ymaha yzf450

For many years, the motocross world almost exclusively used two-stroke engines. AMA racing classes had two classes: 125 cc and 250 cc two-strokes, with no provision for four strokes. Most riders considered four-stroke engine technology to be antiquated and uncompetitive. Additionally, most four strokes produced very little power (the 1996 Honda XR400 made 32 bhp (24 kW), compared to the 40 bhp (30 kW) produced by most 250 two-strokes of the time).

In 1996, the AMA changed racing rules to allow 450 cc four strokes to compete in the same racing class as 250 cc two-strokes.Yamaha engineer Yoshiharu Nakayama first came up with the idea of creating the first competitive four-stroke race motocross bike.The Yamaha YZ400F was developed to fit into this category. It solved the power dilemma by borrowing superbike technology and giving the YZ a five-valve head, liquid cooling and a 12.5-1 compression ratio.

In 1997, Yamaha rocked the motocross world with the introduction of the YZ400M prototype, a concept motorcycle which borrowed much technology from road racing. The YZM was far ahead of all competition among four-stroke motocross bikes. Doug Henry piloted the YZ400M to its first victory in 1997 at the Las Vegas Supercross. This was the first time any four-stroke had won an AMA event.The YZ400M was the predecessor of the production YZ400F, which was released the next year.

September 8, 2009, Yamaha introduced its all new YZ450F with fuel injection . The engine is now rear-ward mounted, the crank rod angle has been changed to provide a more complete combustion, the 5-valve head is now a 4-valve head, the gas tank is located under the seat, the exhaust pipe is now a tornado exhaust pipe that lies under the seat, and the air intake is now in the front of the bike. They have a new bi-lateral frame which allows for new improved steering and the new engine components. The entire package comes together to create a bike that is mass-centralized like no other, and allows the bike to out-turn any other in its class. The bike was endorsed/introduced by James Stewart, and the bike is currently being tested by magazines.

Yamaha yz450f 2011, Yamaha updated the 2011

New for 2011: New clutch lever and pushrod for more consistent clutch feel during long motos http://www.yamaha-motor.com/sport/products/modelfeatures/209/0/features.aspx Dimensions

New for 2012: Revised fuel injection settings (mapping for injection and advance) offer smooth, controllable engine response in the low-to-mid-rpm range. New, longer 94 dB muffler. ECU programming is updated to optimize performance characteristics with the new-spec muffler. New front and rear suspension settings and valving deliver exceptionally smooth suspension performance. Dunlop® Geomax® MX51 tires provide great all-round traction. New seat foam material has an excellent cushion feel. Both color options feature rich-looking black rims and a gold-color drive chain.