C8 AFM Disable?
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 35,024
Likes: 12,406
From: NE South Carolina
Thanks for the clarification my car should be built this week (fingers crossed I have a TPW of 4/8) so can't wait and trying to learn as much as I can. My Raptor doesn't have AFM but does have start stop which I disable permanently with Forscan. Someone needs to develop GMScan lol.
Good reading while you wait. Note, it's not your father's "slushbox!"
I made a summary of the DCT features some years ago. Mostly includes statements from GM’s DCT Controls Manager, a C8 forum post by Tadge and comments about "boosted shift" made by a GM engineer Ed Piatek. Pretty impressive options.
- The C8 DCT transmission has different automatic shift strategies for the various drive modes, which adapt in real time. The more aggressive, the more spirited you drive, the more aggressive the car's responds, -start to relax, the car starts to relax.
- The DCT uses latitudinal and longitudinal accelerometers, and looks at information like throttle position and steering angle to gauge how the car is being driven, and react accordingly. In Track mode set to automatic, the car will downshift aggressively when the driver is braking hard into a corner, and hold upshifts until corner exit. (PS: I love the aggressive downshifts thru several gears, Rev Matching each all in the blink of a eye. Use often when I leave the 4-lane divided highway with traffic going ~70 mph and I turn on our 25 mph limit rural road in the CC where I live. I call it Rev Match Music!)
- The C8 has two manual modes. If you pull a paddle while in Drive, you get a temporary manual mode, which automatically times out, or can be exited sooner by holding the upshift paddle. In this mode, the car will automatically upshift at redline. If you press the M button in the center console, you get full manual mode. There's no time out, and the car won't upshift at redline.
- Hold the downshift paddle, the DCT will serve up the lowest possible gear. Do that while braking, and the transmission will keep downshifting as engine speed allows.
- Pulling both paddles at the same time is equivalent to pushing in the clutch pedal on a manual car, which allows you to rev the C8's new V-8 as much as you want.
- The paddles are directly wired to the transmission control module (TCM) for quicker response times. This doesn't mean the paddles will give you a downshift that over-revs the engine—the TCM prevents that.
- With the C8's Performance Launch mode, the car uses the inertia of the engine coming down between revs to propel the car forward. Frankl, GM has not provided many details on this feature. This is more info by GM’s Engineer Ed Piatek: “We found that during very aggressive launches we can drive torque through both shafts/clutches simultaneously which improves the 0 to 60 times.” Road and Track interpretation of that statement was: "With the C8's Performance Launch mode, the car will actually use the inertia of the engine coming down between revs to propel the car forward. Chevy calls these "Boosted Shifts," and they're only used with a Performance Launch."
- You can avoid V4 mode using the “M” manual button or temporally for 5 seconds after pulling the last shift paddle. The new "Z" mode comes from the factory set up as an extra sporty mode including shift schedules pulled from the "Track" mode, so that will be V8 only. You can customize "Z" mode any way you want, so if you elect another shift pattern, V4 mode will return.
- I follow what a poster recommended as it’s like a different car! I drive in Z MODE with Power set to Track. If you have MRC you can set ride to Touring and get a softer ride. Can set Steering, eBoost and NPP where you would like. It upshifts and downshifts at higher rpm. Seldom shifts past 5th gear (have to be at ~72 mph before it will shift to 6th.) Never goes into V4. Can still pull paddles if and when desired.
Last edited by JerryU; Apr 10, 2024 at 01:29 AM.
Instructor
Joined: Nov 2023
Posts: 191
Likes: 120
From: Atlanta area
Pro
Joined: May 2023
Posts: 656
Likes: 311
From: About an hour north west of Albany, NY
AFM in a C8 should be the owners option, without having to change drive modes everytime I start the car. My $.02
"The only way to get rid of AFM all the time is to sell your C8."
As for this comment, not true. You can get your ECM unlocked and a performance tune installed including the elimination of AFM if wanted, but the cost is really steep.
"The only way to get rid of AFM all the time is to sell your C8."
As for this comment, not true. You can get your ECM unlocked and a performance tune installed including the elimination of AFM if wanted, but the cost is really steep.
Instructor
Joined: Nov 2023
Posts: 191
Likes: 120
From: Atlanta area
Drifting
Joined: Nov 2023
Posts: 1,680
Likes: 1,279
Usually I’m fighting the opposite, which is cars set up for max mpg and they upshift as fast as possible and the car just feels lazy…. Never liked cars like that…. A good performance car can turn on the jets when you need it….
I’m still doing break in miles and with the drive train in track the car doesn’t want to shift until I’m several
thousand rpm over the max rpm allowed during break in 🤦♂️….. And I didn’t give it very long to really figure out how to drive with the power train in track but after break in is done I will try again…. Also don’t mind manual mode most of the time…
Regardless… the customer centric answer would be to give owners a disable button just like auto shut off… if these features are that great at saving fuel with no downside most owners will use them. And for those of us who are very particular how our car functions were good too…. It would cost pennies to add an off switch and avoid the hassle of “who’s car is it anyway?”
Moderator
Joined: Feb 2006
Posts: 39,140
Likes: 17,987
From: DFW Area TX
You can use the paddle to upshift whenever you want to lower the revs. I keep mine in Z mode with track shift and I upshift manually when cruising.
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Michael S. Palmer
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 35,024
Likes: 12,406
From: NE South Carolina
^^^
I do the same. Also if I don't have a need to apply the brakes aggressively and have it downshift aggressively, I pull the downshift paddle coming to a turn. But in my rural driving it's unusually just where I dove my two C7s. Never used 7th nor found 6th useful.
I also use MY Mode set to Sport, uses all 8 gears. Funny, the main use for 8th gear other than on an Interstate is for GM to get that last drop out of the EPA mpg test! An OD ratio of 0.33:1 in 8th, even 0.4:1 in 7th is an overkill for normal driving, IMO. Heck 4th is an OD ratio of 0.88:1 and 5th 0.66:1. Typical early automatic trans OD ratios were 0.7:1. Grated with the Dif and intermediate gear, that final ratio is higher (or lower depending how you look at it) than the typical Dif ratio back then. Although my 1st car originally had a small displacement 136 cid flathead V8, with only 60 hp. It needed that 4.56:1 Dif it came with standard to go up hills.
Not far from the Z51 5.17:1.
I do the same. Also if I don't have a need to apply the brakes aggressively and have it downshift aggressively, I pull the downshift paddle coming to a turn. But in my rural driving it's unusually just where I dove my two C7s. Never used 7th nor found 6th useful.
I also use MY Mode set to Sport, uses all 8 gears. Funny, the main use for 8th gear other than on an Interstate is for GM to get that last drop out of the EPA mpg test! An OD ratio of 0.33:1 in 8th, even 0.4:1 in 7th is an overkill for normal driving, IMO. Heck 4th is an OD ratio of 0.88:1 and 5th 0.66:1. Typical early automatic trans OD ratios were 0.7:1. Grated with the Dif and intermediate gear, that final ratio is higher (or lower depending how you look at it) than the typical Dif ratio back then. Although my 1st car originally had a small displacement 136 cid flathead V8, with only 60 hp. It needed that 4.56:1 Dif it came with standard to go up hills.
Not far from the Z51 5.17:1.
Drifting
Joined: Sep 2020
Posts: 1,461
Likes: 1,200
From: DFW
In my AMG turning the auto shut off is part of enabling my “individual” setting so it gets turned off every time I get in the car….
In my wife’s car I have to find the “off” button to disable the feature…. Nothing annoys me more than forgetting and coming to a stop and the engine dying….
But at least I can turn it off…. We can’t turn AFM off… if we can’t buy cars without these “features” we don’t want we should at least be able to turn them off…
I only have a handful of miles on my C8 and already I find myself looking down checking if the V4 light is coming on and trying to drive around it…. According to the manual driving in Sport mode or Z mode with engine in Sport, at least limits AFM to gears 5-8 vs Touring or My mode which allows AFM to activate in gears 4-8….. Track or manual mode is no AFM…. I like driving in manual mode but I wish the car had a normal shift lever. I learned to drive on manual transmission cars and almost always drive with my left hand so my right hand is not usually on the wheel for right paddle upshifts (first world problems…. I know…) but it’s hard to break the habit when you learned to drive that way…
In my wife’s car I have to find the “off” button to disable the feature…. Nothing annoys me more than forgetting and coming to a stop and the engine dying….
But at least I can turn it off…. We can’t turn AFM off… if we can’t buy cars without these “features” we don’t want we should at least be able to turn them off…
I only have a handful of miles on my C8 and already I find myself looking down checking if the V4 light is coming on and trying to drive around it…. According to the manual driving in Sport mode or Z mode with engine in Sport, at least limits AFM to gears 5-8 vs Touring or My mode which allows AFM to activate in gears 4-8….. Track or manual mode is no AFM…. I like driving in manual mode but I wish the car had a normal shift lever. I learned to drive on manual transmission cars and almost always drive with my left hand so my right hand is not usually on the wheel for right paddle upshifts (first world problems…. I know…) but it’s hard to break the habit when you learned to drive that way…
Drifting
Joined: Nov 2023
Posts: 1,680
Likes: 1,279
I’m not particularly worried about it…. It’s just a “feature” I have never experienced before and I’m of the opinion that for a bunch reasons most new cars have more “tech” than we need and in some cases if we had the choice would be happier without…
Race Director
Joined: Mar 2007
Posts: 11,432
Likes: 8,588
I never see the V4 light because I have my display theme defaulted to Track Mode, regardless of the actual drive mode I have selected. I chose that because the Track Mode display theme is the only one that allows 4 info tiles to be selected and displayed. The other display themes only allow two info tiles. Any the V4-8 indicator does not appear with that display theme.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 35,024
Likes: 12,406
From: NE South Carolina
It catches my eye when the V8 and V4 indicator light swaps back and forth….. Usually when something lights up on a dash board the driver is supposed to notice….
I’m not particularly worried about it…. It’s just a “feature” I have never experienced before and I’m of the opinion that for a bunch reasons most new cars have more “tech” than we need and in some cases if we had the choice would be happier without…
I’m not particularly worried about it…. It’s just a “feature” I have never experienced before and I’m of the opinion that for a bunch reasons most new cars have more “tech” than we need and in some cases if we had the choice would be happier without…
I recall the1st Vette I tried to buy in 1974. My Uncle was GM at a very large Chevy dealership in a very big East Coast City. Could not get me one as GM was totally sold out. Total sales that year of 37,500. Two years prior it was only 27,000. And with new EPA emissions requirements the 350 cid small block only had ~200 hp. You had to get the 454 cid BB to get 270 hp!
Just consider, with the exact same bore spacing as I had in my 200 hp, 265 cid1956 Chevy small block the LT2 has 378 cubic inches, 11.5:1 compression, 495 hp with only 93 octane gas. Yep back in the day with a hot-rodded small block at 11:1 compression we had to run 100 octane Sunoco 260. Race gas can have 115+ octane. Nope give GM engineers a lot credit. Without technology can't get there!
Melting Slicks
Joined: Apr 2021
Posts: 2,604
Likes: 2,654
From: Texas
That does work but when I tried that for a few miles for me it was too annoying having the car rev so much just crusing around town.
Usually I’m fighting the opposite, which is cars set up for max mpg and they upshift as fast as possible and the car just feels lazy…. Never liked cars like that…. A good performance car can turn on the jets when you need it….
I’m still doing break in miles and with the drive train in track the car doesn’t want to shift until I’m several
thousand rpm over the max rpm allowed during break in 🤦♂️….. And I didn’t give it very long to really figure out how to drive with the power train in track but after break in is done I will try again…. Also don’t mind manual mode most of the time…
Regardless… the customer centric answer would be to give owners a disable button just like auto shut off… if these features are that great at saving fuel with no downside most owners will use them. And for those of us who are very particular how our car functions were good too…. It would cost pennies to add an off switch and avoid the hassle of “who’s car is it anyway?”
Usually I’m fighting the opposite, which is cars set up for max mpg and they upshift as fast as possible and the car just feels lazy…. Never liked cars like that…. A good performance car can turn on the jets when you need it….
I’m still doing break in miles and with the drive train in track the car doesn’t want to shift until I’m several
thousand rpm over the max rpm allowed during break in 🤦♂️….. And I didn’t give it very long to really figure out how to drive with the power train in track but after break in is done I will try again…. Also don’t mind manual mode most of the time…
Regardless… the customer centric answer would be to give owners a disable button just like auto shut off… if these features are that great at saving fuel with no downside most owners will use them. And for those of us who are very particular how our car functions were good too…. It would cost pennies to add an off switch and avoid the hassle of “who’s car is it anyway?”
Last edited by Korbek; Apr 11, 2024 at 03:04 PM.
1st Gear
Joined: Apr 2024
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Instructor
Joined: Nov 2023
Posts: 191
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From: Atlanta area
Le Mans Master
Joined: Apr 2018
Posts: 5,812
Likes: 8,303
From: Dove Mountain, AZ
2023 C8 of the Year Finalist - Unmodified
With respect to my '23 C8 Z51, AFM has been seamless and undetectable...The only way I know if it's transitioned over to V4 mode is if I see the V4 light illuminated in the DIC...
Last edited by tadda; Apr 12, 2024 at 03:48 PM.
Instructor
Joined: Nov 2023
Posts: 191
Likes: 120
From: Atlanta area
DCT failure around 1%... "Not a big deal, most people don't seem to have issues"
Meanwhile, literally ZERO cases of valve issues due to excess carbon from the PCV system... is "OMG, you have to have a catch can or your motor will blow up"....
Now we can add 4 cyl mode to the mix, I guess? I have yet to hear about an issue from it, although there were bad batches of faulty lifters out there in previous motors, but if they were breaking, it wouldn't matter if the motor was going between 4 and 8 cyl mode... just having lifters that were structurally weak and prone to breaking, was the problem, not the 4 cyl mode....
Advanced
Joined: Oct 2023
Posts: 59
Likes: 36
If anyone has an aftermarket exhaust you know V4 sounds like ****. I like driving in manual mode sometimes but not all the time. I also don't like putting my car into track mode all the time. I just don't want the AFM system to be active. I personally think AFM systems are a joke and the MPG gains are so minimal the benefit isn't enough for me to not want to delete mine. I see a Range Technology disabler in my future. Who is running one and what have your results been? I've heard they work great.
Pro
Joined: Jul 2021
Posts: 694
Likes: 617
From: Crosslake, MN
If anyone has an aftermarket exhaust you know V4 sounds like ****. I like driving in manual mode sometimes but not all the time. I also don't like putting my car into track mode all the time. I just don't want the AFM system to be active. I personally think AFM systems are a joke and the MPG gains are so minimal the benefit isn't enough for me to not want to delete mine. I see a Range Technology disabler in my future. Who is running one and what have your results been? I've heard they work great.