The 426 also includes a larger pivot shift for increased durability. A larger rear brake disc was also added which means greater stopping power. Third generation YZ450F 2003–2005 For 2003, the YZF received the biggest update in its history. First, the engine displacement was increased with 449 cc in compliance to the new AMA Motocross maximum displacement rule, the engine now produced over . Next, the frame and plastic were updated for a new, sleeker look. Additionally, the YZF's weight was decreased from its original to . The bike made tremendous power; however, many thought that the bike had too much power for a motocross track. The 2005 YZ450F was the first YZ450F to feature KYB twin chamber cartridge forks. Fourth generation YZ450F 2006–2009 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. The transmission was returned to a more traditional five-speed. An all-new aluminum single backbone frame shaved another 10 pounds off the weight. The 2006 saw KYB SSS forks. 2007 saw camshaft and exhaust changes, moving power from low-RPMs to mid-RPMs. 2008-2009 furthered pushed the powerband towards the mid-RPMs. Fifth generation YZ450F 2010–2013 September 8, 2009, Yamaha introduced its all-new YZ450F with fuel injection. The engine cylinder is rearward slanted, 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 exits the rear of the cylinder, 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. The bike was introduced by Yamaha Factory Motocross rider James Stewart Jr. The top speed has been recorded at 80 mph stock. Sixth generation YZ450F 2014–2017 The 2014 YZ450F was a new design the retained the backwards slant engine. The 2014 model has a wet-sump engine and an easy access air filter. Seventh generation YZ450F 2018–Present The 2018 YZ450F features electric start and a Mikuni fuel injection system. The kickstarter was removed for this generation. References External links The Long History of Reverse-Cylinder Engine Designs - motocrossactionmag.com YZ450F