More info................
The really neat thing is the fact that they are 2 stroke engines , the liners have intake ports on the bottom edge . however unlike your standard dirt bike engine they have an exhaust valve. the intake air comes from multiple turbochargers , usually the size of a small buick . i would guess the engine in the original link would run 3 or 4 of them . At the bottom of the power stroke the piston uncovers the ports and the turbo drives air up through the liner and scavenges the spent gas through the valve and into the exhuast pipe (no lost fuel charge ,just how the EPA likes it, you will see this technology on dirt bikes and snowmachines before too long). the valve is then timed to close before the piston starts up so as to pressurize the cylinder before compression starts . valves are opened by a cam driven oil pump acting against an air spring . no springs to wear out , no lash to set . valves can be removed for service independent of the head.
To go astern the engine is stopped and the cam shifted and then the engine is started again running the opposite direction just like some of the newer snowmachines introduced in the last few years. starting is by direct air injection . compressed air at 20 kg/cm (300psi)is directed into cylinders on the power stroke , once the engine reaches a set rpm the fuel is cut in and off she goes . peak engine speed on my ship is around 100 rpm , you can hear individual cylinders fire and exhaust valves open and close definately different than anything you find under the hood of any buick.