CP Piston & Ring Set for Subaru EJ257 WRX STI - Bore (100.5mm) - Size (+1.0mm) - CR (8.5) - Set

This is a set of four forged pistons and matching rings for your 2004-2012 Subaru Impreza WRX or STI with the EJ257 engine. These pistons are designed to be 1.0mm oversize, bringing the bore to 100.5mm, and feature a compression ratio of 8.5:1. This setup is commonly used when rebuilding or upgrading the engine, especially for those looking to handle increased boost or higher performance demands.

CP Pistons is known for making well-built engine components, and these forged pistons are no exception. Forged from high-strength aluminum alloy, they are significantly stronger and more durable than cast pistons, making them ideal for high-performance applications where heat and stress are greater. The 8.5:1 compression ratio is a notable change from stock, which can be beneficial for forced induction setups, allowing for more boost pressure before detonation becomes a concern. The included rings are specifically matched to these pistons to ensure a proper seal within the cylinder bore.

When installing these pistons, it's important to ensure your engine block is properly machined to the 100.5mm bore size. Proper ring gap setting and piston-to-wall clearance are critical for engine longevity and performance. This set is designed as a direct fit for the specified Subaru models, simplifying the installation process for a qualified mechanic. Please note that this part is not CARB approved and cannot be shipped to California.