JE Pistons JG4904-3937 Piston Ring Set for Subaru EJ257 EJ20 Engines

Vehicle Fitment

• Subaru EJ257 block with EJ20 head configuration
• Used in various Subaru WRX and STI engine builds (fitment must be verified)
• File-fit application, not direct OE drop-in

Features

• High-performance Pro Seal piston ring construction
• Top ring made of carbon steel with nitride treatment
• Second ring features iron phosphate coating for reduced friction
• Oil ring uses low-tension chrome carbon steel for improved oil control
• File-fit design allows precise cylinder wall sealing
• Supports turbocharged and high-compression engine builds
• Reduced blow-by and optimized combustion efficiency
• Ideal for custom and competition Subaru EJ engine builds

Specifications

• Bore size: 3.937 in (100.00 mm)
• Top ring thickness: 1.20 mm (0.0472 in)
• Second ring thickness: 1.20 mm (0.0472 in)
• Oil ring thickness: 2.50 mm (0.0984 in)
• Material: Carbon steel, iron phosphate, chrome finish
• Configuration: 3-ring set per cylinder
• Application: 4-cylinder Subaru EJ engines
• Design type: File-fit performance ring set

Included Components

• 4x Top rings
• 4x Second rings
• 4x Oil control ring assemblies
• 1x Installation instruction sheet

Product Description

The JE Pistons JG4904-3937 piston ring set is engineered for high-output Subaru EJ-series engines, specifically those utilizing an EJ257 block mated to EJ20 heads. Featuring premium Pro Seal technology, these file-fit rings deliver exceptional sealing and durability under high boost, nitrous, or high-compression conditions.

Each ring set includes precision-machined components designed to withstand extreme cylinder pressures while maintaining excellent oil control. The nitride top ring enhances wear resistance, the iron phosphate second ring minimizes friction, and the low-tension chrome oil ring reduces drag.

Ideal for professional engine builders and serious tuners, this kit provides optimal performance for custom Subaru EJ configurations. Fitment should always be confirmed against block and head specifications before installation.