The ACT HD Street Sprung Clutch Kit covers a large portion of STI builds well, but it has a ceiling. For owners running higher torque, larger turbos, or planning track sessions where the clutch sees sustained hard use, the ACT kit’s organic sprung disc eventually reaches its limit. The Competition Clutch Stage 2 Steelback Brass Plus Kit is the step up for Subaru WRX and Subaru STI owners who need more torque capacity without moving into a full ceramic setup.
This post covers what the Competition Clutch Stage 2 kit provides, how it compares to the ACT kit, and who should make the switch.
What the Competition Clutch Stage 2 Kit Provides
The Stage 2 Steelback Brass Plus kit is part of Competition Clutch’s Street Series 2100 lineup, built around a Carbon Kevlar friction material with a steel alloy backing. This combination provides approximately an 80 percent increase in torque capacity over stock, which gives the clutch significant headroom for builds running higher boost and larger turbos than a stock or mildly modified setup.
The kit includes a performance pressure plate, a high torque sprung disc with antiburst steel-backed Carbon Kevlar facings, all applicable bearings, and the appropriate alignment tool. Because the disc remains sprung rather than solid, engagement stays more controllable than a fully rigid race disc, even though the friction material itself is more aggressive than an organic compound. A 500-mile break-in period is recommended after installation, which allows the friction surfaces to seat properly before the clutch sees its full working load.
How This Compares to the ACT HD Street Sprung Kit
The difference between these two kits comes down to friction material and torque capacity, not just fitment range. The ACT HD Street Sprung kit uses an organic friction disc designed primarily for street drivability, holding up well for STI builds in the 300 to 450 horsepower range. The Competition Clutch Stage 2 kit uses a Carbon Kevlar Brass Plus material instead, which handles significantly more torque before slip becomes a concern.
Fitment is also broader. The ACT kit covers the 2002 to 2014 STI only. The Competition Clutch Stage 2 kit covers the 2004 to 2020 Subaru WRX and STI, which opens it up to WRX owners and to 2015 and newer STI builds that the ACT kit simply does not address. For owners on those newer platforms, this kit is not just an upgrade option, it is one of the few Stage 2 options available at all.
Engagement feel differs as well. The Carbon Kevlar Brass Plus material is firmer than the ACT organic disc, which some drivers notice as a slightly less smooth takeoff from a stop. However, because the disc remains sprung, the kit stays usable as a daily driver for most owners, just with a firmer pedal feel and a more aggressive bite than the ACT kit provides.
When You Need More Than the ACT Kit
The clearest signal that the ACT kit has reached its limit is clutch slip under hard acceleration on a build that has moved beyond what the organic disc was designed to handle. Owners running a larger turbo, E85, or a more aggressive tune than the ACT kit’s intended range often find slip showing up first under high-load conditions, even if the clutch felt fine before the upgrade.
Track use accelerates this timeline. Aggressive street use and moderate track use is exactly the use case Competition Clutch designed the Stage 2 kit around, and sustained high-RPM, high-load conditions on track wear an organic disc faster than street driving alone. For owners planning regular track days on a built WRX or STI, starting with the Stage 2 kit rather than upgrading twice is the more practical path.
Power level is the simplest way to frame the decision. Builds staying under roughly 450 horsepower with primarily street use are well served by the ACT kit. Builds pushing beyond that range, running E85, or seeing regular track time benefit from the additional torque capacity and more aggressive friction material the Competition Clutch Stage 2 kit provides. For STI owners mapping out where a clutch upgrade fits in a larger build, the STI performance upgrade guide covers how drivetrain components like the clutch align with engine and turbo upgrades. The STI engine build and power goals hub covers how clutch capacity should scale alongside a short block and turbo upgrade.
What to Pair With This Upgrade
Because clutch replacement requires dropping the transmission, it is the right time to address related drivetrain components in the same job. Flywheels are commonly replaced during clutch installation to ensure proper engagement and compatibility with the new disc. If the existing flywheel shows wear or heat spots, replacing it alongside the clutch avoids inconsistent engagement on the new friction material.
As torque capacity increases, the load transmitted through the drivetrain increases as well. Transmission mounts help reduce drivetrain movement under that additional load, which improves shift consistency and reduces wear on surrounding components over time. Shifter bushings are a smaller but worthwhile addition, improving shift feel and precision, particularly noticeable when paired with a firmer clutch engagement.
For a broader view of clutch options across both platforms and power levels, the best clutch upgrades for WRX and STI post covers how this kit fits alongside other options. WRX owners building toward higher power can find the equivalent build sequence context at the WRX engine build and power goals hub.
Shop the Competition Clutch Stage 2 Kit
The Competition Clutch Stage 2 Steelback Brass Plus Kit is in stock and ships in 24 to 48 hours. Priced at $675.00.
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