ACT’s Heavy Duty and Xtreme pressure plates differ in clamp load and pedal feel. The Heavy Duty plate raises clamp load over stock while keeping light to moderate pedal effort, which suits daily-driven cars with bolt-ons and moderate power. The Xtreme plate clamps harder for more torque capacity but needs moderate to heavy pedal effort. On the 2006-2021 WRX kits we list, ACT rates the Heavy Duty kit at 449 ft-lb and the Xtreme kit at 510 ft-lb, both with the same organic Performance Street sprung disc.
ACT Heavy Duty vs Xtreme (WRX kits we list)
| Heavy Duty (SB11-HDSS) | Xtreme (SB11-XTSS) | |
|---|---|---|
| Torque capacity (ACT rating) | 449 ft-lb, 39% over stock | 510 ft-lb, 51% over stock |
| Pedal effort (ACT rating) | Light to moderate | Moderate to heavy |
| Disc | Organic Performance Street sprung | Organic Performance Street sprung |
| Flywheel | Streetlite | Streetlite |
| Price | $1,204.00 | $1,254.00 |
Which should you choose?
- Heavy Duty if the car is driven daily, sits in traffic, and makes moderate power over stock. The lighter pedal is much easier to live with.
- Xtreme if you have added substantial torque, launch hard, or have slipped a Heavy Duty clutch, and you accept a heavier pedal.
- Choose by torque at the wheels with some margin, not by peak horsepower alone.
What the pressure plate does
The pressure plate squeezes the disc against the flywheel. More clamp load means more torque before slipping, but also a stiffer pedal and more load on the release bearing and clutch hydraulics. The disc material decides how smoothly that grip comes in; see organic vs ceramic clutch and Stage 1 vs Stage 2 vs Stage 3.
Supporting parts
A heavier pressure plate puts more load on the clutch hydraulics. Bleed the system thoroughly, check the master and slave cylinders, and consider a stronger pedal assist or bushings only if the maker recommends them. A failing hydraulic part can feel like a clutch that will not release; see clutch master cylinder symptoms.
Lightweight flywheel
Both WRX kits include ACT’s Streetlite flywheel, which lets the engine rev more quickly. It can add a little gear rattle at idle; ACT rates both kits from stock-like to mild rattle.
Other ACT Heavy Duty kits we list
- ACT HC10-HDSS for Civic 1.5T and Si: $1,242.00
- ACT ME3-HDSS for Evo X: $915.00
- ACT ME2-HDSS for Evo 8 and 9: $853.00
The kits compared above
- ACT HD Performance Street Sprung Clutch Kit, WRX (SB11-HDSS): $1,204.00
- ACT Xtreme Clutch Kit with Streetlite Flywheel, WRX (SB11-XTSS): $1,254.00
After installing either, follow the break-in procedure; see clutch break-in.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.