CP Piston & Ring Set for Subaru EJ257 WRX STi - Bore (99.75mm) - Size (0.25mm) - CR (8.2)

CP Pistons is well-known for making strong internal engine components, and this forged piston and ring set is a prime example of their work for the Subaru EJ257 engine. If you're rebuilding the top end of your 2004-2012 Subaru Impreza WRX STI, these pistons are built to handle the demands of a performance engine. They come in a 99.75mm bore size, which is a 0.25mm oversize, and feature a compression ratio of 8.2:1, making them suitable for boosted applications where you need to control detonation.

Forged from high-strength aluminum, these pistons are significantly more durable than cast pistons, offering better resistance to heat and pressure. This makes them a solid choice for builds that push beyond stock power levels. The set includes the pistons and the necessary rings, ensuring you have the core components ready for installation. The 8.2:1 compression ratio is a notable change from stock, designed to work well with forced induction systems, allowing for more boost without excessive cylinder pressures that could lead to pre-ignition.

When installing these pistons, it's important to follow the manufacturer's recommended clearances and torque specifications. Because these are an oversize piston, proper cylinder wall preparation is crucial for a good seal and long engine life. This set is designed as a direct fit for the specified Subaru Impreza models, simplifying the installation process for a performance rebuild.