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Building a Subaru EJ257 that can handle more than a typical factory-style rebuild? The JE Pistons Forged Piston Kit, part number 296348, gives your STI engine a performance-focused foundation for demanding street, track, and motorsport applications. Manufactured in the USA from 2618 forged aluminum, these pistons feature JE's lightweight Forged Side Relief (FSR) design, a -17cc dish, precision pin fit, and friction-reducing skirt coating. Whether you're refreshing an EJ257 after piston damage or assembling a turbocharged short block for future upgrades, this matched application-specific piston package provides the strength, sealing features, and installation components needed for a carefully engineered performance engine build.
Key Features & Specifications:
| Specification | Details |
|---|---|
| Brand | JE Pistons |
| Part Number | 296348 |
| Piston Series | JE Pistons |
| Engine Application | Subaru EJ257 STI |
| Cylinder Head | EJ257 STI |
| Piston Material | Forged 2618 Aluminum |
| Forging Type | FSR (Forged Side Relief) |
| Bore Diameter | 99.75mm |
| Piston Head Type | Dish |
| Piston Volume | -17.00cc |
| Compression Height | 1.209 in. |
| Average Piston Weight | 405g |
| Piston Quantity | 4 |
| Top Compression Ring Thickness | 0.0480 in. |
| Second Compression Ring Thickness | 0.0480 in. |
| Oil Ring Thickness | 0.0995 in. |
| Top Ring Groove Width | 0.04800 in. |
| Second Ring Groove Width | 0.04800 in. |
| Oil Ring Groove Width | 0.09950 in. |
| Wrist Pin Outer Diameter | 0.905 in. |
| Wrist Pin Length | 2.250 in. |
| Wrist Pin Wall Thickness | 0.180 in. |
| Intake Valve Relief Depth | 0.165 in. |
| Intake Valve Relief Diameter | 1.550 in. |
| Intake Valve Relief Angle | 20° |
| Exhaust Valve Relief Depth | 0.165 in. |
| Exhaust Valve Relief Diameter | 1.550 in. |
| Exhaust Valve Relief Angle | 20° |
| Accumulator Groove | Yes |
| Precision Pin Fit | Yes |
| Skirt Coating | Yes |
| Ring Set Included | Yes, JE Pro Seal |
| Wrist Pins Included | Yes |
| Wrist Pin Locks Included | Yes |
| Manufacturing Location | USA |
Kit Includes:
4 x JE Pistons 2618 Forged Aluminum FSR Pistons
JE Pro Seal Premium Piston Ring Set
Wrist Pins
Wrist Pin Locks
The Subaru EJ257 has earned its reputation as a capable turbocharged performance platform, but rebuilding one correctly means choosing internal components suited to the intended power level and driving conditions. JE's 2618 forged aluminum pistons provide a durable, ductile foundation for engines exposed to elevated combustion pressures and demanding use.
JE's proprietary Forged Side Relief (FSR) design uses a reduced skirt width to minimize friction and unnecessary weight. The design also accommodates a shorter wrist pin, helping reduce reciprocating mass without abandoning the structural features needed for a performance piston.
This particular set includes three important enhancements:
Accumulator Groove: A precisely machined groove between the top and second piston rings provides additional space for blow-by gases. This helps reduce pressure buildup between the rings, supporting improved top-ring sealing and reducing ring flutter under high cylinder pressures.
Precision Pin Fit: The wrist pin bores are precision-honed for controlled pin clearance. JE specifies typical pin-to-bore clearances of 0.0003 to 0.0010 inches, although the final assembly must follow the supplied piston measurements and engine-builder requirements.
Skirt Coat: A specialized skirt coating is designed to reduce friction and wear between the piston skirts and cylinder walls while helping limit operating noise.
Together with the included JE Pro Seal rings, wrist pins, and locks, these features make 296348 a compelling choice for enthusiasts putting together a properly machined EJ257 short block for spirited street driving, track use, or more demanding turbocharged applications.
Fitment & Installation Notes:
Subaru EJ257 STI: Designed specifically for EJ257 STI cylinder head and engine applications.
Bore Requirement: 99.75mm finished cylinder bore.
Piston Configuration: -17.00cc dished crown with 1.209-inch compression height.
Compression Ratio: Depends on cylinder head chamber volume, head gasket dimensions, deck height, and engine configuration; no fixed ratio is specified for this kit.
Engine Machining: Verify cylinder bore condition, piston-to-wall clearance, and finished bore dimensions before installation.
Piston Clearance: Follow JE's installation specifications for 2618 forged aluminum pistons.
Ring Preparation: Measure and set ring end gaps for the intended engine application and operating conditions.
Valve Clearance: Confirm piston-to-valve clearance during engine assembly, particularly when using aftermarket camshafts, modified heads, or nonstandard timing components.
Wrist Pin Installation: Verify final pin fit and connecting rod compatibility.
Engine Tuning: Appropriate fuel delivery, ignition calibration, and boost control are essential for reliable operation of a modified EJ257.
Horsepower Rating: No specific horsepower limit is established for part 296348. Engine durability depends on the complete build, machining, tune, and operating conditions.
The JE Pistons 296348 Subaru EJ257 forged piston kit combines American-made 2618 aluminum construction, lightweight FSR forging, a -17cc dished crown, accumulator grooves, precision pin fit, and skirt coating for a serious four-cylinder performance engine build.
