A powerhouse since 2010 when the Yamaha engineers reversed the engine and created a straighter, downdraft intake, the new YZ450F gets a slightly straighter (more vertical) intake tract and higher-lift cams. The intake valves now open earlier, open farther, and stay open longer, with the aim of increasing midrange and giving a torquier character. Overlap, when both valves are open, has been increased in an effort to improve top-end and over-rev. The throttle body is now a Mikuni unit (a switch from Keihin), with a push-on cold-start knob that releases with a twist of the throttle. The piston is now a bridge box style, lighter by 2.3 percent and with a compression bump (12.8:1 versus 12.5:1), and the new exhaust header is 12mm longer and narrower at the junction (38mm diameter versus 41mm). There’s even a new spark plug with a longer electrode for improved burn efficiency and a cap holder on the valve cover. According to Yamaha, the changes mean an overall horsepower boost and claimed 3 more ponies at both 6,000 and 9,000 rpm.