The new cylinder reed intake 600cc (Rotax type 593) twin from Ski-Doo marks a
significant switch away from the rotary intake Rotax twins we have enjoyed for
so many years.
Why cylinder reed intake? Ski-Doo claims this design has all the
power of the case reed designs, with the advantage of being able to mount the
carbs up on the cylinders instead of down on the crankcase. This allows for zero
engine tilt, and an engine mounting position that is
lower and closer to the drive axle.
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Lowering and centralizing the mass was the
objective to reduce the moment of inertia and improve the handling. This design
change is critical to maintain vehicle cornering with today's long travel
suspensions and the higher chassis center of gravity they create.
This engine is completely all new. The cylinders have triple exhaust
ports, cast iron sleeves, and Rotax RAVE exhaust port
modifiers. The cylinder mounted reed cage has a very
large intake area and is really a hybrid between cylinder reed intake and case reed intake, with 70%
of the intake charge going directly to the crankcase and only 30% of the
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charge going under the
piston skirt (all of the high performance motocross bikes are using this design). The transfer ports
are large volume flow loop charged for excellent flow efficiency. A decompressor notch on the auxiliary
exhaust port allows for easier pulling over and starting of the engine. A high output 290-watt magneto
provides enough juice for the dual headlights, and there is enough room to house two trigger coils for
future development.
The new water pump design is claimed to force 50% more coolant into the cylinder,
keeping the coolant moving at a constant flow and
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