HKS 21005-AN024 TYPE-LF Low Friction Piston Ring Set 87mm 4-Cylinder

The HKS 21005-AN024 TYPE-LF Piston Ring Set is an updated, low-friction piston ring set designed for 87.0 mm (Ø87.0 mm) bore, 4-cylinder applications. This set incorporates HKS's latest ring technology across all three ring positions — top ring, second ring, and oil ring — delivering improved sealing performance, reduced blow-by, and lower frictional losses compared to previous-generation HKS piston ring designs. Designed as a direct replacement for use with compatible HKS forged piston kits.

Top Ring:

• Redesigned to reduce blow-by gas under both cold-start and high-temperature operating conditions
• Gas passage area at the ring end gap reduced by approximately 27% at room temperature
• Higher coefficient of thermal expansion material further reduces end gap by approximately 88% at operating temperature
• New material provides approximately 37% higher thermal conductivity, improving heat transfer away from the piston and reducing ring groove wear
• Reduced ring tension minimizes frictional losses; optimized surface treatment and coating thickness improve initial seating, durability, and service life

Second Ring:

• Designed to stabilize the top ring and improve overall sealing performance
• Ring end gap increased by approximately 25%, reducing pressure in the second land area between the top and second rings
• Lowered second-land pressure suppresses top ring flutter during high-speed operation, supporting stable ring movement and improved sealing
• Ring tension reduced by approximately 18% compared to the previous design, contributing to lower friction

Oil Ring:

• Redesigned from the previous two-piece construction to a new three-piece design
• Ring tension reduced by approximately 10%, resulting in a significant reduction in frictional losses

Key Specifications:

• HKS Part Number: 21005-AN024
• UPC: 4957266632413
• Bore Diameter: 87.0 mm
• Configuration: 4-Cylinder set
• Ring Type: TYPE-LF (Low Friction)
• Oil Ring Design: 3-Piece
• Not CARB legal — not for sale in California

The HKS 21005-AN024 TYPE-LF piston ring set represents HKS's commitment to incorporating the latest internal combustion engine technology into their performance engine components. Sold as a complete ring set for one engine. Pistons not included.