Once running, though, the engine has a completely new personality. For the past couple of years, the YZ450F has been on the lazy side compared to the stout shooters from Kawasaki and Honda. But that was not all bad; the YZ's "easy" power was the favorite in our 2008 Vet MX comparison. Those vet riders will have to steady their wrists this year, though, because the new four-valve engine has sharper, harder-hitting low-end and midrange punch. Instead of a gradual flow of power from bottom to top, the YZ now has a more direct, "right now" delivery; and thanks to the injection system, the throttle response is instantaneous. This means power to the ground faster and better, making the bike quicker corner-to-corner, especially when that distance is short.