From what I've seen on the Fiats using that technology, it causes odd idle behavior because of a lack of oil pressure. This seems like an implementation issue, and not a failing of the general design itself so it should be possible to avoid.
In general, it's a pretty good improvement on typical variable valve systems. And they could get the exhaust cam going too pretty easily.
You lose one cam, which is a nice thing to lose (complexity, friction, etc.), and you gain infinitely adjustable valve lift which makes the fact that duration is not really adjustable a non-issue.
That being said, I'd take a solenoid control system like in the Koenigsegg video over the Fiat or any other hydro/mechanical system any day of the week.
However, ultimately all of these systems still control
poppet valves so it really doesn't excite me as much as seeing those things done away with. If you could design a
rotatry valve system that seals properly (I assume that is the limiting factor right now) then you would see HUGE gains in efficiency across the board.
1) The air would move from the intake runner into the combustion chamber uninterrupted by a huge poppet valve in the way which should provide cylinder filling like we've never imagined before.
2) Rev limits would be determined by the limitations of the bottom end now instead of the valvetrain limitations. 10,000-20,000 RPM redlines would be no problem.
2.1) They could be mated to each other and controlled mechanically similar to a camshaft (but almost frictionless and no additional moving parts). The mechanical setup would run at 1/4 engine speed, which is half the speed of a camshaft, which allows for even less lubrication needs, etc.
2.2) Or they could be controlled electrically with a stepper motor and each valve could be controlled independently of the valves of the other cylinders.
2.2.1) Electrically controlled versions would provide simple and easy cylinder deactivation.
2.2.2) Electrically controlled versions would also remove the need for the throttle body.
3) Packaging could probably be improved too by cutting the height of the head in half. The head would only need to be as tall as the rotary valve shaft itself. Maybe 1 or 2" max.
4) They would never interfere with the pistons, so valve timing issues would not cause physical damage to the valves nor pistons. No more interference engines!
There is one rotary valve system that seems to work (
link) but it is so convoluted that it doesn't provide most of the gains you would expect to see in a proper rotary valve setup. (The air path does not get a straight shot from the intake manifold runner into the combustion chamber, it has to travel through four (!), tight, 90-degree bends between the intake runner and the combustion chamber.)
Koenigsegg's Camless Motor
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Originally Posted by BenFenner 
. I didn't know it was to the point of being actually used in a car.
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