2005 Ski-Doo Racing Handbook, Page 46Get this manual
SECTION 03CHASSIS PREPARATION
Valving and Dampening In the HPG shock, the piston passages are covered by stack of thin metal shims of various thicknesses and diametersThe shims provide dampening by acting as spring loaded valves offering resistance to the oil traveling through the pistonThere is stack of shims on both sides of the pistonOne side controls compression dampening and the other side controls rebound dampeningBy varying the number and thickness of shims the dampening characteristics can be very accurately obtainedThere may also be orifices or slits in the piston that are not covered by the shimsThese are referred to as bleed slitsThe size and number of these slits will also affect dampeningThe external adjustment on the MVA, HPG shocks is variable bleed holeRebound dampening will usually be much stiffer than compression dampeningThis is because rebound dampening must resist the force of the spring and because piston speeds are much slower during reboundAt low piston speeds, the number of bleed slits will have fairly large effect on dampening, but as piston speeds increase most of the dampening is controlled by the shim stackThis is because the flow area of the slits is much smaller than the flow area under the shimsSince only small amount of oil can flow through the bleed slits (compared to the amount that flows under the shim stack), the slits have only very small effect on dampening at high piston speedsBecause of this characteristic, bleed slits are most effective on rebound dampeningThey will have only very slight effect on compression damping because the typical piston speeds on compression strokes are several times faster than on rebound strokesThere really is no such thing as high speed rebound dampening