ACT 2004 Subaru Impreza XACT Flywheel Prolite
The ACT 600240 is the lightest flywheel ACT makes for the Subaru WRX STI with the EJ257 turbo engine and six-speed gearbox. It fits the 2004 Impreza WRX STI named in the listing and carries forward through the 2021 STI, plus the 2007 to 2009 Legacy GT spec.B. Buyers usually land here for one of two reasons: the factory flywheel is scored, hot-spotted or worn past resurfacing during a clutch job, or they want the engine to rev and fall faster on a rally, autocross or road course car. At 11.8 lb it is built for the second job first.
The flywheel bolts to the crank, carries the 124-tooth starter ring gear, and gives the clutch disc its rear friction face. On the STI it also sets how much rotating mass the EJ257 has to spin up between shifts. ACT machines the 600240 from one piece of heat-treated chromoly steel with a 240 mm friction surface and an induction-hardened ring gear, and it is rated to SFI 1.1. Pulling weight off this part sharpens throttle response and rev-matching, but ACT is plain that the Prolite trades away some drivability: expect mild to moderate gear rattle at idle and a car that needs a little more throttle to pull away cleanly. If the car is mostly a daily driver, the heavier ACT Streetlite 600235 is the more comfortable choice.
Most flywheel problems feel like clutch problems, so rule out hydraulics and the disc first. Our slipping diagnosis guide covers the road tests that separate a worn disc from other causes, and the clutch chatter guide walks through engine mounts and contamination. Once the transmission is out, inspect the old flywheel face for heat checking, measure runout, and decide with our resurface vs replace guide. If you are on the fence about going this light, read lightweight vs stock flywheel first.
ACT lists the 600240 for the 2004 through 2021 Subaru WRX STI 2.5L turbo (Impreza WRX STI through 2014 and the standalone WRX STI from 2015) and the 2007 to 2009 Legacy GT spec.B 2.5L. It is a six-speed STI part only; it does not fit the five-speed WRX, the 2.0L FA20 WRX, or automatic cars. If your car has a swapped engine or gearbox, send us the year and VIN and we will confirm before it ships. More parts for these cars are in our hard parts section.
| Brand | ACT |
| Part number | 600240 |
| Fits | ACT 2004 Subaru Impreza XACT Flywheel Prolite |
| Vehicle fitment | Subaru Impreza Xact (2004) |
| Type | Flywheels |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Yes. ACT lists it for every WRX STI from 2004 through 2021 with the 2.5L turbo and six-speed, and for the 2007-2009 Legacy GT spec.B. It does not fit the 2.0L WRX or any five-speed car.
The 600240 weighs 11.8 lb. It is ACT's lowest-inertia option, so the engine revs up and drops faster between shifts. The tradeoff is some gear rattle at idle and a touchier launch, which is why ACT recommends Prolite for road race and rally use.
ACT ships the 600240 with a PB1004 pilot bearing, so you have one in the box. Replace it whenever the flywheel is off.
Yes. ACT flywheels are serviceable and can be resurfaced without buying extra parts. Keep the step height correct when it is machined so the clutch clamp load stays right.
No, but the clutch must match the flywheel step. ACT designs its flywheels around its own kits; if you run another brand, confirm that kit is meant for a stock-step flywheel.
