do it that way, we wouldn't be legal". Meaning that even in Track mode, the valves need to close for the dB requirements in the FMVSS pass-by noise regulations."

 

Thanks. I find it odd the way GM manages this. The assumption I had was all the PTM modes are Track related... after all the car must be in Track mode to activate PTM, so steering, suspension and exhaust should be in track mode. I could understand the suspension and steering dropping down to maybe Sport mode with PTM Wet to help with traction issues... but Tour? Way too soft for me for track duty. And not leaving the exhaust in Track mode? Oh well.

 

The spring rate does not / can not change. Leaf springs are non-adjustable. MRC changes the DAMPING rate of the shock absorbers by changing shock fluid viscosity by varying the magnetic field surrounding the fluid.

 

I've actually come to appreciate the clean design that the Corvette Engineering team has decided to embrace. This is readily apparent from the detailed technical thesis from this thead:
[ANSWERED] How do the Various PTM Modes Change Parameters When in Track Mode

PTM was designed exclusively for use on a race track. You are free to make use of these settings on surface roads but that's not what PTM is designed for.
PTM is all about gaining control over the various inter-operable parameters and presenting them in a cohesive step-function format to the race driver
PTM is all about presenting a gradual progression of driver control by progressive disablement of a coordinated set of 'safety' features, while at the same time minimizing the work load on the driver to optimize these individual ***** through trial-and-error.
Sure, the driver is free to experiment. Just don't choose PTM.

To put it bluntly, once you choose PTM, you are operating under 'GM Law'. Just don't fight it. Learn it. Embrace it.

 

My car doesn't have that hitch. I can have loud exhaust at very low rpms in the higher gears if I am applying throttle. When I set cruise control to 50 mph in 6th gear with the drive mode set to Eco the rpms are below 1700 and I can hear the exhaust switch to quiet when the engine goes to V4 mode and go back loud when the engine is operating in V8 mode. The switch from V4 to V8 usually comes with a significant sound pop if the car encounters a rise in the road surface. It is loud enough that I know people in other cars can hear it switch. When driving down the road in 6th or 7th gear at 70 mph the exhaust is loud enough that I have trouble hearing the radio.

I don't want to argue with Tadge but his engineers did write the description of operation in the Factory Service Manual and he has the disadvantage of being the boss and not necessarily familiar with how the system is actually working. The same way that Dave Hill at the 2004 Corvettes of Carlisle C5 intro told me the C6 Z51 brakes wouldn't fit on a C5 when they would easily adapt.

In large design and development projects the boss is left out of most design details as they have to spend so much of their time on the major items, such as budget, schedule overall design, marketing and running interference against higher up meddling. In most cases the boss isn't even the most qualified person to make design decisions. They just want to know that regulations were followed and don't really care how the regulations were met as long as the cost, schedule and design targets are also met. Miss one of those things and you will be invited to inform the boss what your get well plan is.

Bill

 

I don't know what to tell you Bill. My 2016 manual transmission with NPP, closes per the parameters in the other thread. When Spring get here, I will mount my GoPro so that it is looking at the exhaust and post a video.

I have have pulled the fuse and can hear the difference.

Having been involved in automotive as an engineer and engineering manager for 35 plus years, I can say manual writing falls to the low man on seniority . Mistakes happen.