CP Piston & Ring Set for Subaru EJ257 WRX STi – Bore (99.5mm) – Size (Standard) – CR (8.2)

SKU: SC7420-4

CP Piston &amp. Ring Set for 2004-2021 Subaru Impreza WRX STI EJ257 – Bore 99.5mm Standard – CR 8.2

This CP piston and ring set SC7420-4 delivers forged reliability for Subaru EJ257 turbo engines in 2004-2021 Impreza WRX STI models. The 99.5mm standard bore and 8.2:1 compression ratio handle aggressive boost levels up to 40+ psi while ensuring durability in high-performance builds. Engine builders rely on this set for precise tolerances, weight matching, and consistent power in rally and drag applications.

Key Features

• Forged 2618-T6 Aluminum: Delivers high strength-to-weight ratio to handle extreme cylinder pressures in turbocharged EJ257 engines
• 8.2:1 Compression Ratio: Supports safe high-boost operation up to 40+ psi with lower detonation risk for reliable track performance
• Accumulator Grooves: Trap combustion residue to prevent ring flutter and maintain tight seal under high boost conditions
• Low-Friction Skirt Coating: Cuts drag, reduces operating temperatures, and prolongs piston life during aggressive shifts and launches
• Premium Rings and Pins Included: Pre-gapped rings with tool steel pins and clips for drop-in assembly and immediate competition use

Product Notes

• Set includes 4 pistons, rings, wrist pins, and clips balanced to OEM specifications
• Designed for stock 79mm stroke rods and crankshaft in EJ257 engines
• Ships ready for professional engine assembly with CNC-machined precision

Installation Notes

• Professional installation recommended.
• Hone cylinders to 99.5mm with CP-specific ra finish for optimal ring seating
• Compatible with OEM connecting rods and bearings

This Part Fits

Why Choose CP Pistons?

• Built in USA with motorsports heritage in rally and drag racing
• CNC-machined for exact bore fit and weight matching to OEM standards
• Engineered for Subaru EJ257 turbo platforms with proven high-boost handling

Frequently Asked Questions

• Q: Will SC7420-4 fit all EJ257 engines in 2004-2021 STI?
  A: Yes, direct fit for standard 99.5mm bore EJ257 in Impreza WRX STI models including Limited and Special Edition plus Legacy GT and Forester XT
• Q: What material are these pistons made from?
  A: Forged 2618-T6 aircraft-grade aluminum with phosphate coating and moly skirt finish for heat resistance and low friction
• Q: What warranty covers this piston set?
  A: Backed by CP Pistons limited warranty against manufacturing defects when installed by certified builders

Shipping & Handling

• Method: UPS Ground
• Availability: In stock – ships same or next business day
• Packaging: Foam-inserted box measuring 12 x 10 x 4 inches
• Weight: 5.8 lbs