[Arny Krueger]

"Don Pearce" wrote in message
...
On Thu, 25 Oct 2007 05:56:37 -0400, "Arny Krueger"
wrote:

A cylinder in a gas engine uses more energy if it is only partially in use
than if it is turned off. Some losses stay about the same, but other
losses
are vastly reduced if you partially turn the cylinder off by means of
significantly altering the valve timing. AFAIK, the spark plug still fires
but no fuel is injected, and the amount of air that the cylinder pumps is
vastly reduced.

In the huge diesels that routinely turn off multiple cylinders, the
valve gear is uncoupled so the valves remain closed.

Thats about the same as what they do in the cars I mentioned.

That way no air
is pumped and the losses drop to negligible levels.

Agreed.

You really don't
want to be shifting air, even if there is no combustion, if economy is
your objective.

That seems to be how the technology works. I am informed by my friends who
have cars that implement this strategy, that there are consistent and
significant real-world fuel economy gains, as measured by modern car
computers that display dynamic fuel economy measures.