HKS 21003-AM002 4G63 2.3L Forged Piston Kit 85.5mm Stroker Upgrade

The HKS 21003-AM002 is a forged piston kit designed as the Step 1 component of HKS's 4G63 Capacity Upgrade Kit, upgrading the engine displacement from the stock 1,997cc to 2,231cc. This precision-engineered kit is purpose-built for high-performance and motorsport applications, delivering a significant increase in torque that enables the use of larger-capacity turbochargers.

Each piston features a nickel-plated top for increased durability and an Ober-coated skirt to improve anti-knock properties and reduce friction. The oversized 85.5mm bore requires cylinder boring and honing prior to installation, but no block clearance modifications are necessary for the larger stroke crankshaft.

Kit Contents:

• HKS forged aluminum pistons (85.5mm bore)
• Piston rings
• Wrist pins (22.0mm pin bore)
• Retaining clips

Key Specifications:

• Piston Bore: 85.5mm
• Pin Bore: 22.0mm
• Displacement: 2,204.7cc
• Piston Top Coating: Nickel Plating
• Piston Skirt Coating: Ober Coating

Installation Notes:

• Cylinder boring and honing required (0.5mm oversized pistons)
• No block clearance modifications required for larger stroke crankshaft

All HKS engine components are manufactured in Japan under strict quality supervision, from processing and inspection through final packaging. This piston kit is the Step 1 forged piston-only option; a complete Step 2 full kit (including forged crankshaft and H-beam connecting rods) is also available separately.