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
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.