Wilwood - Forged Billet Superlite 4/ST Caliper with Thermlock Pistons

Wilwood – Forged Billet Superlite 4/ST Brake Caliper with Thermlock® Pistons (FSLI4 / FSLI4-ST)

The Wilwood Forged Billet Superlite Internal 4/ST (FSLI4-ST) brake caliper is designed for sustained, high-temperature racing applications where strength, weight reduction, and consistent pad wear are critical. These calipers utilize differential bore pistons to compensate for leading-edge loading and temperature variation across the pad face, significantly reducing pad taper wear.

ST models are equipped with Thermlock® pistons, which block heat transfer from the brake pads and reduce temperatures in the caliper body, seals, and brake fluid by up to 25% compared to standard stainless pistons.

These calipers feature internal fluid ports, eliminating external crossover tubes and the potential failures associated with them. Dual bleed screw assemblies allow the caliper to be mounted in leading or trailing positions.

With an assembled weight of just 4.4 lbs, the FSLI4 calipers deliver exceptional strength with minimal deflection thanks to Wilwood’s stress-flow forged premium aluminum billet construction.

Features & Benefits

• Differential bore pistons – Reduce pad taper wear
• Thermlock® pistons (ST models) – Up to 25% heat reduction
• Forged billet construction – High strength, low weight
• Ultra-lightweight – Approx. 4.4 lbs assembled
• Internal fluid ports – No external crossover tubes
• Dual bleed screw design – Leading or trailing mounting
• Closed-end bridge design – Reduced deflection

Caliper Specifications

• Caliper Type: Forged Superlite Internal 4 (FSLI4 / FSLI4-ST)
• Pistons: Staggered differential bore
• Piston Option: Thermlock® (ST models)
• Pad Style: 7420 XL Superlite
• Mounting Bolt Pattern: 3.50"
• Material: Stress-flow forged premium aluminum alloy
• Weight: Approx. 4.4 lbs assembled
• Application: Dirt & asphalt ovals, road course, rally, off-road