ACT ProLite Flywheel – 2004-2021 Subaru STI

ACT ProLite Flywheel for the 2004-2021 Subaru WRX STI

The ACT ProLite Flywheel for 2004-2021 Subaru WRX STI is a lightened steel flywheel replacement that reduces rotational mass compared to the heavy OEM unit. Lighter flywheel mass improves throttle response, makes rev-matching easier, and allows the engine to accelerate through the RPM range more quickly. A direct bolt-on replacement using the factory mounting points.

DETAILS

• Flywheel type: ACT ProLite
• Material: machined steel
• Reduced mass vs OEM flywheel
• Maintains correct balance and SAE specification
• Direct bolt-on replacement
• Fitment: 2004-2021 WRX STI

ACT flywheels are machined to application-specific tolerances rather than adapted from a generic blank. The correct bolt pattern, SAE spec, and balance specification for the application are maintained. Flywheel surface finish is machined to the specification required by the clutch disc friction material for correct break-in and long-term performance.

Installing the flywheel at the same time as a clutch replacement adds minimal additional labor, the transmission is already removed. ACT’s flywheel and clutch kits are validated together, but the standalone flywheel is also compatible with OEM clutch systems for owners who are replacing only the flywheel.

What’s in the Box

• ACT flywheel
• Flywheel bolts
• Installation instructions

Why Choose ACT

Advanced Clutch Technology has been manufacturing performance clutch systems in the United States since 1993. Every ACT pressure plate uses a proprietary diaphragm design that increases clamp load and reduces deflection compared to OEM units, and every diaphragm goes through a four-stage heat-treating process before it leaves the factory. The result is a clutch system that holds more power than the stock unit, engages more precisely, and lasts longer under the kind of driving that wears factory clutches out quickly. ACT designs each application from scratch rather than modifying OEM tooling, which means the fitment is precise and the performance is intentional. Whether the build is a street-driven daily driver or a dedicated track car, ACT offers a kit at the correct specification for the use.

The RallySport Take

The ACT ProLite flywheel for the 2004-2021 WRX STI is a direct upgrade to the heavy OEM flywheel. Reduced rotating mass is one of the highest-return modifications on naturally aspirated engines, and on turbocharged platforms it improves the throttle response feel significantly. Install at the same time as a clutch replacement, if the flywheel is already out, upgrading it adds minimal labor cost. Fits the models listed in the fitment table below.

Fitment