Competition Clutch 04-20 Subaru STi Stage 4 - 6 Pad Ceramic Clutch Kit

The Competition Clutch 15030-1620 is the Stage 4 six-pad ceramic clutch kit for the Subaru Impreza WRX STI and WRX STI with the 2.5L turbo EJ engine and six-speed gearbox. It is meant for STI builds that make well beyond stock power: big-turbo cars, E85 builds and drag or rallycross cars that launch hard and slip any organic or segmented disc. If your STI is lightly modified and driven daily, read the street-use notes below before choosing this step.

What the Stage 4 kit does in an STI

Every 2004-2021 STI six-speed uses a pull-style clutch, with the release bearing locked into the diaphragm and pulled rearward to free the disc. Competition Clutch builds the 15030-1620 for that pull-style car. The Stage 4 Strip Series pairs a performance pressure plate with a sprung disc carrying six ceramic pads instead of a full ring of friction. The maker rates it at up to 250 percent more torque capacity than stock, and says the pressure plate and disc grow from 230 mm to 250 mm. Concentrating clamp load on six ceramic buttons gives huge holding power and heat tolerance, at the cost of a sharp, almost switch-like engagement. The kit includes the pressure plate, six-pad disc, throwout bearing, pilot bushing and alignment tool.

Symptoms that point to a Stage 4

• A Stage 3 or other upgraded clutch that slips again after a turbo or fuel upgrade
• RPM flare on hard launches or at the top of third and fourth at full boost
• Repeated glazing or burnt smell after drag strip or rallycross events
• Judder on takeoff from a disc that has been overheated
• Release bearing noise that comes and goes with pedal travel

How to confirm before you buy

Start with a logged pull in fourth gear and compare RPM to vehicle speed. If engine speed climbs without matching acceleration, the clutch is slipping. If the car simply feels down on power with no RPM flare, look at boost control, knock correction and the tune instead. Check the clutch hydraulics as well: a weak slave cylinder or air in the line causes drag and grinding that a new clutch will not cure. Our slipping diagnosis guide covers reading those symptoms. Then match the clutch to the car. The Stage 3 15030-2600 segmented ceramic kit is rated up to 150 percent over stock and is the friendlier choice for a street STI; the Stage 4 is for cars that need the extra margin.

Fitment

Competition Clutch lists the 15030-1620 for the 2004-2014 Subaru Impreza WRX STI and 2015-2021 WRX STI 2.5L turbo with the pull-style clutch. Our listing is titled 2004-2020. It does not fit the five-speed WRX or the 2.0L and FA-engine WRX models, which use different clutches. The maker's description mentions a billet flywheel where applicable, but the specification table for this part number says the flywheel is not included, so treat this as a clutch-only kit. If your car has a swapped gearbox or you are unsure of its history, send us your year and VIN before ordering. More STI clutch parts are in the rebuild kits category.

Install notes

• Fit a new or resurfaced flywheel and a new pilot bearing or bushing, as Competition Clutch's install sheet requires. The 2-721-ST 15 lb steel flywheel is listed for the 2004-2011 STI.
• Remove the old pilot bushing from the crank before fitting the new one; a slide-hammer puller makes this easy with the engine in the car.
• Clean the rust-preventive film from the flywheel and pressure plate friction faces with a residue-free cleaner.
• Use only a trace of grease on the input shaft splines; the maker warns that too much grease can damage the disc and void the warranty.
• Center the disc with the alignment tool, tighten the cover bolts by hand in a crisscross pattern and keep the gearbox supported so it never hangs on the input shaft.
• Bleed the clutch with fresh brake fluid of the grade on the reservoir cap, and shift often during the first 500 miles of break-in.

When the pads wear down, the 99707-1620 six-puck replacement disc renews the friction side without buying a complete kit.

Does the 15030-1620 fit a regular WRX?

No. It is listed for the six-speed, pull-style WRX STI 2.5L turbo: 2004-2014 Impreza WRX STI and 2015-2021 WRX STI. Five-speed WRX models use a different clutch.

Stage 3 or Stage 4 for my STI?

Competition Clutch rates the Stage 3 15030-2600 at up to 150 percent over stock and the Stage 4 15030-1620 at up to 250 percent. Choose Stage 4 only if the car makes big power or launches hard; for a street-driven STI, Stage 3 engages far more smoothly.

Is a flywheel included?

Plan on no. The maker's specification table lists the flywheel as not included. Use a resurfaced flywheel or a new one such as the 2-721-ST steel flywheel.

Will a six-pad clutch chatter?

Six-pad ceramic discs engage abruptly and can chatter at low speed, especially in stop-and-go traffic or while backing up a hill. That is normal for this type of disc and is why it is sold as a strip series clutch.

Can I replace just the disc later?

Yes. Competition Clutch offers the 99707-1620 six-puck sprung replacement disc, which we also stock.

Is there a break-in?

Yes. The maker says to shift as often as possible during the first 500 miles so the disc beds into the flywheel and pressure plate before hard use.

• How to Diagnose Transmission Slipping
• Shift Flare vs. Slip: How to Tell Them Apart
• Automatic vs. Manual Transmission Repair Cost