The two stroke engine produces more hp per pound than the four stroke engine. The two stroke engine consists of three moving parts, the piston, the rod and the crank. The piston acts as valve that opens and closes the intake and exhaust ports that are located on the walls of the cylinder.
Unlike the four stroke engine that fires only every other time of the pistons movement, the two stoke engine fires every time the piston reaches the top of its travel. This means that the time spent generating power is doubled in the two stroke engine than that of the four stroke engine, as there is no engine coasting during passive cycles. This is the main reason that the two stroke engine can rev more highly and produce more power (for its size) that the four stroke.