The redesigned PowerBomb is a four-stroke header that incorporates FMFs patented PowerBomb module at a precise location in the initial stage of the header. By positioning this Bomb at a key point in the system, increased performance and flow is achieved through the expansion and contraction of exhaust sonics through the system. Result is a flow increase of nearly 10%! Theouter chamberin the Powerbomballows the air to expand, cool and ramp back up at a higher velocity. Additionally, the PowerBomb is a pre-muffler of sorts which helps to lower the bikes sound output by providing more sound absorbing surface area for the sound medium (exhaust gases). On some models, you can choose between a moto or supercross version. The supercross version is designed for more low to mid-range power where the moto version is focused in the mid to upper RPM range. APPLICATIONS Make Model Year YAMAHA WR250R 08-20 YAMAHA WR250X 08-11 Fits: Yamaha WR250R 2008-2020 WR250X 2008-2011