rectifyer2000

OK, I've ready every thread I can find about the exhaust/muffler valves (AFM, NPP or whatever they are called), with the A8. Apparently, there is no on-board control that keeps them open at lower RPM's (track mode, supersonic mode, hyperspace mode...) in the A8.

So, I want to manually control the valves to keep them open at ALL times, or closed at ALL times. You know, press a button and they open and stay open or press a button to close them and they stay closed. Does anyone have a solution to this on the new Z?

I've currently got the C6 Z06 bi-modes and installed a vacuum controller that allows me to control the valves manually, exactly as stated above, with the press of a button. But so far, I can't find any info., device or method that will allow me to do this when my 2016 arrives.

Anyone know?

RoketRdr

The only way is to have the AFM tuned out. You could keep the AFM valves from closing but you won't be able to keep the engine from going into V4 mode. It would sound like crap. Only other option is to keep the car in manual shift mode and manually stay in a lower gear to keep RPM'S up.

rectifyer2000

V4 Mode.....hmmmm, yes, I can imagine that might sound weird - I wonder. I'm certainly not interested in forcing the car into lower gears just to have the exhaust sound good. So I'm wondering what cars with Corsa or other exhaust with no valves sound like in V4 Mode. Anyone?

xp800

As Roket said, there is no AFM valve override, nor would you want one. They need to close in V4. The A8 goes into V4 mode in all modes, except M (paddle shift).

Getting rid of AFM mode is either a tune or the Range Technology plug (goes in the OBDII port). The Range option is non-invasive and does not alter the permanent car programming. So no warranty issues. On sale typically $160.

The NPP are entirely electric and can be completely bypassed by pulling the NPP fuse, but you can't re-enable them from the cockpit. Takes 20 seconds to manage the fuse.

If you had searched in C7 tech there are a number of threads on NPP control options. One is a simple switch bypass, the other is a full controller like you describe. Both these are for NPP only, not AFM.

https://www.corvetteforum.com/forums...e-control.html

https://www.corvetteforum.com/forums...-retrofit.html

rectifyer2000

The AFM system is something I don't want to mess with. The only thing I want control over is the sound of the exhaust (NPP). People are using the term AFM in a way that makes it seem like an additional set of valves to control the sound. I'm pretty sure there is only one set of valves (NPP) that controls the exhaust sound, which happens to be linked with the AFM system, opening and closing the NPP. Right?

I'd love to see a cut-away/schematic of the muffler system. The old system was a pair of butterfly valves, located after the muffler just before the tailpipe. The new system appears to be located before the mufflers. Anyway, I want to control the sound of the exhaust (NPP), regardless of what mode the AFM is in. I guess the fuse is the way to go but others have commented that the fuse only works on the M7, not the A8. Which fuse for the A8?

foreverfuelie

There are cut-a-way pictures of the exhaust system that are in various threads when the Z was first introduced. I'm attaching (if it works) a diagram that was also published the explains the NPP system. You will note there are two (2) sets of valves (look for the black box actuators) one set (the AFM) of valves is before the mufflers, the second set (NPP) is behind the mufflers. Hope this helps.

xp800

First, there are two sets of valves for cars with NPP exhausts...mostly. There are folks with Z06 who have reported no AFM valves in cars produced in the second half of the 2015 run. There are NO reports of Stingray NPP cars having ONLY NPP valves like the recent Z06.

The cutaway above is from the Z51 NPP car. There are even pictures of a Z06 car with both sets of valves in the initial show circuit. But unless you have a newer Z06, plan on having both AFM and NPP.

That said, the reason the A8 folks (like me) report limited value in pulling the NPP fuse -only- is due to the incessant V4 operation. When in V4, the AFM valves close and the exhaust goes quiet. Same level of quiet as if the NPP valves close. So the AFM valves mask the NPP valves being forced open, negating the effect.

The bottom line is that if you want your A8 to make good V8 sounds ALL the time, you need to get rid of AFM mode AND pull the NPP fuse.

NPP fuse: #41 for 2014, #42 for 2015/2016

FWIW, I and others have done a bit of thinking/testing on this stuff...:

https://www.corvetteforum.com/forums...ck-result.html

rectifyer2000

Excellent, this totally clears it up for me - Thanks! My 2016 Z will be built next week, so I wonder if it will have the AFM and NPP valves. I wonder why GM felt the need to add the AFM valves? What a PITA! It almost seems cleaner and easier to just replace the mid-pipe and mufflers with aftermarket components - ditching the entire axle-back, over-valved system.

I'll probably eventually have headers, but really don't want the exhaust obnoxiously loud, and it's nice to have the option to go into stealth mode....

RoketRdr

The AFM valves are on the A8 cars. M7 cars don't have them.

foreverfuelie

Tain't necissarily so. I and two other friends with A8 Z06's (two stage one and one stage three/Z07) do not have the AFM valves either. GM may have come up with another method on all latter produced Z's.

rectifyer2000

I've heard this. When did you guys get yours? Any 2016 guys out there check out your system yet? The AFM valves seem redundant and I'm hoping GM scratched them!!

Destrukt

Just get some B&B Bullets and call it a day!

xp800

For the single-valve Z06, it would be a great experiment to pull the NPP fuse and see if you get a CEL. In an AFM valve equipped car, if the valve actuators are unplugged or fuse pulled, this will trigger a CEL. NPP not so. Which makes me wonder what happens in the single valve systems. So if someone with a single valve Z06 pulls the fuse and can get V4 mode to engage, we will soon know a definitive answer. The unbaffled V4 tractor sound can't be ignored... Someone with a NPP valve only Z06 please try pulling fuse #42 in the front fuse box and report back!

I believe that the Z06 can get away with a single valve because ALL of them come with NPP exhaust. The Stingray has NPP as an option, which is an axle-back change, yet ALL Stingray must have AFM. I think managing the complexity of a single valve solution for the Stingray given the two exhaust options is the issue (wiring, programming).

That said, the baffling function of the NPP valves alone in V4 mode must be sufficient for the Z06. Cheaper too...

I also want to revise my "incessant AFM mode" comment (which applies for the Stingray) for the A8 in the Z06 application. By all reports the Z06 A8 AFM has the opposite behavior of the Stingray: it rarely engages unless perfectly flat or going down hill. So the exhaust going quiet because of V4 mode is much less prevalent. This however does NOT alter the undesirable NPP closure/actuation in the "loud" modes like Track.


CF user meyerweb tested very extensively and came up with a quite plausible reason for the NPP closure profile even when ESM set to Track: US pass-by noise regulations.

Post #252 in my NPP thread:

https://www.corvetteforum.com/forums...post1589760867

foreverfuelie

Two of us had our Z's assembled on the same day (20 cars apart). I took delivery the first week of March 2015. The third was delivered in May.

rectifyer2000

So have any of you guys tried to bypass the NPP to get sound in all modes?

RoketRdr

Well that's some good news. I assume the three of you had cars produced later in the cycle? Someone with a 2016 A8 needs to take a look see and report back.

Off topic: who makes your wheels and what is the color called?

RoketRdr

Its not the NPP that's the problem. You can tune them to stay open at all times in the settings menu. Its the AFM valves that close in V4 mode at low traffic speeds having the same effect as the NPP valves closing.

foreverfuelie

I can't speak for the others, and have never asked, but for me, I enjoy the dual mode system as is. I like "sneaking" out of my neighborhood in the early morning hours and long cruises on the highway in "stealth" or quiet mode. When I want to make noise, it's just a 1/4 turn of the **** away. I don't find the ride too harsh or stiff in sport mode and spend most of the time driving in manual/sport (loud) when I'm out and about and especially around at the races and car shows.

foreverfuelie

My wheels are Finspeed F5-Spyder ultra-lights, in the stock sizes and coated then hand brushed in what Daniel at Finspeed calls "Gronze" for the color. Search the "Finspeed build thread" here on the forum to see them go through the process.

rectifyer2000

So here we go again - another twist that reports the A8 does have control over the NPP function. I've heard the A8 does NOT give you the option to control the NPP but the M7 does. That's why I started this thread, so I can get a well defined answer on the difference between the AFM and NPP, as they apply specifically to the A8, and what control we have over these two sets of valves that have an effect on the sound of the exhaust.

My understanding right now is that the AFM valves will close in V4, regardless of settings, leaving your exhaust quiet, BUT, some newer cars may not have AFM valves? So what's happening with these cars in V4 mode and, what settings are available to them?

I've also read the NPP function can't be controlled in the A8, only the A7....But now I'm hearing again that it can - Hahaha, I don't even have the car yet and I just want to rip out this convoluted muffler system, beat it with a bat and install something less confusing that sounds good - all the time. This system is like an Italian firing squad. I guess I'll just have to wait and see what I get when the car arrives. Maybe by then it will have a Ford Pinto exhaust.