The amount of power increase with an increase in displacement is a curve, it gradually peaks out. A single cylinder can only make so much horsepower. Thats why a twin cylinder engine makes roughly 20% more power than a single cylinder engine of the same displacement. You can only go so big before reciporcating mass gets to big, and the volumetric effeciency goes downhill. Thats why a Rotax 600cc two stroke triple can make 160hp, while a single cylinder 600cc two stroke would be hard to get over 70hp. BTW, those 600cc Rotax triples are one badass motor... friends got one in a Skidoo Mach III. WOW... pin the throttle, tach edges up to about 9500rpm, skis are in the air till about 70, and your doing 130 before you know whats going on. What a ride!!!