CP Pistons SC7420-4 Forged Piston & Ring Set for 2004-21 Subaru EJ257 WRX/STI

Vehicle Fitment

• 2004-2021 Subaru WRX STI (EJ257)
• 2006-2014 Subaru WRX (EJ257)*
• 2009-2013 Subaru Forester XT (EJ257)*

Features

• High-strength forged aluminum pistons built for boosted performance
• Designed for larger bore applications (standard 99.5 mm or oversize options)
• Deep valve reliefs for high lift cam compatibility
• Accumulator grooves to improve ring seal under boost
• Double pin oilers for enhanced lubrication around wrist pins
• Fully CNC machined and balanced for precision and durability
• Includes piston rings and wrist pins
• Ideal choice for rebuilds, high-boost builds, and performance engines

Specifications

• Part Number: SC7420-4
• Bore Size: 99.5 mm (standard) - oversize variants also available
• Compression Ratio: ~8.2:1 (standard set)
• Stroke: 79 mm
• Rod Length: 130.5 mm
• Piston Material: Forged 2618 aluminum
• Ring Pack: Typically 1.2 mm/1.2 mm/2.0 mm
• Quantity: Full set of 4 pistons with rings
• Intended for high-boost turbo and performance applications

Included Components

• 4x Forged pistons (99.5 mm size)
• 4x Piston ring sets
• 4x Wrist pins

Product Description

The **CP Pistons SC7420-4** forged piston and ring set is engineered for Subaru performance applications using the **EJ257** 2.5 L turbocharged engine. This premium performance kit features high-strength forged aluminum pistons designed to handle the demands of elevated combustion pressures typical in high-boost, tuned, or race engines while maintaining durability and reliability. The set comes at a standard **99.5 mm bore with an ~8.2:1 compression ratio**, making it a strong upgrade from stock pistons for engine rebuilds or performance builds.

Each piston is fully CNC machined and balanced for consistency, with features including deep valve reliefs, accumulator grooves, and double pin oilers to promote ring seal and lubrication in high-stress conditions. The set includes forged pistons, piston rings, and wrist pins, providing a complete solution for a rebuild or performance upgrade. CP Pistons are known for high-quality manufacturing, making this set suitable for high-output street, track, or rally applications on Subaru WRX STI, WRX, and Forester XT engines equipped with the EJ257 platform.