sonnie

Does anyone know if the same cylinders are shut down when the engine reverts to V4, or is it random ...

Jim Barker

Same ones on a 10 min duty cycle on and 1 min off cycle if your steady Driving such as Interstate. Third gear and up on auto/ 4th gear and up manual and only in economy mode. All modes in Auto just a little less aggressive as you work toward track mode.

sonnie

So its ALWAYS the same cylinders that shut down, just on a cycle sequence.

Jim Barker

Yes, solenoids bleed oil from those lifters which stops the valve action on those same cylinders. Not sure if its both valves in those cyl.

sonnie

Seems that would cause some unusual wear patterns on those cylinders not to mention the lack of combustion deposits long term on the cylinders firing vs. the ones that don't..

On a recent 400 mile round trip, I have found very little difference between mpg with system on vs. off.. Seems like an engineering practice in futility not to even mention the addition of all those extra systems that could eventually fail.

Rkreigh

you still have frictional and some efficiency losses to realize the small but measureable gain

as these engines are already very efficient, the trade off is still worth it

I don't know as the newer systems are all that unreliable, so I would either deactivate it if you are concerned or leave it be

it's done some pretty admirable durability testing

DavePowell

From the GM videos, the middle two cylinders on the passenger side and the outer two on the driver's side are shut down. Both valves are closed by routing oil pressure to the eight special lifters and close those valves, so each cylinder becomes a spring. Just stopping injection would leave substantial pumping losses since a four-stroke engine is essentially a pump and would waste energy pumping air through it.

I read that BMW won't go to cylinder deactivation because it would cause uneven wear patterns. Time will tell.

Jim Barker

At best on all my driving a 2 mile per gallon increase is all I see. Speed makes a bigger difference since mine falls off to the lower 20's at those speeds now seen on interstates from a high of 33 mpg at 65 mph. Thats two people with luggage on a vert. Maybe the eight speed does better in the 80 mph range and also the manual.

sonnie

Don't know why GM engineers even added this feature to a true sports car. All the Corvettes with LS engines have never really had a problem concerning fuel economy, and all the ones I have owned starting with LS-1, LS-2, and LS-3 got a minimum of 30mpg when touring. This new engine has a real problem with 30mpg even with the cyl-deactivation on. When the system is de-activating, u also lose that distinctive Corvette sound in Sport mode.

Jim Barker

When I picked up my car 500 miles from home I drove it in Econo mode most of the time and the DOD drove me crazy. After several thousand miles and complaining, local dealer told me to quit driving it in that mode. Touring does help a little with less aggressive perimeters. I believe it would be less intrusive if 3rd gear was changed to not allow same as manual shift cars. This would help with lower speed operation where I have the driveability issues

sonnie

There is also a problem with the new 8-spd auto and the DOD.
When you are cruising at speed in auto mode and put the throttle down hard, the DOD doesn't transition to V8 before the transmission drops down and you get a bang in the driveline.. The first time it happened to me, I thought I broke something...