Clutch Masters 850 Series Street Twin Disk Clutch Kit for 2004 – 2021 WRX STI
Even with basic bolt on mods the EJ25 motor in your STI will be getting close to 300HP or even more with some of the newer models of STI’s. At this power level the stock clutch becomes incapable of supporting the upgrades and more aggressive driving from track days. The 850 twin disk clutch offers a significant increase in holding capacity over factory clutch and is a must have to put the power to the ground for any track ready WRX STI, while also shaving rotating mass from your engine!
This 850 series kit is a 8.50″ (216mm) twin disc clutch with a custom cover plate that is machined from billet aluminum and is then Type 3 hard anodized. By machining the strongest cover possible while maintaining minimal weight, Clutch Masters was basically able to eliminate any flex in the cover. The billet covers see only .003″ of flex where as a cast or stamped unit can see as much as .030″ of flex. By eliminating this flex in the cover, the driver is able to operate the clutch much more consistently and confidently. The strength of the covers also results in greater clamping force over the same amount of area vs a cast or stamped cover. This means the twin discs are easy to drive and have superior clamping force to make sure all the power your engine is making is being utilized.
What makes the 850 kits truly special, and a feature unique to Clutch Masters is the QR System, or Quick Release Pressure Plate. The QR System Incorporates three spring-loaded bolts allowing the pressure plate to engage and disengage evenly and smoothly while reducing internal clutch noise/chatter by up to 50%. The QR System was developed to provide quiet and smooth operation for the user while delivering the performance a race clutch needs.
While being very similar to the 725 Series 15017-TD7S-SHV having the one organic and one ceramic disc for a smoother engagement, the main differences are the estimated power holding capacity and not having the push type conversion. The 725 series clutch kit mentioned above is rated for around 850 horsepower, the 850 series clutch kit is rated for 1100 hp for your extreme power goals and ensuring the power goes to the ground due to the larger friction surfaces.
- Hard Anodized Aluminum Cover Assembly with attached Diaphragm
- Titanium reinforcement bushings for the Quick Release Pressure Plate system.
- Pressure Plate Ring
- Quick Release Pressure Plate System
- One Ceramic Disc
- One Organic Disc
- One Floating Mid Plate
- Lightweight Steel Flywheel
- Release Bearing
- Pilot Bearing
- Pressure Plate Bolts
Flywheels are made for each specific application in steel and meet SFI spec 1.2 for competition in NHRA, NDRA, IDRC, IHRA, SCCA and NASA.
This kit is specifically designed for the serious drag racing with very significant modifications to their WRX STI, and most importantly one of our infamous Brewed tunes.
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