Spec Clutch SJ40S Steel Flywheel SFI Certified High-Carbon Billet

The Spec Clutch SJ40S is a high-carbon billet steel flywheel engineered to deliver precision performance for high-demand driving and racing applications. CNC-machined to an extraordinary .001-inch tolerance — ten times tighter than the industry standard of .010 — this flywheel guarantees a perfectly flat clutch disc seating surface and true rotational balance for smooth, vibration-free engine revolutions.

Key Features:

• CNC machined to .001" tolerance — industry-leading precision for perfect balance and a flat friction surface
• High-carbon billet steel construction — optimized for medium-weight inertia applications across street and racing use
• Replaceable steel friction plate — friction-enhancing alloy steel specially formulated for optimum clutch bedding and holding power
• Rebuildable design — the friction plate is replaceable, extending the service life of the flywheel
• SFI certified — meets SFI safety standards for competitive and high-performance environments
• MOI (Moment of Inertia) optimized — engineered dimensions and weight tuned for maximum power transfer and performance output

The flywheel plays a critical role in clutch system performance, providing the friction surface for the clutch disc, managing rotational inertia to influence acceleration response, and maintaining dimensional accuracy at high RPM to eliminate power-robbing vibrations. Spec engineers each flywheel with specific weight and dimensional targets to deliver the ideal inertia balance for a given application — whether that's spirited street driving, autocross, drag racing, or road racing.

Spec flywheels are manufactured in the USA and backed by Spec's industry-leading torque guarantee. This steel unit is designed to pair with Spec clutch kits for a complete, performance-matched drivetrain upgrade.