CP Piston & Ring Set for Subaru EJ257 WRX STi - Bore (100.5mm) - Size (+0.5mm) - CR (9.0) Set of 4

If you're rebuilding the engine in your 2004-2012 Subaru Impreza WRX STi, this set of four forged pistons and rings from CP Pistons is a solid choice for performance applications. These are designed for the EJ257 engine, featuring a 100.5mm bore, which is a +0.5mm oversize from the factory specification. The compression ratio is set at 9.0:1, making them suitable for boosted applications where a slightly lower compression can help manage detonation and allow for more aggressive tuning.

CP Pistons are well-known in the performance world for their robust construction. These pistons are forged from high-strength aluminum alloy, which offers a better strength-to-weight ratio compared to cast pistons. This means they can withstand the higher cylinder pressures and temperatures common in modified or performance-tuned engines. The included rings are matched to the pistons and bore size, ensuring a proper seal for optimal compression and oil control. Remember that installing oversize pistons requires honing the cylinders to the correct size, so be sure your machine shop is aware of the +0.5mm requirement.

This set includes all four pistons and their corresponding ring sets, ready for installation. Please note that this part is not CARB approved and cannot be shipped to California. Always refer to your engine builder's specifications and the manufacturer's installation instructions for proper assembly and break-in procedures.