This is the Stage 2+ (part number SA003H) Spec Clutch with the optional aluminum flywheel (part number SA74A), as it looks right out of the box. The MSRP on the clutch is $539.00 while the aluminum flywheel tacks on an additional $419.00 to this price. If my rudimentary math skills are correct (and they aren’t – I totally used a calculator here) that comes to $958.00. Just for grins I asked the friendly fellow working the parts counter at my local Honda dealer for a quote on a clutch and flywheel and it came to $958. Keep in mind that, in most cases, you can resurface the factory flywheel, reducing your costs with an OE replacement. However, the Honda parts quote did not include a release bearing, something that is recommended with every clutch replacement and is included with the Spec clutch. Spec uses an OE replacement bearing for this application as they’ve found that the factory bearings hold up really well.
I spoke with Shelly Norton from Spec who explained how the Stage 2+ achieves its huge improvement in clamping force over the OE clutch. “The plate load is significantly increased and the disc material has a higher friction coefficient than organic or Kevlar, despite its streetability,” Shelly explained. “This unit holds 300 ft-lbs of torque versus the strongest new OE unit we have tested at 160 ft-lbs.” In case I want to drag race (or challenge a tractor puller to a duel) Spec even offers a Stage 5 kit for my Si with a 440 ft-lb torque capacity.
The clutch cover and diaphragm (or Belleville) spring of the Spec Stage 2+ maintains the same appearance as the factory unit (albeit in a sexier wrapper). However, the Spec spring is indeed stronger due to a more intensive heat treatment.
Unlike any room in my house, this is where the magic happens. Spec’s Stage 2+ clutch contains a multi-friction disc in a full-faced configuration made up of carbon semi-metallic pucks on one side and Kevlar on the other. According to the Spec website, the Stage 2+ “bridges the gap between Stage 2 and Stage 3, offering drivability and an engagement quality characteristic of the Stage 2, but with a 15-20 percent higher torque capacity. The hub is double sprung with spring cover relieves for flexibility and all of the components are heat-treated for strength and durability.”
This side view shows that there is no Marcel spring in the Spec Stage 2+ clutch. Some manufacturers utilize a Marcel spring as an additional cushion between the clutch face and the disc in order to reduce chatter and increase drivability. On the Spec clutch the Kevlar provides the smoothness instead. The big advantage of this is that the release clearance is less so shifts can be faster and the disc is a little easier on syncros. You can also see that the hub stops and drive pins are much heavier than the stock clutch to reduce the chances of hub failure. The disc hub is much stronger than stock.
Lightweight flywheels can be both a blessing and a curse. The benefits are obvious. By reducing the mass that the engine needs to accelerate you effectively improve performance. The engine will essentially wind up through the powerband much more quickly. The drawback is that these lightened low inertia flywheels create a more immediate clutch engagement, which makes driving in stop-and-go traffic a bit more challenging. Another drawback of an aftermarket flywheel is that it does not have the NVH-reducing characteristics of an OE dual-mass unit. Translation – added transmission noise. We threw both flywheels on the scale and measured 16lbs for the factory unit and 8lbs for the Spec aluminum version (keeping with Spec’s claim of 7.97lbs). Half the weight of the factory version! Spec also offers a steel OE replacement flywheel that weighs 14.4lbs as a “this one feels just right” Goldilocks compromise.