C8 AFM Disable?
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
I call out lack of sense, logic, ignorance, whatever you want to call it. I've actually seen people post "I don't want it because I BOUGHT a V8 and by God that's what I want." This statement shows a 100% lack of understanding. It ONLY works while the car is at steady state cruise with zero acceleration. The driver wouldn't know if it had an engine or if it was being towed by a Schnauzer. Yet they act as if this wheezing 4 cylinder just won't snap out of it as traffic leaves them in the dust as they desperately attempt to accelerate. It is NOT the case in the remotest way. My sky is just fine, I'm just trying to ask the uninformed to open their minds a bit and learn.
lol...irony is thick...
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
That poster acknowledged it was an imperfect test - but it's more evidence than your "I don't believe it saves gas" evidence.
For real though...
I do agree the problem is minimal with the c8 on the afm but its not that great on other GM engines.......but I'm sticking you can't verify a real fuel savings and cost add justification on any of them...but its ok...you like grape kool aide its all good...
For real though...
I do agree the problem is minimal with the c8 on the afm but its not that great on other GM engines.......but I'm sticking you can't verify a real fuel savings and cost add justification on any of them...but its ok...you like grape kool aide its all good...
^^^
This. GM didn't spend tens or hundreds of millions developing the technology, and further millions buying millions of complex parts, because it doesn't work. How big a gain is going to be dependent on a lot of factors, many related to the driver, but especially on the highway the benefits are real.[/QUOTE]
^
Link to where they spend hundreds of millions of dollars on that crappy AFM design..
They need a refund..
and for the record my evidence is my actual test...I tried a month never using it and a month using it normally and there was zero difference using very close to the same mileage and routes and drving and gas station down to the same pump... C7a few years ago...Internet is full of peeps that have defeated them with no apparent change in efficiency before and after MPG...very tiny gain of any...< 1mpg imo regardless...
Its evident have not kept up with the history of GM **** ups...the list is long....
I'm out though...Here is to hoping your car never eats itself because of AFM failing...
Last edited by hawkgfr; Jun 13, 2025 at 01:14 PM.
Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,528
Why would a collapsed lifter (or non collapsing lifter) cause it to get stuck in the bore? That's not remotely logical. Nothing is putting a sideways load on the lifter in that case. If the lifter stays in the normal position, there's no more wear on the lifter or pushrod than when in V8 mode - the lifter is doing what it's designed to do: translate the motion of the pushrod to open the valve. If it fails in the collapsed mode, it seems to me it's putting even less wear on the pushrod, as it (the pushrod) is must moving up and down with virtually no resistance. In either case it's not optimum and will cause drivability issues, but I don't see a path for serious damage.
I still don't see any valid cause for the "extreme engine damage" or "destroyed engine" that people claim from failures of the system.
I agree that hydraulic lifters do fail, rarely. And that's been true long before anyone at GM even dreamed of AFM. Had it happen on my dad's 66 Dodge. I agree with the statement that people who have a lifter failure, and often any other top end issues, like to blame it on AFM. I talked to one Chevy dealership mechanic who said lifter failures happen about the same amount on regular and AFM lifters.
I still don't see any valid cause for the "extreme engine damage" or "destroyed engine" that people claim from failures of the system.
I agree that hydraulic lifters do fail, rarely. And that's been true long before anyone at GM even dreamed of AFM. Had it happen on my dad's 66 Dodge. I agree with the statement that people who have a lifter failure, and often any other top end issues, like to blame it on AFM. I talked to one Chevy dealership mechanic who said lifter failures happen about the same amount on regular and AFM lifters.
Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,528
Sure, GM designed it over a weekend with a couple of guys with pizza and beer. LOL, how to say you understand nothing about engineering and design in the auto industry.
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
I have to laugh at how you couldn't answer post # 434 so you ignored it. BTW, there is no irony in what I posted. There were two things that slowed me down from ordering my 2020 SR, the DCT and the AFM. Both of which, when I opened my mind and gave them a chance to be tried, turned out to be fantastic. There are a lot of dinosaurs that just refuse to accept change and with hands on hips declare it to be bad without even trying it. At one car show I had some pot bellied old loser look at my car and with an ugly sneer and crossed arms that said "Nope, engines in the wrong place." I said, "you better tell GM, they're the ones who made it."
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
Exactly, it would take a LOT of effort just for the programming, testing, and verification of the software, much less the engineering of the hardware. They time it so the shut off cylinders act as air springs, the timing of this alone is significant. Those who trivialize things like this simply prove to the world their lack of understanding.
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
I have to laugh at how you couldn't answer post # 434 so you ignored it. BTW, there is no irony in what I posted. There were two things that slowed me down from ordering my 2020 SR, the DCT and the AFM. Both of which, when I opened my mind and gave them a chance to be tried, turned out to be fantastic. There are a lot of dinosaurs that just refuse to accept change and with hands on hips declare it to be bad without even trying it. At one car show I had some pot bellied old loser look at my car and with an ugly sneer and crossed arms that said "Nope, engines in the wrong place." I said, "you better tell GM, they're the ones who made it."
Metric **** ton of irony that you say there is no irony....The answer to post 434 was not ignored lol...the answer obvious...the same exact reason they put auto stop start....EPA bowing to climate whataboutism and mandating idiocy....but hey you don't see irony either so I shouldn't be surprised you didn't know...
You win...
Hopefully yours don't puke as well....
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Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
Metric **** ton of irony that you say there is no irony....The answer to post 434 was not ignored lol...the answer obvious...the same exact reason they put auto stop start....EPA bowing to climate whataboutism and mandating idiocy....but hey you don't see irony either so I shouldn't be surprised you didn't know...
Race Director
Joined: Aug 2016
Posts: 12,812
Likes: 10,229
From: Garden Valley CA
Why would a collapsed lifter (or non collapsing lifter) cause it to get stuck in the bore? That's not remotely logical. Nothing is putting a sideways load on the lifter in that case. If the lifter stays in the normal position, there's no more wear on the lifter or pushrod than when in V8 mode - the lifter is doing what it's designed to do: translate the motion of the pushrod to open the valve. If it fails in the collapsed mode, it seems to me it's putting even less wear on the pushrod, as it (the pushrod) is must moving up and down with virtually no resistance. In either case it's not optimum and will cause drivability issues, but I don't see a path for serious damage.
I still don't see any valid cause for the "extreme engine damage" or "destroyed engine" that people claim from failures of the system.
I agree that hydraulic lifters do fail, rarely. And that's been true long before anyone at GM even dreamed of AFM. Had it happen on my dad's 66 Dodge. I agree with the statement that people who have a lifter failure, and often any other top end issues, like to blame it on AFM. I talked to one Chevy dealership mechanic who said lifter failures happen about the same amount on regular and AFM lifters.
I still don't see any valid cause for the "extreme engine damage" or "destroyed engine" that people claim from failures of the system.
I agree that hydraulic lifters do fail, rarely. And that's been true long before anyone at GM even dreamed of AFM. Had it happen on my dad's 66 Dodge. I agree with the statement that people who have a lifter failure, and often any other top end issues, like to blame it on AFM. I talked to one Chevy dealership mechanic who said lifter failures happen about the same amount on regular and AFM lifters.
Don't get me wrong, there isn't any evidence that the LT engine AFM lifters fail at a significantly higher rate than non AFM-lifters, nor not using the system once installed prevents its failure.
Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,528
Metric **** ton of irony that you say there is no irony....The answer to post 434 was not ignored lol...the answer obvious...the same exact reason they put auto stop start....EPA bowing to climate whataboutism and mandating idiocy....but hey you don't see irony either so I shouldn't be surprised you didn't know...
You win... Hopefully yours don't puke as well....
You win...
Hopefully yours don't puke as well....
Race Director
Joined: Mar 2007
Posts: 11,425
Likes: 8,576
It gets stuck in the bore when people drive long enough with a failed lifter to cause other problems (generated contamination, extreme wear, etc.) to jam it or when the engagement pin fails to the point where it exits the lifter and jams in the bore. Here is a good video explaining how the lifter fails:
https://www.youtube.com/watch?v=gEcxI2nwwxE
Don't get me wrong, there isn't any evidence that the LT engine AFM lifters fail at a significantly higher rate than non AFM-lifters, nor not using the system once installed prevents its failure.
https://www.youtube.com/watch?v=gEcxI2nwwxE
Don't get me wrong, there isn't any evidence that the LT engine AFM lifters fail at a significantly higher rate than non AFM-lifters, nor not using the system once installed prevents its failure.
I knew that oil pressure controlled the lifter collapse event, but I did not know that pressure causes it to collapse, absence of pressure causes it to lock (not collapse). Again, it seems like if its never activated - it would just remain locked.
Just asking.
Race Director
Joined: Aug 2016
Posts: 12,812
Likes: 10,229
From: Garden Valley CA
So no operational evidence. But doesn't this seem to make the case that preventing AFM activation may actually prevent a failure? Right about 4:48 he says that mis-timed switching event, you "can really beat up the camshaft". Disable AFM and no switching events. It been said several times that there is no evidence that disabling it prevents failure. But maybe it does after all?
I knew that oil pressure controlled the lifter collapse event, but I did not know that pressure causes it to collapse, absence of pressure causes it to lock (not collapse). Again, it seems like if its never activated - it would just remain locked.
Just asking.
I knew that oil pressure controlled the lifter collapse event, but I did not know that pressure causes it to collapse, absence of pressure causes it to lock (not collapse). Again, it seems like if its never activated - it would just remain locked.
Just asking.
Safety Car
Joined: Nov 2005
Posts: 4,381
Likes: 939
From: Huntsville Alabama
Got my 2022 back. Tested the Carbite. It does work after 165. 167 when it starts and V8 all the time (165 still has V4).
But one thing I am trying to figure out at first, I swear there was some rough running when loading a Gear in manual mode. So say 1500 rpms in 7th, and give it heavy throttle to load accel some without down shifting. If I remove Carbith it pulls smooth, with installed I can feel some non smoothness.... at least I think... more testing but welcome someone else seeing if they notice it or maybe it was just me getting use to the car after not having it for a few weeks. Also car was learning trans so maybe it was related, maybe the gas after sitting for 4-5 weeks for new trans was not up to the task of that load.. More testing but it works on 2022.
I will say when the car wants to swap to V4, it never does BUT the AFM valves shut and then open. I have a track exhaust with AFM valves so you can tell when it flicks shut and then back open.
But one thing I am trying to figure out at first, I swear there was some rough running when loading a Gear in manual mode. So say 1500 rpms in 7th, and give it heavy throttle to load accel some without down shifting. If I remove Carbith it pulls smooth, with installed I can feel some non smoothness.... at least I think... more testing but welcome someone else seeing if they notice it or maybe it was just me getting use to the car after not having it for a few weeks. Also car was learning trans so maybe it was related, maybe the gas after sitting for 4-5 weeks for new trans was not up to the task of that load.. More testing but it works on 2022.
I will say when the car wants to swap to V4, it never does BUT the AFM valves shut and then open. I have a track exhaust with AFM valves so you can tell when it flicks shut and then back open.
Race Director
Joined: Mar 2007
Posts: 11,425
Likes: 8,576
Got my 2022 back. Tested the Carbite. It does work after 165. 167 when it starts and V8 all the time (165 still has V4).
But one thing I am trying to figure out at first, I swear there was some rough running when loading a Gear in manual mode. So say 1500 rpms in 7th, and give it heavy throttle to load accel some without down shifting. If I remove Carbith it pulls smooth, with installed I can feel some non smoothness.... at least I think... more testing but welcome someone else seeing if they notice it or maybe it was just me getting use to the car after not having it for a few weeks. Also car was learning trans so maybe it was related, maybe the gas after sitting for 4-5 weeks for new trans was not up to the task of that load.. More testing but it works on 2022.
I will say when the car wants to swap to V4, it never does BUT the AFM valves shut and then open. I have a track exhaust with AFM valves so you can tell when it flicks shut and then back open.
But one thing I am trying to figure out at first, I swear there was some rough running when loading a Gear in manual mode. So say 1500 rpms in 7th, and give it heavy throttle to load accel some without down shifting. If I remove Carbith it pulls smooth, with installed I can feel some non smoothness.... at least I think... more testing but welcome someone else seeing if they notice it or maybe it was just me getting use to the car after not having it for a few weeks. Also car was learning trans so maybe it was related, maybe the gas after sitting for 4-5 weeks for new trans was not up to the task of that load.. More testing but it works on 2022.
I will say when the car wants to swap to V4, it never does BUT the AFM valves shut and then open. I have a track exhaust with AFM valves so you can tell when it flicks shut and then back open.
"The new dual-clutch transmission, however, has less inherent capability
to mask engine vibration, which is why cylinder-deactivation technology
has so rarely been used on a car with a dual-clutch transmission. The C8
engineers were able to marry these two technologies in the new Corvette,
however, by putting some micro-slip into the clutch control of the DCT.
As a result, those transitions are almost imperceptible, or as Kociba claims
“butter-smooth.”
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 35,019
Likes: 12,401
From: NE South Carolina
This is most interesting! Its too bad we don't know exactly how the CarByte works. But your experience suggests that while it prevents the lifter collapse, it does not prevent the closing of the AFM exhaust flow control valves. I wonder what else it does not prevent. As noted from the MidEngine Revolution book, there is some clutch micro-slip to mask engine vibration when AFM is active. I wonder if the non-smoothness you feel is because that feature is also not prevented (just speculation). Here is the statement about micro-slip:
.....
.....
All exhaust passing thru those small holes has to incorporated with the small clutch slip Tadge Juechter said occurs with the V8/V4 transition (when all is working properly.)
Drifting
Joined: Aug 2022
Posts: 1,903
Likes: 791
From: Stamford, CT
I am loving the non-AFM driving
Got my 2022 back. Tested the Carbite. It does work after 165. 167 when it starts and V8 all the time (165 still has V4).
But one thing I am trying to figure out at first, I swear there was some rough running when loading a Gear in manual mode. So say 1500 rpms in 7th, and give it heavy throttle to load accel some without down shifting. If I remove Carbith it pulls smooth, with installed I can feel some non smoothness.... at least I think... more testing but welcome someone else seeing if they notice it or maybe it was just me getting use to the car after not having it for a few weeks. Also car was learning trans so maybe it was related, maybe the gas after sitting for 4-5 weeks for new trans was not up to the task of that load.. More testing but it works on 2022.
I will say when the car wants to swap to V4, it never does BUT the AFM valves shut and then open. I have a track exhaust with AFM valves so you can tell when it flicks shut and then back open.
But one thing I am trying to figure out at first, I swear there was some rough running when loading a Gear in manual mode. So say 1500 rpms in 7th, and give it heavy throttle to load accel some without down shifting. If I remove Carbith it pulls smooth, with installed I can feel some non smoothness.... at least I think... more testing but welcome someone else seeing if they notice it or maybe it was just me getting use to the car after not having it for a few weeks. Also car was learning trans so maybe it was related, maybe the gas after sitting for 4-5 weeks for new trans was not up to the task of that load.. More testing but it works on 2022.
I will say when the car wants to swap to V4, it never does BUT the AFM valves shut and then open. I have a track exhaust with AFM valves so you can tell when it flicks shut and then back open.
Safety Car
Joined: Nov 2005
Posts: 4,381
Likes: 939
From: Huntsville Alabama
No maybe I typed that wrong or maybe you both read it wrong.
Let me clarify.
The AMF valve you can hear shut and instantly open. Probably does not even close all the way. I just happen to have loud track exhaust so when V4 would normal change over, I can hear the AFM valve change the note for a split second... then its back loud. This has NOTHING to do with the smoothness I was asking about. The car not switching in and out of V4 in auto mode around town is much smoother in that aspect, no changin in and out and has V8 even when lugging it around and pulls small kills with out it kicking in and out of V4/V8.
The smoothness that I questioned was in MANUAL mode. so V4 was not active anyway. You can not load a gear in auto mode it will down shift as engine load increases.
So in Manual mode, 7th gear 1500 rpms. load the motor heave with accelerator, THIS is when I felt the motor was not as smooth as normal. But maybe it was older fuel, maybe it was just the hew trans, the roads, I don't know. Most testing will be needed. But figured I would ask since there is a thread of people playing with the same part.
Let me clarify.
The AMF valve you can hear shut and instantly open. Probably does not even close all the way. I just happen to have loud track exhaust so when V4 would normal change over, I can hear the AFM valve change the note for a split second... then its back loud. This has NOTHING to do with the smoothness I was asking about. The car not switching in and out of V4 in auto mode around town is much smoother in that aspect, no changin in and out and has V8 even when lugging it around and pulls small kills with out it kicking in and out of V4/V8.
The smoothness that I questioned was in MANUAL mode. so V4 was not active anyway. You can not load a gear in auto mode it will down shift as engine load increases.
So in Manual mode, 7th gear 1500 rpms. load the motor heave with accelerator, THIS is when I felt the motor was not as smooth as normal. But maybe it was older fuel, maybe it was just the hew trans, the roads, I don't know. Most testing will be needed. But figured I would ask since there is a thread of people playing with the same part.