Liquid-cooled DOHC 4-stroke; 4 titanium valves
The Yamaha YZ450F is a four-stroke racing motocross bike built by Yamaha Motor Corporation. It was the successor to the previous YZ426F which was discontinued in 2003. It is credited by Cycle World and Dirt Rider magazines as the bike that started the four-stroke dirt bike revolution.[1][2] The 2006 YZ250F and YZ450F were the first production motorcycles equipped with titanium suspension springs.[3]
The YZ450F received a major update in 2006, with over 300 parts changed and improved. The power was smoothed out, and the bike was made easier to ride, putting to rest the complaint that the YZ had too much power.[13] The transmission was returned to a more traditional five-speed. An all-new aluminum single backbone frame shaved another 10 pounds off the weight.