2005 Ski-Doo Racing Handbook, Page 128Get this manual
SECTION 05ENGINE PREPARATION
ENGINE TUNING CAUTIONS
Here are few items to keep in mind when working with your engineIf you are in stock classes, know what adjustments are legalModifications to the power curve of an engine will require recalibration of the transmissionThe lower the RPM at which you can generate the torque you need, the higher the percentage of that power that will reach the trackSloppy engine modification usually results in less power than you had stockUse the proper octane gasoline for your engine (Modification may require higher octaneCorrect your carburetor jetting for the atmospheric conditions which exist at the time as close as possible to the time you will be competingFollow the assembly and disassembly procedures outlined in the appropriate Shop Manual
BASIC ENGINE THEORY
Terminology
CYCLE In combustion engine, cycle is accomplished when the four (4) phases; intake, compression, ignition and exhaust are completeTop Dead Center: The position of the piston when it reaches the upper limit of its travel inside the cylinderBTDC: Before Top Dead Center ATDC: After Top Dead Center Bottom Dead Center: The position of the piston when it reaches the lower limit of its travel inside the cylinderBBDC: Before Bottom Dead Center ABDC: After Bottom Dead Center Diameter of the cylinderThe maximum movement of the piston from BDC to TDCIt is characterized by 180 of crankshaft rotationSpace between cylinder head and piston dome at TDCThe volume of the cylinder displaced by the piston as it travels from TDC to BDCThe formula is: Bore Stroke 20 -4