Like its motocross-focused YZ450F counterpart did in 2020, the Yamaha YZ450FX received several updates for the 2021 model year. Engine-wise, this included an all-new cylinder head that is 10mm lower with a claimed 0.67-pound decrease in weight. Internally, the camshafts were lowered 6mm and positioned 14mm closer together, the valve angle is 7 degrees more upright, the valve stems are 6mm shorter, the exhaust camshaft working angle was decreased by 2 degrees, the intake and exhaust port shapes are new, and the airflow rate at mid-to-high valve lift was increased.
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A reduced combustion chamber volume, increased compression ratio (from 12.8:1 to 13.0:1), new piston design with a recessed crown shape, 1.5mm-longer connecting rod, and exhaust header pipe diameter increase of 3.2mm at the connection joint are the majority of the changes made to the powerplant of the bLU cRU’s flagship cross-country racer for 2021. What was Yamaha’s goal in making them? More controlled acceleration feeling at small throttle openings, and stronger and longer- pulling power. How did the 2021 YZ450FX perform on Dirt Rider’s in-house dyno? We documented peak figures of 53.0 hp at 9,600 rpm and 32.9 pound-feet of torque at 7,100 rpm.