Yamaha YZ250 YZ250X WR250 Phathead cylinder head kit 1999-2026

Yamaha YZ250 Phathead cylinder head kit 1999-2026 Chamber selection: Y20 - 22cc Stock compression for the X model Y21 - 21.1cc Stock  (91+ octane) Y22 - 20.1cc (100+ octane) Y23 - 19.1cc (105+ octane) YZ295 - 72mm 91+ octane 23.8cc YZ296 - 72mm 100+octane 23cc 72mm chamber Does not fit Athena       Phathead Kits include a head shell with one combustion chamber, two sets of o-rings, cylinder head nuts, copper washers, some stickers for your bike and tool box and installation instructions.. Phathead cylinder heads are made of 6061 T6 billet aluminum.  The material is stronger and transfers heat better than cast aluminum.  The two piece design allows an increase in coolant flow as well as surface area which improves cooling for better consistency and performance.    The O-ring design eliminates the need to use a gasket.  You can swap chambers without the cost of replacing gaskets.  One of the main benefits of the product is the replaceable combustion chamber which are available in a range of compression options. Suggestions : Swap chambers to adjust performance for a variety of riding conditions and track types or keep a spare in case of engine failure.