[SOUND] I'm Brian Cooley with CNet on cars, taking some of your emails about high tech cars and modern driving.
Let's see, this first one comes in from Will, who says we're seeing more and more cars with cylinder deactivation technology to deliver more efficient driving, but how does it work?
Do the cylinders actually stop moving?
Is it some sort of physical connection from one bank or the other?
Or some kind of electronic shutdown.
Well Will, cylinder deactivation has been around for quite a while.
It's been done different ways.
Let me tell you what the current state of the art it.
It's sort of a misnomer.
Cylinder deactivation deactivates the entire cylinder piston assembly.
But it is not piston deactivation.
The piston inside of the cylinder Keeps going up and down.
There's a mechanical connection there that is simply too hard to break.
It would require some Jules Vernian apparatus to cause that to disconnect and literally stop moving.
Instead what we do is we turn off the fuel going into the cylinder, and we turn off the spark.
Inside the cylinder, which can cause drag in two ways.
First of all, you've got the piston rings, those are causing friction on the cylinder wall.
Can't get around that.
But what you can do is you can park the valves open, because modern cars have the These elaborate, addressable valve trains that can tell the valves stay open in a breathing mode so at least that dead cylinder isn't putting all the work into compressing air all the time, which would cause a lot more drag on the engine.
Overall this system while not perfect can make some really good MPG gains.