Got a new C8 and while driving, I noticed a small V8 / V4 changing (by the speedo). I would hope whatever is controlling this can be turned off as I don't want my car changing into V4 'economy' mode. Not even sure what to look for in the manual, so I'm here... Ideas on how to disable? Thx in advance!

 

You can pay big bucks, get a tune to turn it off, and lose your warranty.
Or, you can drive it in manual mode, drive in Track mode, or in Z mode with powertrain set to Track mode.

 

I set mine to sport mode with Z mode on. This keeps it from changing to V4. I do have to manually upshift one gear to lower the RPM's to around 2000 when cruising on the freeway.

 

Geez, I can't believe one can't disable the shutting down cylinders. Far be it from me to second-guess the Chevy engineers, but is that any good for the engine? Man, I find this weird.

 

It's called Active Fuel Management and you'll find it on page 188 of the 2025 owner's manual.

 

 

I wish this were true in my 2023. Transmission in sport mode still goes to V4 AFM.

 

This should prevent the V4 mode from happening

 

Most of us don't give it a second thought....

 

I don't understand why a person would want to turn it off permanently. It goes into and out of V4 mode seamlessly, the only indication being a light on the dash. What's wrong with getting better fuel economy if there is no lack of power when it's wanted? In it's 6 year production run I don't recall it causing issues even once tho some people report hearing it engage or disengage, and some have said they can sometimes feel it tho those reports have been rare.

I have seen people (on the forum) who want it off during break in, for no reason other than they THINK it may not break in the engine as well, without any evidence to back up those FEELINGS.

But then again, it's their car to do with as they wish. I can respect that even without understanding it.

 

It sounds like crap is the main reason IMO.

 

just drive the car and forget about it. Chevy has got this down pretty well, I can’t tell a damn bit of difference when it shifts from v4 to v8….

 

I want nothing to do with a V4/8 engine mode, but this is where we are at with the latest generation of Corvettes

 

I drive 90% of the time in manual mode and only use D when highway/interstate driving on trips, really do not feel much difference in V4 and probably would not even know except for the indication on the dash?

 

I dont see the V4/V8 mode even making a difference on my ERAY. My MPG is always 10 or 11. Too much city driving and get away from red lights a little aggressive.

The ERAY with the autostop button shutoff is the best feature too. No need to always run Sport or Track that way.

 

10-11mpg is Z06 territory. I'm getting around 20mpg city driving and 25 or so highway on my Eray. You must have a lead foot.
I agree about the Autostip button - except when I forget to push it on startup.

 

In either V8 or V4 mode, when cruising at steady speed (say 60 mph) on flat road (which is basically the only time AFM activates) the mighty V8 engine is producing a whopping 40 hp - and the throttle plate position severely restricts the intake air flow. 5 hp per cylinder in V8 mode. AFM closes both the intake and exhaust valves on 4 cylinders - capturing a combustion charge as it does that - and those cylinders behave as springs with very, very little loss. The remaining 4 cylinders must now produce a whopping 10 hp instead of 5 hp. The throttle plate actually opens just a bit to compensate - and this slightly reduces the intake air flow restriction - or - pumping loss. This results in improved "volumetric efficiency" for the 4 active cylinders, which can produce the needed 40 hp more efficiently than the 8 did. One could view this as crippling the engine, but that view is at odds with the fact that its actually more efficient, in this low power scenario.

I have no issue with it during steady highway cruising. But for back road leisurely driving, it will switch in and out of AFM frequently on small hills, curves, etc., and I can detect it. To avoid it, I use M shift mode. And, I prefer my gear selections anyway in that situation - I don't downshift as soon as the automatic modes would.


clip from a statement by Tadge about AFM:
"Our AFM system is very effective on the small block V8. It lets us close the valves on the de-activated cylinders so the cylinders act as air springs. When the engine rotates we get energy back as the compressed air in the cylinder expands. Other manufacturers just stop fueling the de-activated cylinders and so don't get much fuel savings. The reason 4-cylinder operation is more efficient is that the active cylinders are worked harder with a greater throttle opening. "

 

Never gave it a thought. Had it on my C7. Only difference is indicator light. My guess is vast majority of drivers would never have noticed without the light on the dash.

 

It sucks that they put this in the C7 and now C8. Just charge the extra $$$ per car for the penalty id have been fine with it and I'm sure the rest of you would also.

That afm is such a crap system it's not if but when it causes problems. And to think they put that on the C7 Z06 engines? Junk. But here we are.

 

As a new C8 owner I have a question related to our AFM system. Is this the same system that the full-size SUV's & pickup trucks use when equipped with the 6.2 V8's? I know the NTSB is looking at the rod bearing failures. I also read that there is an issue with the lifters that deactivate the cylinders having roller failure. They freeze, break apart and the fragments eventually cause bottom end failure. Does anyone know for sure what is causing the failures, and should C8 equipped 6.2 V8's be on the lookout for similar issues?
Thanks in advance!

Tom