Pioneered by the reviled GM on the 1981 Cadillac 5.7 V8. Reintroduced by GM in 2001 and used ever since. Chrysler put it on their V8 around 2003.

Mitsubishi played around with it on 4 pots around 2000-and took it off because the fuel savings weren't worth the increased NVH problem.

Doesn't stop the PR mem from claiming to have reinvented the wheel.

The idea is that under light loads (not overrun) you shut off two cylinders so that there is no pumping losses across those cylinders. This increases manifold pressre for the other two cylinders which increases overall efficiency. It does work although the gains are modest. Instantaneous fuel injection rate is of course irrelevant to fuel economy.

Oh yes, you still get all the friction from the inactive pistons-just the pumping loss that goes.

It works really well with pushrod designs because you simply use a collapsible hydraulic lifter-the rest of the valvetrain is entirely conventional. Not quite as easy with direct acting designs.

Yes I was aware of the GM work in this area. I was just questioning the suggestion that it helps on the overrun as the fuel would be cut anyway when the throttle is closed. Keeping the exhaust valve(s) open when the cylinder is being cut would of course offer the best efficiency gains due to reducing pumping loses, but you'd have to be very careful not to disturb the gas flow for the active cylinders destroying scavenging. Just cutting the spark will reduce plant food production I can't see it saving fuel with a cruising car due to the pumping loses from the deactivated cylinder. Looks like more technology and needless complexity to keep the green fraud going without actually benefiting the driver or the environment.