Multiair Part Time Two Stroke

The multiair system <link> is a mechanism used to vary valve timing and lift. It is essentially a hydraulic cylinder between the cam and valve. The cylinder is expanded by a spring but collapses unless the cylinder is filled with oil. This is similar to a hydraulic tappet or HLA, only there is solenoid switching available so that the oil flow may be precisely controlled. It looks like they can allow the cylinder to collapse to the extent where there is zero lift. <link>. If this is true, or could be made to be true, then you could drive the cam at twice the speed (which is crank speed) and use the multiair system to ignore one passage of the cam lobe and you are back to a functioning four stroke. Now, there's no real reason to drive the cam at that speed, unless perhaps you wanted to put lobes on the crank and throw the cam and associated parts out, which would be cool.

Now, they have fitted turbochargers to multiair engines. They also have coil-on-plug ignition and direct fuel injection all controlled from the ECU. Now that's all fairly standard stuff nowadays, but, if you had the ability to open the valves twice as often, you could convert to two stroke. If the engine is under high demand, and the turbo is providing pressure, you can simply convert the engine to a scavenged two stroke by actuating the valves twice as often, injecting twice as often and igniting twice as often.

Everything should scale, like the turbo will get twice the exhaust pulses to provide twice the intake air, the advantages being that you can develop twice the horsepower per revolution, which means half the RPM for a given power output. Cutting the revs in half should reduce a lot of the mechanical losses. You can also use the 2-4 stroke transition to do all sorts of clever things, ease gear changes by having a pulse of torque on upshift, the reverse on downshift. You could turn the engine into a fairly efficient air pump to keep the turbo spinning on the over- run.. all sorts of things.

This should enable the engine to start four stroke, increase RPM until the turbo produces positive pressure and instantly switch to two stroke. All the benefits of a 4 stroke turbo and a scavenged two stroke.