ACT XACT Prolite Chromoly Flywheel - 2004-2021 Subaru WRX STI (600240)

Maximum Acceleration & Ultra-Low Inertia for Track Builds
If you are building a dedicated track car, a high-RPM time attack weapon, or a drag car that needs to snap through gears as fast as physically possible, the ACT XACT Prolite Flywheel (600240) is the ultimate solution. Dropping down to a featherweight 11.8 lbs (compared to the 15.6 lbs Streetlite and the heavily bloated stock dual-mass units), this is the lightest safe single-piece steel flywheel on the market for the EJ platform. By shedding maximum rotational inertia, it unleashes instantaneous throttle response, lightning-quick rev-matching, and lightning-fast acceleration.

Monolithic Forged Strength (No Multi-Piece Weak Links)
Many ultra-lightweight flywheels are made from aluminum with bolt-on steel friction plates. Over time, extreme track heat cycles can cause those multi-piece setups to warp, loose tolerances, or throw starter ring gears. ACT completely eliminates this point of failure. The XACT Prolite is CNC-machined from a single piece of hot-forged 8740 chrome-moly steel. It provides uniform heat transfer away from your clutch disc to eliminate heat spots, boasts a rigid structure that is three times stiffer than aluminum, and holds a strict SFI 1.1 safety registration.

• Lightning-Fast Engine Response: Drastically drops rotational mass, letting the engine rev up and down with motorcycle-like urgency.
• Mono-Block Chromoly Durability: One-piece forged layout removes the risk of loose ring gears or separate warped friction inserts under hard track use.
• Precision CNC Machining: Computes an exact, uniform balance profile for vibration-free operations at extreme high-RPM limits.
• Induction-Hardened Ring Gear: The integral 124-tooth ring gear features lead-in chamfers for reliable starter motor engagement and longevity.
• SFI 1.1 Certified: Officially track-approved and structurally tested to meet competitive motorsport safety rules.

Technical Specifications:

• Part Number: 600240
• Flywheel Series: XACT Prolite
• Material: Hot-Forged Chromoly Steel
• Product Weight: 11.8 lbs
• Friction Surface Diameter: 240mm (9.4 in.)
• Ring Gear Tooth Count: 124-Tooth
• Engine Balance: Internal
• Safety Certification: SFI Specification: 1.1 Registered
• Recommended Use: Race / High-Performance Track Applications

Fitment:

• Subaru WRX STI / Impreza 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)
• Subaru Impreza WRX STI [JDM Models Only]: 2002, 2003, 2004, 2005 (2.0L Turbo 6-Speed Manual)

The Nameless "Installation" Pro-Tip:

Street Drivability Warning (The Real Talk): Because the Prolite model drops down to an ultra-low 11.8 lbs, it lacks the rotational inertia required to damp out normal engine variations at low speeds.

What to expect on the street:

1. Increased NVH: You will experience noticeable gear rattle / transmission chatter when idling or decelerating in lower gears.
2. Ghost Misfire Codes: Due to how quickly the crankshaft can fluctuate in speed with such low mass, hyper-sensitive factory ECU sensors can occasionally misinterpret this acceleration fluidity as an engine misfire, throwing a false Check Engine Light (CEL).

If your car is a dedicated street daily driver, do yourself a favor and stick to the ACT Streetlite (600235). If your car lives at the track or you don't mind a raw mechanical experience (and have a tuner who can adjust crankshaft speed sensor sensitivity thresholds), the Prolite is the ultimate performance unlock.

Installation Note: Always replace your flywheel bolts when installing a new unit. We highly recommend picking up a fresh set of high-tensile ARP Flywheel Bolt Kit (260-2801) to ensure proper torque retention and safety against the crank.