CP Piston & Ring Set for Subaru EJ257 WRX STi - Bore (100.5mm) - Size (+1.0mm) - CR (8.2) Set of 4

If you're rebuilding the engine in your 2004-2012 Subaru Impreza WRX or STI, especially if you're pushing more power than stock, a strong set of forged pistons like these from CP Pistons is a smart move. These are designed for the EJ257 engine, which is known for its performance potential. Forged pistons are made from a solid block of aluminum that's heated and hammered into shape, making them significantly stronger and more resistant to detonation than cast pistons. This is crucial when you're increasing boost pressure or making other modifications that raise cylinder pressures.

This specific set is for a 100.5mm bore, which is a +1.0mm overbore from the factory size. This is often done to clean up cylinder walls or to increase displacement slightly. The compression ratio is listed at 8.2:1, which is lower than stock and ideal for boosted applications where you want to run more aggressive timing and boost without risking detonation. CP Pistons are well-known in the performance world for their robust construction and precise manufacturing. They come with rings, which simplifies the rebuild process, as you won't need to source those separately. Remember that installing pistons is a critical engine building task; ensure your machine shop has prepared the cylinders correctly for this overbore size and that you follow proper engine assembly procedures.

This set includes four pistons and the necessary rings to match. It's important to note that these are not CARB approved and cannot be shipped to California. If you're building a high-performance EJ257, investing in a solid set of forged pistons like these is a foundational step for reliability and power.