450cc meaning 450 cubic centimeters, is an engine size of some motorcycles. It is most popular for four-stroke dirt bikes, because an AMA rule in both Supercross and Motocross, is that bikes that use a four-stroke engine are allowed to have 450cc engines. Two-stroke engine using bikes are only allowed a 250cc engine in the same class. As a result, 250cc two-stroke engines are rarely ever used professionally.
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