JE Ultra Series Forged Piston Kit for Subaru STI EJ257 99.75mm 9.5:1 - 361331

JE Pistons | Ultra Series | Subaru EJ257 STI | 99.75mm Forged Pistons | 9.5:1 Compression | 2618 Aluminum | Set of 4

Building a Subaru STI that can handle serious turbocharged performance without relying on factory-style pistons? The JE Ultra Series Forged Piston Kit, part number 361331, is designed for EJ257 owners who want to put together a stronger, more capable short block. Whether you're rebuilding an engine after piston damage, stepping up to a larger turbocharger, or preparing your Subaru for demanding street and track use, these American-made forged pistons bring competition-focused technology to the heart of your engine.

This kit uses JE's premium Aligned Grain Flow forging process and high-strength 2618 aluminum, paired with a 99.75mm bore and 9.5:1 nominal compression ratio. The higher-compression configuration is a useful option for builders seeking responsive turbocharged performance while retaining the strength-oriented features of the Ultra Series. Thermal-barrier crown coating, lateral gas ports, accumulator grooves, and coated skirts help address the heat, ring sealing, and friction challenges that come with demanding engine builds. Heavy-duty 9310 steel wrist pins and premium piston rings complete the four-piston package.

Key Features & Specifications:

Kit Includes:

• 4 x JE Ultra Series 2618 Forged Aluminum FSR Pistons

• JE Pro Seal Premium Piston Ring Set

• 4 x 9310 Nickel Carbon Steel Alloy Wrist Pins

• Wrist Pin Retaining Locks

About the JE Ultra Series Subaru EJ257 Pistons

A Serious Upgrade for the Subaru STI

The EJ257 is a favorite among Subaru enthusiasts for its turbocharged performance potential, but increasing boost and power also raises the demands on the engine's internal components. When it's time to rebuild a damaged STI engine or assemble a fresh performance short block, choosing a piston package designed around those demands is an important investment.

JE's Ultra Series is built for enthusiasts who want the company's advanced piston technology without ordering a completely custom set. The 9.5:1 nominal compression configuration makes these pistons an option for builders seeking a different balance of engine response and turbocharged performance than lower-compression EJ257 setups.

The pistons are forged from 2618 aluminum using JE's proprietary Aligned Grain Flow technology, which is engineered to increase tensile strength for demanding power-adder applications.

Lightweight FSR Forging and Advanced Ring Sealing

JE's Forged Side Relief design reduces piston skirt width to minimize friction and unnecessary reciprocating weight. It also accommodates a shorter wrist pin, helping create an efficient forged piston assembly.

The accumulator groove provides additional volume between the top and second compression rings, reducing trapped gas pressure that can contribute to ring flutter.

Lateral gas ports provide a path for combustion pressure to reach the back of the top compression ring. Under high-load conditions, this pressure helps promote ring sealing, making the design particularly relevant to engines operating at elevated cylinder pressures.

Thermal Protection and Reduced Friction

The Ultra Series thermal crown coating acts as a barrier against heat transfer into the piston body. By reflecting heat toward the combustion chamber, the coating is designed to help manage piston temperatures during demanding operation.

A skirt coating helps reduce friction and wear between the piston skirts and cylinder walls while also reducing operating noise.

JE also uses a smooth crown finish to remove sharp edges around the piston crown and valve relief areas, helping reduce potential hot spots and stress concentrations.

Premium Wrist Pins and Precision Assembly

The included wrist pins are manufactured from 9310 nickel carbon steel alloy with a 0.210-inch wall thickness. These upgraded pins are selected for the demanding operating conditions associated with high-performance engine builds.

JE precision-hones the pin bores to achieve controlled wrist pin clearance. Typical pin-fit clearance ranges from 0.0003 to 0.0010 inches, although final measurements must follow the actual parts and engine assembly specifications.

Combined with the included JE Pro Seal piston rings and retaining locks, this kit provides the piston components needed for a carefully engineered EJ257 short block.

For Subaru owners who want a high-compression forged piston package with premium thermal protection, advanced ring-sealing technology, and strong wrist pin construction, JE Ultra Series 361331 offers a performance-focused solution.

Fitment & Installation Notes:

• Subaru EJ257 STI: Designed for the 2.5L turbocharged EJ257 engine and STI cylinder head configuration.

• Other EJ25 Applications: Verify cylinder head design, combustion chamber volume, connecting rods, and piston geometry before considering this kit for other EJ-series engines.

• Required Finished Bore: 99.75mm.

• Overbore: +0.25mm compared with the standard 99.50mm EJ257 bore.

• Compression Ratio: Nominal 9.5:1 based on the specified EJ257 engine geometry and reference combustion chamber volume. Actual assembled compression may vary.

• Piston Configuration: -7.30cc dished crown with 1.209-inch compression height.

• Engine Stroke: Designed around the standard 79mm stroke.

• Connecting Rod Length: Approximately 130.5mm.

• Wrist Pin Diameter: 0.905 in.

• Cylinder Machining: Measure the actual pistons and finish the bores to JE's specified piston-to-wall clearance.

• Ring Installation: Measure and set piston ring end gaps for the intended fuel, boost pressure, and operating conditions.

• Piston-to-Valve Clearance: Verify clearance during assembly, particularly with aftermarket camshafts, modified cylinder heads, or altered valve timing.

• Connecting Rod Compatibility: Confirm rod length, small-end dimensions, and wrist pin fit.

• Engine Calibration: Fuel delivery, ignition timing, boost control, and ECU tuning must match the completed engine configuration.

• Performance Application: Designed for properly engineered turbocharged street, track, and competition engines.

• Horsepower Rating: No fixed horsepower limit is specified for part 361331. Engine capability depends on the complete assembly, machining, supporting components, and calibration.

The JE Ultra Series 361331 piston kit combines American-made forged 2618 construction, a 9.5:1 compression configuration, advanced ring-sealing technology, thermal protection, and premium wrist pins for demanding Subaru EJ257 performance builds.