I am concerned about the long term impact of the cylinder deactivation as I plan to own my C8 for many years. So I usually drive in track mode, Z mode, or one of the other modes in manual to keep it from going down to four cylinders.
if I am ripping around town my gas mileage is certainly in the 15-17 mpg range, but put this amazing car on the highway and it is super efficient even at speeds around 80 mph on all eight cylinders. I don’t understand why they force the deactivation on us.

 

To meet gov regs. Why worry. Almost zero reports of any valve issues even though many are paranoid about it. Other vehicles especially Honda do have issues with it.

 

Your console has a "M" on the selector!

 

I had a 1981 Cadillac Seville with 4-6-8 cylinder cutout. Worked great. So 40 years later yesterday is today again. We take a Sunday cruise with some highway miles. I watch the switch to V4 and can't tell the cutout has happened. Seamless. And who hates better mileage?

 

As said above, it is only to help GM meet CAFE standards across the GM line to Federal mandates.

 

Mine switches from 4 to 8 and I never know it or feel it. I am not going to worry about what might happen and just enjoy driving it.

 

It has cylinder deactivation ???

 

Update your profile to let us know what you drive.

 

I can't say that it bothers me. Hopefully they have tested these engines for durability up to several hundred thousand miles.

 

I don't notice the switch either. if my back window is down and I am paying attention I can hear the shift. But my concern stems from what I have seen from doing a little research on Gemini and Grok: "Carbon Buildup: One side benefit of staying in V8 mode rather than V4 is that you keep all the cylinders at a consistent operating temperature. In V4 mode, the "dead" cylinders can occasionally cool down enough to allow for slight oil migration past the rings; keeping all 8 firing keeps everything sealed and clean." Not sure how impactful this is as sometimes AI make bigger deal out of something than it really is

 

The current administration has removed penalties for not meeting CAFE mileage requirements. So it's a regulation with no teeth.

 

There does not appear to be any evidence to support that the LT2 engine has any issue with chronic failures specifically related to the cylinder deactivation. There are a few lifter failures but they are not frequently reported and are not consistently the 8 AFM lifters. And there is also no evidence that avoiding V4 mode will prevent a failure if one is going to occur. In other words, if there is defect that is going to lead to an eventual lifter failure, there is no evidence that avoiding V4 stops it - and frankly would you want to?

There were AFM lifter failures in other GM engines so that is concern for many.

Some think it might shorten engine life because 4 cylinders being shut down. Perhaps uneven heating or something. The V4 does have a timeout feature so after a while it switches to V8. Its might be for thermal concerns, but then again it might be for another reason. They shut down each cylinder just before combustion, the cylinder fires, and it captures a combustion charge. After a period of time it that leaks down - so it could be for that reason. But I don't know-that is just a guess. The other thing is V4 only kicks in at very low power demand - the throttle plate is barely cracked- the engine is severely restricted - the manifold vacuum is high - and each cylinder is producing a whopping 5 hp or so - about 40 hp to maintain the steady cruise. When the 4 cylinders are are shut down, the remaining 4 must now produce the same 40 hp, so they now each produce a whopping 10 hp/cylinder. Hardly a condition that is going to wear out an engine.

I don't know if they originally tested it for 100s of thousands of miles, but it been in production for 6 model years now, so its had a ton of field testing.

All that said, I still avoid it when on back roads by using the M shift mode because I don't like the repeated back and forth between V8 and V4 on hills and curves. Not because I think it hurts anything, but I can detect the changes in exhaust note and powertrain feel and do not care for it.

 

Nah....I am no Jay Leno, but I have about a dozen cars, including a 2021 C8 ......what I mostly drive is a 1999 Silverado 1/2-ton 4X4 regular cab regular box with about 210,000 miles.... runs like a Rolex....

 

hands down why this car is not a super car and is barely a sports car. No sports car should EVER drop cylinders while driving! I drive in "M" nice so it doesn't drop to 4 cyl but it's still a joke that chevy would do this and not also have the auto shutoff! 🤣 without the SOLER throttle controller this car would be extremely boring to drive.

 

Maybe they should add locking gas caps.

 

I've bitched about it a fair amount. I'm not worried about failures because of it in a C8. That really doesn't seem to be an issue with the LT2. And transitions are almost imperceptible. Everthying I've read about using different modes to get around it seem to have some sort of gotcha that you lose upper gears, or have to shift manually, or some other thing that makes me cringe. I'm running a Carbyte. I took my first long trip with it in the car about a month ago. I did notice the mpg was only around 26, where as that kind of driving with AFM got me around 30 mpg. I've often put performance catbacks on my fun cars, mostly for the sound. When I put a performance catback on my Silverado, it sounded like crap when it was in V4 mode. Got a tuner to eliminate the AFM. A lot of the aftermarket C8 exhausts include AFM valves to help with that issue, some don't and just use simulators. But if I was to spend money on an aftermarket exhaust I'd want to hear it full time. No AFM, no AFM valves

 

Sounds like this on each switch

 

I only know mine changes when the green V4 goes on or off. Silent.

 

The paranoia of Cylinder Deactivation is so crazy to me. People act like GM just through it in *****-nilly without knowing how it affects engines.

 

I had a LS2(L76) V8 engine in my personal Holden Commodore SS MY10 and put about 80k miles on it in 3 years. The AFM could not be disabled. It was running very reliable even with the very bad fuel quality in Australia. And very harsh environment conditions. Outback dust, high humidity forests, seawater in the air. Had about 18mpg over 3 years in average. Also all our V8 test cars & pool cars had AFM, no engine issues even treating them bad, like running high revs on cold oil etc.. Rather wear on the upholstery was an issue.

With the Eray I got about 19 mpg in Germany. (First 800 km) Which is not too bad considering running up to 135 miles per hour on the Autobahn.