Engines and Components› Pistons and Piston Rings

HKS

HKS PISTON KIT FA20 2.1L LOW COMP

$1,190.00

SKU: H005 21003-AT004

Special Order
Special Order
Ships in 4–6 weeks
Free Shipping over $200
$100 Minimum Order
Non-Returnable Item

Overview

The HKS Low Compression Stroker Replacement Pistons are engineered for the Subaru BRZ, Scion FR-S, and Toyota 86 equipped with the 2.1L FA20 stroker upgrade. These forged pistons are designed as a direct replacement for the pistons included in HKS 21004-AT003 and 21004-AT004 stroker kits. They feature specially forged raw materials for durability under high stress, a recessed design for high-lift HKS camshafts, and an optimized compression ratio for flexible tuning and high boost. The 3D-designed piston crown is tailored for the stock direct injection system, and a molybdenum coating on the skirts reduces friction. These pistons maintain the factory 86mm bore, simplifying installation by eliminating the need for boring, honing, or sleeves.
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Part #: 21003-AT004

Product descriptions are provided by our supplier partners and may not always be perfectly accurate. Not sure this fits? or call (760) 282-4645 and we’ll verify before you order.

Fitment

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Specifications

BrandHKS
Part NumberH005 21003-AT004

Videos

FA20 Engine Rebuild Part 2 Piston Assembly FRS/BRZ/FT86

FA20 Engine Rebuild Part 2 Piston Assembly FRS/BRZ/FT86

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Returns & Fitment

Built for enthusiasts. Every order is backed by our 30 day return window on eligible items. Unused and uninstalled products may be returned with approved RMA and no restocking fees when received in new condition. Orders placed through the MOTORMIA app with a complete build qualify for our Fitment Guarantee — free return shipping if the part doesn’t fit your exact setup. The guarantee covers fit only; installation must follow manufacturer instructions, and we recommend a qualified shop for parts marked Difficulty 4–5.

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Shipping

Orders are processed in 1–3 business days. In stock parts ship promptly from our partner network. Special-order items either aren’t currently stocked or are built to your spec — expect 4–6 weeks. If a part goes on backorder while your order is in the queue, we’ll reach out and work through discounted alternatives together.

Free shipping over $200 in the continental US. Alaska, Hawaii, U.S. territories (Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, and the Northern Mariana Islands), and international orders carry surcharges — most appear at checkout. Some exceptions (LTL freight, or suppliers who quote freight only after we place the order) won’t. In those cases we’ll reach out with the exact charge before your order moves forward.

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