I think if you leave any of the valves open, you get a significant drag from the air going in and out. Keeping everything closed lets the the piston just bounce against an air spring.

 

...and, this also sounds correct, from someone like me who simply is going off what I'm seeing in the video.

Man, all the damage possibilities are going to have me seeking the one avenue that is surely working, namely get a VCM defeat device and install it.

The original VCM (the engine in the video is an 05) does not stay activated "for a short time". If you drive 300 miles at speed with no stops or slowdowns on the highway, 3 cylinders would be de-activated the ENTIRE time.

Holy moly. That is worse than I could imagine.

OF

 

I've always wondered about cylinder deactivation methods like VCM, why all ports are closed? Why do they not keep at least one exhaust port open to relieve the vacuum/compression on the deactivated cylinders?

 

Man, I agree with that. Or, at least do like you say in a "modified way", with the VCM exhaust cam profile having a very slight opening at a good time, instead of a totally "flat" profile, as mentioned by the maker of that video.

OF

 

I had no idea the valves all stayed shut on the respective deactivated cylinders. With VCM activation, there is a relatively lesser amount of pressure on the piston upstroke (compared to an operating cylinder's power stroke) and a much more considerable amount of vacuum on the piston downstroke of the deactivated cylinder (compared to a normal intake stroke) as it continues to reciprocate in its cylinder with closed valves.

The oil control rings are your "windshield wipers" for the cylinder walls. They're designed to work where they only have to deal with just one not-considerable vacuum stroke (through open valves ) out of four strokes, namely the intake stroke. With cylinders deactivated by closing all valves, that cylinder is pulling a much more significant vacuum every time it is pulled down .... because of the closed valves not allowing any air into the cylinder. No wonder so much oil-entrained air from the crankcase gets pulled past the piston oil control ring, where it can get into the compression ring lands in quantities that those rings were never meant to handle. Sludge formation is an eventual and inevitable problem? Does that then causes the rings to quit their normal rotation within the ring lands that sit above the compression ring, thus losing their ability to keep those piston ring lands clean? If that happens, I can't imagine that cylinder sustaining normal compression values.

I always knew that incorrectly functioning oil control rings can lead to sludge contaminated compression rings, but I had no idea that cylinder deactivation left the valves completely closed.

So, does the following mechanism for the ensuing VCM problem make sense?

1.) VCM activation causes the reciprocating motion of the piston in the deactivated cylinder to pull oil-entrained air out of the crankcase due to hella more vacuum.
2.) Oil-entrained air gets past the oil-control ring where it deposits oil into the ring lands of the compression rings, and gets into the combustion chamber.
3.) Eventually, the normal circular motion of the compression rings is halted by an excess of contaminants accumulated in their ring land (and they then don't function well.)
4.) Also, with oil on the wrong side of the rings, the spark plugs are more likely to become fouled.

Fatlard, thanks for the video. I just bought a used 2012 Honda Accord EX-L V6 with about 78,000 miles on it. It's running well (for now). It has VCM. It's time for me to buy a VCM defeat device.

OF

 

With cylinders deactivated by closing all valves, that cylinder is pulling a much more significant vacuum every time it is pulled down .... because of the closed valves not allowing any air into the cylinder.

It’s insane... from speedkar9 video.. any car with VCM need it’s disable like yesterday...

 

Waiting for someone to come along and just see the rear rebuilt head looking all clean and going "Hey, obviously VCM actually cleans your cylinders, look at how clean it is. I'm not going to muzzle"

I'm a bit disappointed that he acknowledged the existence of muzzlers briefly but didn't suggest it at the end.

 

Guy knows his stuff. Mechanical engineer.