snowmobile clutch systems are designed to rev up to a Rpm set by the manufacturer and stay there while the clutches shift up and increase your speed. this is under full throttle conditions. I could right a book on it but Olav Aaen allready did and it is very informative. It is called Olav Aaen's clutch tuning Handbook.
This along with his carb tuning handbook are in my oppinion must have books they are around $20.00 a piece and well worth every penny.