2005 Ski-Doo Racing Handbook, Page 129Get this manual
SECTION 05ENGINE PREPARATION
Combustion Process
NORMAL COMBUSTION Since the beginning of this study we have spoken of airfuel mixture combustion rather than explosionThis combustion is slow then accelerated burning of the mixture within the combustion chamberIgnition occurs with the firing of the spark plugThis initial process generates heat and pressure which in turn, is transmitted by conduction to the contiguous portion of the unburned mixtureWhen this portion has reached the point of selfignition it starts to burn releasing more pressure and heatThis burning action, called flame front, travels at speed of approximately 30.3 (100 feet) per second until all mixture is burned, thus providing maximum piston thrust