Spec 04-09 STi Stage 3 Clutch Kit

The SPEC SU303 is a Stage 3 single-disc clutch kit for the Subaru WRX STi with the six-speed manual, listed here for the 2004-2009 cars. STi owners shop for it when the factory clutch starts letting go after a tune, bigger turbo or E85 conversion, when launches at the strip or autocross have cooked the original disc, or when the stock clutch is simply worn and the next one needs to survive a lot more torque than the EJ257 made from the factory.

What the clutch kit does in a six-speed STi

The STi drives all four wheels through one dry clutch between the EJ257 and the six-speed gearbox. The pressure plate clamps the disc to the flywheel; the release bearing unloads that clamp when you press the pedal. On a modified STi, the clutch is usually the first part to run out of holding power, because a tune can add a large amount of torque in the midrange where the stock disc has the least margin.

SPEC's Stage 3 disc uses a carbon semi-metallic material in a 6-puck layout, which SPEC describes as an aggressive but streetable engagement for street and race cars. SPEC rates the SU303 at 549 ft-lb of torque and lists the kit at 18 lb. That puts it in the range of heavily modified STi builds. The trade-off for that grip is engagement character: a puck disc grabs quicker than a full-face organic disc, so expect a shorter slip window on takeoff and possibly some chatter when cold.

Symptoms that point to the clutch

• Tach flares in third through fifth at peak boost while speed stays flat
• Slip that gets worse after a few hard pulls as the disc heats up
• Judder or shudder pulling away, especially reversing up a driveway
• A pedal that engages much higher than it used to
• Hard engagement of gears or grinding with the pedal on the floor, which can also be a hydraulic or release problem
• Bearing noise that changes or goes away when the pedal moves

How to confirm before you buy

Log a pull before you blame the clutch. If engine RPM rises faster than the speed trace in a single gear, the disc is slipping; a boost leak or a tune problem will show up as low load instead. Check the clutch fluid level and look for a wet slave cylinder, since a hydraulic fault that keeps the disc partly released will feel like slip or drag. Our slipping diagnosis guide covers the road test and the flare vs. slip guide explains what each feels like. Our clutch chatter page covers takeoff judder.

Fitment

This listing is for the 2004-2009 Subaru WRX STi with the six-speed manual. SPEC's own fitment list for SU303 is broader: it covers the WRX STi six-speed across a wide year range, the 2007-2008 Legacy 2.5L Spec B, and GM LS engine swaps into the STi six-speed that use custom components. It does not fit the regular WRX with the five-speed gearbox, which uses a different clutch. Subaru made running changes over those years, so match your car to the listing and, if anything is unclear, send us your year and VIN and we will confirm before it ships. More options are on our rebuild kits page.

Install notes

• Machine or replace the flywheel. A Stage 3 puck disc on a glazed face is a recipe for chatter. If you want less rotating mass, the Competition Clutch 15 lb STi steel flywheel and the ACT Streetlite flywheel are listed for these cars. See lightweight vs. stock flywheel before you choose.
• Replace the pilot bearing while the gearbox is out, and check the release fork and pivot for wear.
• Use an alignment tool to center the disc, then torque the pressure plate bolts gradually in a star pattern to the factory value.
• Clean all oil and grease from the flywheel and pressure plate faces with brake cleaner before assembly.
• Bleed the hydraulics with fresh brake fluid and confirm the engagement height before driving.
• Bed the disc in with several hundred miles of normal driving before any launches or full-boost pulls.

Does the SU303 fit a regular WRX?

No. SPEC lists it for the WRX STi with the six-speed gearbox and the 2007-2008 Legacy Spec B. The five-speed WRX uses a different clutch.

How much torque is it rated for?

SPEC rates the SU303 at 549 ft-lb, which suits heavily tuned STi builds.

Will a Stage 3 clutch chatter on the street?

It can. The 6-puck carbon semi-metallic disc grabs quicker than an organic disc. A fresh flywheel surface and a proper break-in keep chatter to a minimum.

Do I need a new flywheel with it?

At minimum the flywheel must be resurfaced. Many owners fit a lighter steel flywheel at the same time; we stock STi flywheels from Competition Clutch, ACT and Exedy.

How long is the break-in?

Plan on a few hundred miles of normal driving with no launches or extended slipping before using full power.

• Transmission Slipping Diagnosis Guide
• Shift Flare vs. Slip: How to Tell the Difference
• Automatic vs. Manual Transmission Repair Cost