HKS Low Compression Stroker Replacement Pistons

2013–2020 Subaru BRZ / 2013–2016 Scion FR-S / 2017–2020 Toyota 86 2.1L FA20

21003-AT004

Overview:

The HKS Low Compression Stroker Replacement Pistons are engineered specifically for the Subaru BRZ, Scion FR-S, and Toyota 86 equipped with the 2.1L FA20 stroker upgrade. Designed as a direct replacement for the pistons in the HKS 21004-AT003 and 21004-AT004 stroker kits, these pistons are not compatible with rods or crankshafts outside the HKS 2.1L capacity upgrade.

Built for enthusiasts seeking enhanced durability and the ability to run higher boost levels, these pistons optimize compression ratios to support increased power output while maintaining reliability. Whether you are upgrading for spirited street driving or track use, these pistons provide a solid foundation for your engine build.

Key Features:

These replacement pistons incorporate advanced materials and design to meet the demands of high-performance FA20 stroker engines:

• Specially forged raw materials selected to improve durability under high stress conditions
• Recessed piston design accommodates high-lift HKS camshafts for optimal valve clearance
• Compression ratio optimized through extensive strength analysis and testing to allow flexible tuning and high boost capability
• 3D-designed piston crown tailored for the stock direct injection system and enhanced tumble flow for efficient combustion
• Compatibility with varying compression ratios depending on the head gasket used
• Molybdenum coating on piston skirts reduces friction and wear for improved longevity
• Maintains the factory 86mm piston bore to preserve block strength and eliminate the need for boring, honing, or sleeves
• Cost-effective installation by retaining stock bore dimensions

Construction & Design:

The pistons are crafted from high-quality forged materials to withstand the increased loads of a stroked 2.1L FA20 engine. The recessed design ensures compatibility with HKS high-lift camshafts, preventing valve-to-piston interference. The piston crown features a sophisticated 3D shape that complements the stock direct injection system, promoting efficient air-fuel mixing and combustion.

The molybdenum coating on the piston skirts reduces friction against the cylinder walls, enhancing wear resistance and contributing to smoother engine operation. By retaining the factory bore size, the pistons allow for a straightforward installation without the need for additional machining, preserving the structural integrity of the engine block.

Installation & Fitment:

This piston kit is intended exclusively as a replacement for the pistons included in the HKS 2.1L FA20 stroker kits (part numbers 21004-AT003 and 21004-AT004). It is not compatible with other rods or crankshafts outside of the HKS 2.1L upgrade.

Installation is simplified by the retention of the stock 86mm bore, eliminating the need for boring, honing, or installing sleeves. This reduces labor time and cost, making it an efficient upgrade for those maintaining or refreshing their stroker build.

• Direct replacement pistons for HKS 2.1L FA20 stroker kits
• No machining of the engine block required
• Compatible with factory bore size to maintain block strength
• Designed for use with HKS rods and crankshaft in the 2.1L stroker configuration

What's Included:

• Set of forged low compression replacement pistons designed for the HKS 2.1L FA20 stroker kit

Ideal For:

This piston kit is ideal for Subaru BRZ, Scion FR-S, and Toyota 86 owners who have upgraded to or plan to upgrade to the HKS 2.1L stroker kit and require durable, high-performance pistons capable of handling increased boost and power levels. It suits enthusiasts focused on maximizing engine strength and reliability while maintaining cost-effective installation.