JE Ultra Series Forged Piston Kit for 2004-2017 Subaru STI EJ257 99.75mm - 361328

JE Pistons | Ultra Series | Subaru STI EJ257 | 99.75mm | 8.5:1 Compression | Forged 2618 | FSR | Set of 4

Building an EJ257 that can stand up to serious boost and demanding track use? The JE Pistons Ultra Series Forged Piston Kit, part number 361328, gives Subaru STI owners a premium foundation for a properly engineered performance engine. Whether you're rebuilding an EJ25 after piston or ring-land damage or assembling a high-output turbocharged short block, these American-made 2618 forged pistons are designed for the elevated cylinder pressures of power-adder applications.

Unlike a basic replacement piston, the Ultra Series combines JE's Aligned Grain Flow forging technology with advanced features that address piston strength, heat management, ring sealing, and friction. This kit features a 99.75mm bore, an 8.5:1 nominal compression ratio, thermal-barrier crown coating, lateral gas ports, skirt coating, and upgraded 9310 steel wrist pins. It's a serious piston package for enthusiasts who want to build their Subaru engine around performance rather than simply return it to stock.

Key Features & Specifications:

Kit Includes:

• 4 x JE Ultra Series Forged 2618 Aluminum Pistons

• 1 x JE Pro Seal Piston Ring Set

• 4 x 9310 Nickel Carbon Steel Wrist Pins

• Wrist Pin Retaining Locks

About the JE Ultra Series Subaru EJ257 Pistons

The Subaru EJ257 is an excellent platform for turbocharged performance, but increased boost and cylinder pressure demand careful attention to engine internals. JE's Ultra Series is designed for builders pursuing more demanding applications, from aggressive street setups to dedicated competition engines.

Aligned Grain Flow Forging

JE's proprietary Aligned Grain Flow forging technology is engineered to improve tensile strength in areas exposed to high mechanical stress. Combined with 2618 aluminum alloy and the lightweight FSR design, it creates a strong piston structure suited to high-cylinder-pressure applications.

FSR construction also reduces skirt width and accommodates shorter wrist pins, helping reduce friction and unnecessary reciprocating weight.

Accumulator Grooves and Lateral Gas Ports

High combustion pressure can create challenges for piston ring sealing, especially in heavily boosted engines.

The accumulator groove provides additional volume between the top and second compression rings, helping reduce trapped gas pressure and ring flutter.

Lateral gas ports allow combustion pressure to reach the back of the top ring, helping improve ring sealing during high-load operation. Together, these features target consistent cylinder pressure control when the engine is working hard.

Thermal Crown and Skirt Coatings

The Ultra Series thermal crown coating creates a barrier that reduces heat transfer into the piston while reflecting heat toward the combustion chamber. This helps manage the thermal demands of high-output engine operation.

JE's skirt coating is designed to reduce friction and wear between the piston skirt and cylinder wall. It can also help reduce operating noise, an especially useful feature when building an engine with 2618 forged pistons.

Upgraded Wrist Pins and Precision Pin Fit

This kit uses 9310 nickel carbon steel alloy wrist pins with a 0.210-inch wall thickness for demanding performance applications.

The pin bores are precision-honed to achieve controlled clearance between the pins and pistons. JE specifies typical pin-fit clearances ranging from 0.0003 to 0.0010 inches, with final measurements determined during engine assembly.

Fitment & Installation Notes

• 2004-2017 Subaru Impreza WRX STI / WRX STI: EJ257 2.5L turbocharged engine applications.

• Engine Family: Subaru EJ Series, specifically designed for the EJ257 STI cylinder head configuration.

• Required Finished Bore: 99.75mm, representing a 0.25mm overbore compared with the standard 99.50mm bore.

• Compression Ratio: Nominal 8.5:1 with the specified EJ257 engine geometry. Actual assembled compression depends on combustion chamber volume, head gasket thickness, piston deck height, and other engine measurements.

• Piston Configuration: -16.90cc dished crown with 1.209-inch compression height.

• Engine Machining: Cylinders must be measured and finished for the correct piston-to-wall clearance. The stated bore size alone is not an installation clearance specification.

• Ring Installation: Measure and set the supplied piston rings' end gaps for the intended boost level, fuel, and operating conditions.

• Valve Clearance: Verify piston-to-valve clearance during assembly, especially with aftermarket camshafts or modified cylinder heads.

• Connecting Rod Compatibility: Verify rod specifications and the 0.905-inch wrist pin requirement.

• Intended Use: Properly engineered turbocharged street, track, and competition engine builds.

• Horsepower Rating: No fixed horsepower limit is specified for this kit. Safe operating power depends on the complete engine build, machining, supporting components, and tuning.

For the enthusiast rebuilding a damaged EJ257 or building a stronger Subaru STI engine for increased boost, the JE Ultra Series 361328 offers premium forged construction and carefully engineered ring-sealing, heat-management, and friction-control features in a complete four-piston package.