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Nov 12, 2017 | 11:26 AM

#21

bjones7131

Safety Car

Joined: Jan 2014

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From: Walhalla South Carolina

That's because as others said it never goes into 4 cylinder mode unless you have selected the ECO mode of driving. That should be the way the A8 is but it isn't. You have it for sure, it is part of the design.

Nov 12, 2017 | 11:43 AM

#22

Track

Thread Starter

Burning Brakes

Joined: Nov 2017

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I think I’m wrapping myself up. So all cars have AFM, but the newer Z06 doesn’t have the exhaust AFM valves. Rather it is using the sound management valves to add back pressure and control the 4 cylinder tone??

Nov 12, 2017 | 11:52 AM

#23

OnPoint

The Consigliere

Joined: May 2006

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From: 2023 Z06 & 2010 ZR1

Quote:

Originally Posted by Track

Yes. All C7 Corvettes have AFM (Active Fuel Management) - i.e. the ability to operate the engine in V4 mode. The Z06s don't have what are called AFM exhaust valves in the exhaust system. The Z06 relies on the NPP valves in the mufflers to attenuate sound when operated in V4 mode.

All the rest of the Corvette models have AFM exhaust valves in the exhaust system. Some of those Corvettes will have NPP muffler valves if they have the optional sport/performance exhaust option (all the Z06s have NPP exhaust).

All M7 Corvettes will only operate in V4 mode - i.e. AFM actually engaged, when the driver selects Eco mode on the car, and when driving conditions fall within certain parameters. All automatic transmission C7s can operate in V4/AFM mode in any driver mode (again, within certain parameters), unless driven with the paddle-shifters in manual shift mode.

None of the above discussion describes anything to do with the exhaust and intake valves IN THE ENGINE that are used to perform the V4 function via their shutdown and closure.

So - don't feel bad, several terms involved that sound a lot alike (especially valves) but in the end it's fairly straight-forward once you get used to the acronyms.

Last edited by OnPoint; Nov 12, 2017 at 11:55 AM.

Nov 12, 2017 | 11:55 AM

#24

eboggs_jkvl

Moderator emeritus

Joined: Jun 2001

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From: Jacksonville Florida BWO Dayton, Cincinnati, Bloomsbury NJ, Cincinnati

2015 C7 of the Year Finalist

Quote:

Originally Posted by Track

Z06s don't have the AFM exhaust valves because GM can't get the valves to hold up to the heat in the exhaust. Since the plan is for more spirited driving or racing in the Z06, they took off the exhaust valves so they wouldn't fail. If you race the cars, you'll kill the AFM exhaust valves.

Elmer

Nov 13, 2017 | 12:34 AM

#25

Track

Thread Starter

Burning Brakes

Joined: Nov 2017

Posts: 800

Likes: 326

OK, I think I understand now. Thanks for the patient responses!

Nov 13, 2017 | 07:46 AM

#26

JerryU

E-Ray, 3LZ, ZER, LIFT

Joined: Sep 2007

Posts: 35,009

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From: NE South Carolina

Quote:

Originally Posted by bjones7131

I forget what it stands for but it is the performance exhaust baffles that adds 5 hp, it is the two baffles at the exhaust tips.

Quote:

Originally Posted by Track

Well...maybe my AFM engagement feels seamless because I don't have it. I bought the 2017 M7 slightly used, so I still do not know the exact options. I need to get a dealer to print my option list.

That "performance" option is called NPP has nothing to do with 8 to 4 cylinder operation or the AFM valves. It is another set of valves that are on the outer two large exhaust pipes/tips on the muffler. You can see the valves by looking under the rear. (You can see the AFM valves as well as they are before the muffler but you have to crawl under a bit.) Unlike the AFM valves, the NPP valves are either full open or closed.

You might not be able to detect the difference in tip size as you don't have a comparison. But NPP tips fill the opening, the standard smaller tips do not. You'll also see that the outer two exhaust tips become black. I have to clean mine every few hundred miles. Easy to do!

Here is a pic that shows what mine look like. The same as on my 2014 as my current Grand Sport. By the way most paid the ~$1100 where it was an option for the sound, NOT the 5 hp!