The length of the stroke, size of the bore, the speed in which air enters in, and the speed in which the air leaves, the air/fuel ratio, and the heat of the spark, and the number of cylinders, determines how much power an engine makes.
Hmm, I was gonna be a Smart-*** and ask some questions, like " what about rod ratio, ect, BUT you kinda Simply covered That in the "Speed in, Speed Out" deal... pretty cool, extremely simple explanation. Now the Fork?