Athena (P400485100021) 98mm 480cc Big Bore Cylinder Kit Yamaha WR 450 F 2007-2015; Yamaha YZ 450 F 2006-2009 Athena's Big Bore kit brings the raw power you have been missing in an easy to install, reliable package that bolts on with no machining needed in most cases, and includes easy-to-follow step-by-step installation instructions