CP Piston & Ring Set for Subaru EJ25 WRX STi - Bore (99.75mm) - Size (+0.25mm) - CR (10) - Set of 4

If you're rebuilding the engine in your 2004-2012 Subaru Impreza, especially for performance applications, a solid set of pistons is crucial. This set from CP Pistons is built for the EJ25 engine, commonly found in WRX and STi models, and is designed to handle increased stress from tuning and demanding use. These are a +0.25mm oversize set, meaning they're intended for an engine block that has been bored out to 99.75mm to refresh cylinder walls or increase displacement slightly.

CP Pistons are well-known in the performance world for their strong construction. These pistons are forged from high-strength aluminum, which is lighter than cast aluminum and much more resistant to deformation under high heat and pressure. This set features a 10:1 compression ratio, a popular choice for modified EJ25 engines that balances power output with pump gas compatibility. The included rings are specifically matched to these pistons to ensure a proper seal in the cylinders, which is vital for engine health and performance. Because these are an oversize piston, they require machining of the engine block to ensure a precise fit and optimal performance.

This set includes four pistons and their corresponding ring sets, ready for installation into your EJ25 engine. Remember that installing oversize pistons requires professional machining of your engine block to the exact bore size specified. It's also a good time to inspect and potentially replace other engine components like bearings, gaskets, and seals to ensure a complete and reliable rebuild.