XClutch 15-21 Subaru WRX STi Base 2.5L Stage 1 Extra HD Sprung Organic Clutch Kit
The XClutch XKSU24001-1AX is the Stage 1X kit for the 2015-2021 Subaru WRX STI with the 2.5L turbo and six-speed manual. It is meant for the STI owner who has gone past bolt-ons, with a tune, a bigger intercooler or more boost, and now feels the factory clutch let go in fourth, fifth or sixth, but who still drives the car every day and does not want the grab of a ceramic or puck disc. Stage 1X keeps an organic, sprung disc and puts a much stronger pressure plate behind it.
XClutch builds the 1X around one idea: more clamp load on a street-friendly friction material. The heavy duty cover raises clamping force by 40 percent over the factory unit, and XClutch rates the kit at 510 ft-lb of torque capacity, a figure that includes its safety factor. For comparison, the steel-backed Stage 1 kit for the same car is rated at 420 ft-lb, so the 1X is the step for an STI that has outgrown a basic Stage 1 but is not a drag car.
The disc is 9 7/16 in organic with a sprung hub. Organic friction engages progressively and is easy to slip gently in traffic, and the springs in the hub soak up some of the shock that a hard shift sends through the gearbox and center differential. XClutch lists the kit for street use. Expect a heavier pedal than stock, since a stronger diaphragm spring takes more effort to release, and XClutch notes that any upgrade can change noise and vibration in the cabin.
In the box: pressure plate, disc, release bearing, pilot bearing and an alignment tool. The flywheel is not included. The disc fits the 1 in, 24-spline input shaft, and XClutch lists a flywheel step of -0.590 in.
A slipping clutch does not set a trouble code on its own, so a clean scan does not clear the clutch.
In fourth gear from about 2,500 rpm, go to full throttle and watch the tach against the speedometer. If rpm rises faster than speed, the clutch is slipping. A boost leak makes the car feel flat without that rpm flare, so log boost during the same pull. Check that the pedal has free play, too: XClutch's TSB-161 warns that too little free play at the master cylinder pushrod can cause early slipping. Our slipping diagnosis guide and flare vs. slip guide walk through reading those symptoms.
This kit is listed for the 2015-2021 WRX STI with the 2.5L turbo and six-speed, which uses a pull-type clutch. It is not for the 2.0L WRX, which takes a different kit, and it is not the twin-disc setup. If your car has an aftermarket flywheel, confirm its step matches before ordering. Send us your year and VIN if you are unsure. More STI clutch parts are in the rebuild kits category.
If you want an easier pedal and the car is closer to stock power, the Stage 1 sprung organic kit (1A) is the lighter option. If you mainly want a disc that resists coming apart at high rpm, the Stage 1 steel-backed organic kit is rated at 420 ft-lb.
| Brand | XCLUTCH |
| Part number | XKSU24001-1AX |
| Fits | XClutch 15-21 Subaru WRX STi Base 2.5L Stage 1 Extra HD Sprung Organic Clutch Kit |
| Vehicle fitment | Subaru Wrx Sti (2015-2021) |
| Type | Clutch Kits - Single |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
No. It is listed for the 2015-2021 WRX STI with the 2.5L turbo and six-speed pull-type clutch. The 2.0L WRX uses a different clutch and has its own XClutch kits.
XClutch rates the Stage 1X kit at 510 ft-lb of torque capacity including its factor of safety, with 40 percent more clamping force than the factory pressure plate.
No. The kit includes the pressure plate, sprung organic disc, release bearing, pilot bearing and alignment tool. Resurface your flywheel or buy a new one, such as the XFSU003C chromoly flywheel.
Yes, somewhat. A heavy duty cover with 40 percent more clamp load takes more effort to release. The organic disc still engages smoothly, which is why XClutch lists it for street use.
XClutch's FAQ calls for a bed-in period of about 1,000 km of normal driving, with no launches or full-power shifts, before using the full torque capacity.
Inspect the release fork contact points and pivot, the rear main seal and the slave cylinder. XClutch notes that worn forks, pivots and hydraulics affect clutch feel and life.
