Wiseco K598M9955AP Subaru EJ257 Forged Piston Set 99.55mm Bore -19cc Dish

The Wiseco K598M9955AP is a Professional Series forged piston set designed for the Subaru EJ257 engine, featuring a 99.55 mm bore and a -19cc dish crown for optimized compression tuning in boosted applications.

Wiseco engineered these pistons with a dish crown profile to optimize squish and quench during the compression-combustion cycle, promoting resistance to detonation and pre-ignition — critical factors in high-boost turbocharged EJ257 builds. The -19cc dish volume gives builders precise control over final compression ratio when paired with appropriate head gaskets and combustion chamber volumes.

Key Features:

• 2618 High-Strength Aluminum Alloy — Forged and machined in the USA for improved tensile strength in boosted applications
• ArmorGlide® Skirt Coating — Seizure-resistant coating reduces operating friction and noise while minimizing skirt and cylinder wear
• Accumulator Groove — Helps maintain consistent ring seal and power output under high boost
• 99.55 mm Bore Diameter — Oversize bore for engines that have been machined; check your block bore specification before ordering
• 30.70 mm Compression Height — Precision-machined for proper deck clearance
• 0.9055 in. Wrist Pin Diameter — Offset pin design matches OEM specification for quietest operation
• 4-Valve Dish Crown (-19cc) — Engineered for multi-valve EJ257 cylinder heads with compatible valve pocket geometry
• Lightening Operations — Non-critical areas machined to reduce reciprocating mass while maintaining structural integrity

Included in Kit:

• Premium ring sets — 1mm x 1.2mm x 2.8mm XX configuration with stainless steel gas nitrided top ring, cast iron Napier hook second ring, and flex-vent oil ring with gas nitrided scraper rails
• Wrist pins and retaining clips

The Wiseco K598M9955AP piston kit is engineered, forged, and machined at Wiseco's Mentor, Ohio manufacturing facility, making it a top choice for EJ257 engine rebuilds where durability and performance are non-negotiable.