Here is the big bore kit proposed by ATHENA to increase the displacement of your motocross / enduro YAMAHA WRF 450cc 4 stroke from 2003 to 2006 / YAMAHA YZF 450cc 4 stroke from 2003 to 2005. This kit in Ø98mm against Ø95mm of origin thus makes it possible to pass your motor bike of 450cc has 478cc real! A gain of torque and performance will be immediately felt. It allows a gain of 2 HP on average which is huge on this vehicle. Enough to have fun on the tracks or in the forest. ATHENA has moreover well planned things because this top engine is sold complete. It includes the cylinder, piston, ring as well as all the gaskets you need for a quality and tight reassembly. The advantage of taking this engine is that it is designed to be mounted on the original connecting rod with the original cylinder head and camshaft. So you don't have any modification to do ! Here attached the power curve so that you can see by yourself the difference between the original and the big bore. You will also find a detailed list of vehicles on which this cylinder can be mounted.