v8 to v4 ? whats actually does it change ?

obviously the fuel is restricted, BUT
 
do the valves float free ?  allowing for no compression ?
 
I cannot find out ANYWHERE

Saw a marketing release a couple years ago when it was still called DOD (displacement on demand).  Not sure what has changed, but at that time they said it was simply cutting off air / fuel to 4 of the cylinders.

Cuts fire and fuel to 4 cylinders. The way I understood it when I first saw it is that it has an electronic valve that opens and disallows compression.

"We disable the valves through a device called a switching lifter," explains Meagher. "This differs from a normal lifter in that there is an inner body and an outer body connected by a spring-loaded pin. For V-8 operation, the pin is fully expanded by the spring so the two pieces act as one and the lifter acts like a regular lifter. When we want to disable the valve operation, we deliver high-pressure oil to a groove in the lifter that leads to the outside end of the pin, forcing the pin to collapse the spring. Now the two parts of the lifter are free to move relative to one another and as the cam lobe pushes on the follower the inner portion of the lifter pushes against another spring at the top of the lifter and does not transfer force to the pushrod."
 
 
http://www.superchevy.com/technical/engines_drivetrain/accessories_electronics/0405sc_gmdod/index.html