This YFZ450 air filter kit fixes the standard air filter's problems and adds significant horsepower at the same time. The kit includes an oversize precision fit adaptor plate which is 25% larger in the throat than the standard plastic plate, oversize K+N style filter and filter cover. Eliminates the restrictive stock mesh cone and provides a positive clamping filter. All these items replace the dodgy standard filter system and let you still run the airbox.