JE Pistons FSR Forged Piston Kit Subaru WRX STI (EJ20/EJ25) 100.00mm Bore -15.10cc Dish

JE Pistons FSR Forged Piston Kit - Subaru WRX STI (EJ20/EJ25) - 100.00mm Bore, -15.10cc Dish

When you're building a serious EJ-powered Subaru, the pistons are one area where you simply cannot cut corners. JE Pistons brings over 75 years of forged piston development to this FSR series kit, engineered and machined entirely in the USA from 2618 aluminium alloy — the material of choice for high output and forced induction applications where thermal cycling and detonation resistance matter most. This isn't an off-the-shelf compromise; it's a purpose-built forging designed around the specific demands of the Subaru WRX STI EJ20/EJ25 engine family.

This listing covers the JE Pistons FSR forged piston kit for the Subaru WRX STI running the EJ20 or EJ25 engine (cylinder head: EJ257 STI), at a finished bore diameter of 100.00mm with a -15.10cc dish piston head. Please confirm your bore size and target compression ratio before ordering.

Note: These pistons are supplied at 100.00mm bore. Your machine shop must confirm final bore sizing and piston-to-wall clearance to suit your specific build. Compression ratio will vary depending on your head gasket thickness, deck height, and chamber volume — use a compression calculator with your engine's exact dimensions before purchase.

Key Features

• Forged from 2618 aluminium alloy for exceptional strength and resilience under high heat and cylinder pressure
• FSR (Forged Side Relief) design reduces skirt width, lowering friction and parasitic power loss while trimming overall piston weight
• Shorter wrist pin enabled by the FSR forging design further reduces reciprocating mass
• Skirt coating reduces friction and wear against cylinder walls, with the added benefit of quieter operation
• Accumulator groove (where applicable) relieves combustion gas pressure from behind the top ring, reducing ring flutter and improving ring seal consistency
• Engineered specifically for the EJ257 STI cylinder head geometry, including valve pocket profiling
• Kit includes four pistons, wrist pins, retaining locks, and JE Pro Seal premium piston rings
• 100% designed, forged, and machined in the USA

Specifications

• Piston series: JE FSR
• Material: 2618 aluminium alloy
• Bore diameter: 100.00mm
• Piston head type: Dish
• Piston volume: -15.10cc
• Compression height: 30.73mm (1.210 in)
• Average piston weight: 391g
• Quantity: 4 pistons
• Top compression ring thickness: 1.22mm (0.0480 in)
• Second compression ring thickness: 1.22mm (0.0480 in)
• Oil ring thickness: 2.53mm (0.0995 in)
• Wrist pin outer diameter: 22.99mm (0.905 in)
• Wrist pin length: 57.15mm (2.250 in)
• Wrist pin wall thickness: 4.57mm (0.180 in)
• Intake valve pocket depth: 9.40mm (0.370 in)
• Intake valve pocket diameter: 57.53mm (2.265 in)
• Intake valve angle: 21°
• Exhaust valve pocket diameter: 47.50mm (1.870 in)
• Exhaust valve angle: 21°
• Ring set included: Yes (JE Pro Seal)
• Cylinder head: EJ257 STI

Fitment details, compatible engine codes, and any additional application notes are provided in the tabs above. Please confirm your engine variant, bore size, and build specifications before ordering.

Not sure if this kit suits your build? Contact our team at sales@chicaneaustralia.com.au for expert advice.