ACT Xtreme Performance Street Sprung Clutch Kit w/ Monoloc - 2004-2021 Subaru WRX STI (SB10-XTSS)

The High-Torque Solution for Big-Power E85 & Upgraded Turbo STIs
The ACT Xtreme Performance Street Sprung Clutch Kit (SB10-XTSS) is built for the high-horsepower enthusiast who needs serious holding capacity but refuses to deal with the harsh engagement of a full race puck clutch. By combining ACT's highly tensioned Xtreme pressure plate with a premium full-face organic sprung hub disc, this single-disc kit punches well above its weight class. It safely supports a massive 598 ft-lbs of torque at the crank (a 68% increase over original equipment), making it the perfect match for heavily modified EJ257 builds running aggressive flex-fuel maps, rotated turbo kits, or demanding track setups.

Engineered to Dominate: Patented Monoloc Technology Included
Just like its heavy-duty sibling, the SB10-XTSS targets the weakest link in the Subaru 6-speed transmission: the pull-type wedge collar assembly. To prevent catastrophic failure or separation during brutal high-RPM gear slams, this kit includes ACT's patented Monoloc collar. Precision-crafted from hardened chrome-moly steel, the single-piece Monoloc safely replaces the failure-prone multi-piece OEM clip layout. This guarantees flawless alignment, reliable throwout bearing loading, and absolute security during competitive track runs or drag strip launches.

Every single kit is 100% clamp-load tested and dynamically computer-balanced to provide high-RPM reliability up to redline without vibrating.

• Massive 598 Ft-Lbs Capacity: Handles serious performance upgrades without immediately slipping or glazing the disc surfaces.
• Premium Organic Friction Material: Full-face sprung disc features high copper content for optimized thermal properties and steel-backed linings for bulletproof burst strength.
• Faster Shift Action: Designed with a shallower marcel wave structure to facilitate lightning-quick, positive high-RPM manual shifting.
• Patented Monoloc Defense: Eradicates the classic pull-type release bearing separation flaw right out of the box.

Technical Specifications:

• Part Number: SB10-XTSS
• Torque Capacity: 598 ft-lbs (At Crank)
• Torque Capacity Over OE: +68%
• Disc Style: Full Face Performance Organic Street Disc
• Hub Style: Spring-Centered / Sprung Hub
• Disc Diameter: 240mm (9.4 in.)
• Spline Count / Input Shaft: 24-Spline / 1.000 in.
• Pressure Plate Type: Xtreme
• Release Collar Upgrade: Patented ACT Monoloc Collar Included
• Product Total Weight: 18.2 lbs.

Fitment:

Engineered specifically for Pull-Type manual 6-speed transmission architectures.

• Subaru WRX STI (USDM & Canadian Markets): 2004–2021 (2.5L Turbo 6-Speed Manual)
  • Compatible with all trim levels: Base, Limited, Special Edition, Launch Edition, Series.HyperBlue, Type RA, S209, Sport, Sport-tech, Tsurugi Edition, and Kanrai Edition.
• Subaru Legacy GT spec.B: 2007, 2008, 2009 (2.5L Turbo 6-Speed Manual — Requires upgrading to an STI-style flywheel for height compatibility)
• Subaru Impreza WRX STI [JDM Models Only]: 2002, 2003, 2004, 2005 (2.0L Turbo 6-Speed Manual)

STI vs. WRX Selection: The SB10-XTSS configuration is purpose-built strictly for the specialized Pull-Type 6-speed gearboxes found in standard STI models. If you drive a standard USDM 5-speed or 6-speed push-type WRX (2006–2026+), this kit will not fit your transmission housing. You will instead need the push-type conversion kit, the ACT SB11-XTSS Clutch Kit, which includes its matching custom conversion flywheel.

The Nameless "Installation" Pro-Tip:

The Heavy-Duty Reality of an Xtreme Pressure Plate: Let's keep it completely real. The "XT" in this kit stands for Xtreme, meaning the diaphragm spring is heavily modified to maximize clamping power. As a result, your clutch pedal effort will be noticeably moderate-to-heavy compared to the factory stock setup. If your car is a dedicated street daily driver that constantly encounters stop-and-go morning traffic, your left leg might prefer the lighter ACT SB10-HDSS package. However, if you are regularly making track pulls, launching on sticky tires, or targeting more than 450 whp, the XT layout is absolute gold armor.

What's in the Box? This package includes the Xtreme Pressure Plate, Performance Street Organic Disc, standard release bearing, an alignment tool, the ACT PB1004 Pilot Bearing, and your patented Monoloc wedge collar.

Remember, this kit does not include a flywheel out of the box. Be sure to completely resurface your factory flywheel or make a smart performance upgrade by dropping in a lightweight chromoly ACT Streetlite (600235) or full-race ACT Prolite (600240) unit while the transmission is dropped!