CP Piston & Ring Set for Subaru EJ257 WRX STi - Bore (99.5mm) - Size (STD) - CR (9.0)

If you're rebuilding the engine in your 2004-2012 Subaru Impreza WRX STI, especially if you're looking to handle more power or replace worn components, a solid set of pistons is crucial. This forged piston and ring set from CP Pistons is built for the EJ257 engine, offering a standard bore size of 99.5mm and a compression ratio of 9.0:1. This setup is designed to be a direct replacement for your stock pistons, making the rebuild process smoother.

CP Pistons are well-known in the performance engine building world. These aren't cast pistons; they're forged from high-strength aluminum alloys, which makes them significantly more durable and resistant to the stresses of higher horsepower applications compared to stock. The 9.0:1 compression ratio is a good balance, providing a noticeable bump in performance while still being manageable with most pump gas tunes. This set includes the pistons and the necessary rings, so you have the core components ready for your engine build.

When installing these pistons, ensure your cylinder bores are perfectly clean and honed to the correct specification for the rings. It's also a good idea to have your connecting rods checked and balanced before assembly. This set is a strong foundation for an engine that needs to perform reliably under demanding conditions.