CP Piston & Ring for Subaru EJ257 WRX STi-Bore (100.0mm)-Size (+0.5mm)-CR (9.0) *SINGLE PISTON/RING*

If you're rebuilding the engine in your Subaru WRX STI with the EJ257 engine, a single forged piston like this one from CP Pistons is a solid choice for getting back on the road. This piston is designed for a 100.0mm bore and comes at a +0.5mm size, meaning it's slightly larger than stock to account for bore wear or to achieve a specific build target. It features a 9.0:1 compression ratio, which is a common target for modified EJ257 engines looking for a balance between power and reliability.

CP Pistons are well-known in the performance engine building world. This particular piston is forged, which means it's made from a solid block of aluminum that's heated and hammered into shape. This process creates a much stronger and more durable piston than cast aluminum, making it ideal for engines that see hard use or are built for increased horsepower. The +0.5mm sizing is important to note; it's intended to be used when the cylinder bore has been machined to match this dimension, often during an engine rebuild to ensure a proper seal and optimal performance. This piston is sold individually, so be sure to order the correct number for your engine.