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The flywheel has machined in starter ring teeth that cannot come loose with heat and differing rates of expansion between the ring gear and the flywheel body. A cool thing about the Exedy flywheel is that it can be resurfaced during clutch changes by any local machine shop with nothing special, just like a stock flywheel.
Finally, the Exedy flywheel is spun tested from 15,000 to 18,000 rpm and meet or exceeds SFI standard. It also has a 90 day warranty.
The material is cellulose with copper wire and kevlar fiber woven through it in a resin base. The kevlar improves the material’s burst strength and the copper wire improves both burst strength and helps improve heat resistance. The cellulose promotes smoothness in engagement.
As you can see in this side profile view of the disc, it has a marcel spring. The marcel is a flat wavy spring that goes in between the disc and the friction material. This acts like a cushion to make the engagement smooth with less shock.
The cover of the pressure plate is thicker, which helps increase the clamping force on the disc because it will not deflect as much. The WRX pressure plate is a pull type.
The pull type pressure plate is advantageous because the pressure plate is a lot more efficient since the pressure plate is loaded in one direction only (toward the transmission), and the diaphragm is supported closer to the clutch bolt flange. There is therefore significantly less deflection in the cover which is basically wasted pedal travel.
Check out the drive straps which transmit the engine’s torque to the input shaft when the clutch is engaged. Stock clutches have one strap, and most heavy duty/race type clutches have two straps stacked upon each other. The Exedy stage one has three!
