I've swapped around several aftermarket exhausts but none with AFM valves. Today I put on a Corsa Extreme no mufflers but with AFM valves. In the first few minutes it was obvious how much quieter it was at highway speed yet rowdy when accelerating. I would say highway speed the same as the stock Z51 exhaust. The Corsa valves had slightly larger holes in the flappers than the stock Z51 exhaust. The V4 mode was less noticable with the Corsa and I wonder if it has something to do with the hole size. This made me wonder about the AFM valves operation so I data logged it. They don't only close in V4 mode. They close on deceleration and steady throttle in V8 mode. I always assumed probably like everyone else that they were V4 mode only but they are definitely being used for sound control overall.

 

I never assumed anything about how they work. I just go by what the Service Manual says. It is a description for techs so its not necessarily complete in all the exact details, but yes of course, the primary function is just sound quality. Also there is some hysteresis it says, so once they close the stick closed until engine torque reaches a certain threshold. Probably lots of little details.

"Cylinder Deactivation Exhaust Flow Control Valve System
As a means to improve fuel economy, the engine management systems in some vehicle applications include provisions to deactivate half of the engine cylinders under certain operating conditions. For example, under a light load. The cylinder deactivation exhaust flow control valve subsystem is used to mitigate the impact that powertrain engine cylinder deactivation (active fuel management) has on the quality of the exhaust sound. When the active fuel management system is in operation, the cylinder deactivation exhaust flow control valve subsystem takes over control of the exhaust tailpipe flow control system. When active fuel management is operating, the exhaust tailpipe flow control valves are commanded shut resulting in a quieter exhaust note until the active fuel management system deactivates with increased throttle demand at which time the exhaust tailpipe flow control returns to the operational status determined by the vehicle specific mode that is being used. The cylinder deactivation exhaust flow control system controls the undesirable exhaust noise generated during the cylinder deactivation process. This is achieved through the use of up to two electronically actuated cylinder deactivation exhaust flow control valves in the vehicle exhaust system. The cylinder deactivation exhaust flow control valves are commanded to the closed position by a pulse width modulated signal from the chassis control module in response to active or pending engine cylinder deactivation. When the cylinder deactivation exhaust flow control valves are in the closed position, the engine exhaust flows through a hole machined in the plates integral to the valves. When the engine is operating on all cylinders, the cylinder deactivation exhaust flow control valves are commanded to the open position in order to minimize exhaust restriction. To provide some control hysteresis, once the cylinder deactivation exhaust flow control valves have been commanded to the closed position, they are not reopened until the engine torque reaches a calibrated minimum value that is determined as a function of the driver selectable performance mode."

 

My point was that they are closed alot more than just in V4 mode. One thing I forgot to note is they always were closed for a short timeframe before V4 mode.

 

I see. The description does say "The cylinder deactivation exhaust flow control valves are commanded to the closed position by a pulse width modulated signal from the chassis control module in response to active or pending engine cylinder deactivation," which would imply they com on before the cylinders are deactivated.

From the hysteresis statement, it looks like if it was in V4 mode and exited that mode because of coasting, even though it has returned to V8 mode, those valve may stay shut until some engine torque is evident ( I don't know how it detects that}.

It does not describe any cases where they close that are un-related to V4 mode, if that is what you are finding. But, as noted, the description do not necessarily contain all the cases and details.

 

Hello sir…..so I believe you just installed the corsa I am interested in?!?!
can’t find any reviews.
can you tell me the part number and your thoughts on it?
I want to retain my npp but wanna have it fairly quiet when I close the valves but was worried since no mufflers I wouldn’t like it.???
thx man

 

I would say definitely the low torque scenario it makes sense.

 

I installed the 21102blk this doesn't have NPP or mufflers. Look on the Corsa site they have it with NPP and mufflers.

 

Have you noticed, do they ever close while the tailpipe flow control valves are stay open?

 

That's a good point I didn't have that on the stream. I'll do that next time just to see.

 

Good info! Thank you for sharing.

 

Just so you're tracking, there is no Corsa system offered with no mufflers that has NPP valves. You can get AFM valves with no mufflers but if you want to retain NPP functionality, you have to opt for their system with mufflers. The specs say it is marginally quieter than stock in tour and +9 dB louder in rowdy modes.

 

I don't see the point but yes they do.

 

Forces the exhaust path through smaller diameter outlet pipes to marginally tone down the volume.

MagnaFlow offers something similar to control volume & drone, as well:

 

Yup - its an option under npp - muffler delete. I suppose it provides a place to mount the tailpipe flow control valves if you dont want a mufller - and don't want to buy simulators?

 

Like I said……..all valves used……No mufflers

 

Once I get bored with this one I might check with Corsa on buying just the NPP valve piece. Thinking about it now it probably does change it quite a bit pushing it through just two 2.5" pipes vs two 3" and two 2.5" overall though I'm very impressed with the Corsa setup I bought.

 

Weird. When I go on their site and Select "2023>Chevrolet>Corvette>Coupe w/ NPP" I do not get any system with 4 valves and no mufflers. I stand corrected but I still don't think it is going to do much changing of the sound with no mufflers.

 

Yea…….they don’t always show it,you gotta kinda look for it.
And yea I kinda agree it may not be much difference between open and closed but really would like to know.
if it does quite up enough I think I’d really like it cuz open would be LOUD!!!😁

 

I looked down the page and it give options. Select muffler delete and it shows you version with valves but no muffler. My thought is, its for those with NPP that do not want mufflers - but it provides a place to mount the valve actuators so you do not need simulators to avoid setting a code.

 

Any more testing? Do the AFM valves ever close in tour+manual mode? What other combinations of AFM/NPP actuations were observed?