CP Piston & Ring Set for Subaru EJ257 WRX STI- Bore (99.75mm)-Size (+0.25mm)- CR (10.0) - Set of 4

This is a set of four forged pistons and rings from CP Pistons, specifically sized for the 2004-2012 Subaru Impreza with the EJ257 engine. These pistons are a +0.25mm oversize, meaning they are 0.25 millimeters larger in diameter than the stock pistons, measuring 99.75mm. They are designed with a 10.0:1 compression ratio, which is a common target for performance builds that aim for improved power without sacrificing too much drivability on pump gas.

CP Pistons are well-known for their forged aluminum construction, which makes them significantly stronger and more durable than cast pistons. This strength is crucial for engines that see higher cylinder pressures, whether from forced induction like turbochargers or superchargers, or from increased compression. The set includes the necessary rings, which are essential for proper sealing between the piston and cylinder wall, ensuring good compression and oil control. Because these are an oversize piston, the engine block will need to be bored and honed to match the 99.75mm diameter before installation.

This set is a solid option for rebuilding or upgrading the EJ257 engine in your Subaru Impreza. Given the price point and the nature of forged components, these are typically chosen for performance applications where reliability under stress is a priority. Ensure your engine builder is aware of the oversize nature of these pistons and the required machining for proper installation.