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Spec Stage 2 clutch kit with aluminium flywheel

Lightweight aluminium flywheel with steel insert

Worn slave cylinder

At 110k miles (178 000 km), the car had developed the "clutch pedal stuck to floor"  issue when shifting at high RPMs. This is caused by a worn slave cylinder, where worn seals allows dust to enter the circuit and cause the slave cylinder to get stuck by the high inertial forces and the increased friction. A sure sign of this happening is that the clutch fluid gets discolored again quickly after a change.

State of stock clutch

The car still had the stock clutch, which was in a surprisingly good state for the milage. Minimal surface wear and only a few small hotspots, one could even mistake the clutch disk for a new item.  So the OEM clutch from LUK is more than capable of handling the LS6 stock power. 

However, with everything else disassembled, it would be dumb not to replace the clutch now, as it will probably not last another 20 years.

Spec Stage 2 clutch kit

I had originally purchased a LUK OEM clutch kit from Summit Racing which, unfortunately, was damaged on its way to Norway (link). It took infinite time to try and get that resolved, and in the end I simply had to purchase yet another clutch kit. I was lucky to source a lightly used Spec stage 2 clutch kit from a nice fellow in Alabama, who sent the parts to Norway in a box as secure as Fort Knox. This kit included a lightweight aluminum flywheel. The total weight saving is 4.8 Kg (10.6 lbs).

Less rotating mass is free power to the wheels, as there is less mass to accelerate for the engine. For reference, try to spin the wheel on your bicycle vs a car wheel, you can bring the lighter bicycle wheel up to speed with less force and in less time than the heavy car wheel - the engine will feel the same.

The Spec clutch has a higher clamping force and torque rating than the LUK clutch, but it does not have the self adjusting pressure plate (SAIC). This mechanism is prone to failing, and could possibly be a factor in the "clutch pedal stuck to floor" issue, so I'm ok without it.

Installing the new clutch kit

Prior to installing the new clutch kit, I made sure to fix all oil leaks at the rear of the engine
New flywheel installed. With ARP flywheel bolts and very tight tolerances, I had to carefully clean the bolt holes in the flywheel and every mating surfaces using a Scotch-Brite pad. The flywheel bolts are torqued to 102 Nm (75 ft lbs) and secured with red Loctite.

Clutch balancing

If you noticed the holes drilled in the flywheel and clutch cover, this is the work of Cylmo AS as they balanced the parts. The flywheel and clutch cover had a total imbalance of 120g (4.2 ounce)! For reference, a wheel with an imbalance of only 20g (0.7 ounce) is quite noticeable. Imagine a clutch spinning at 6000 rpm with an imbalance of 6 times that!

After balancing the imbalance was reduced to a total of only 4 g  (0.14 ounce)

New pressure place and clutch disk in place. I'm using the propeller shaft to center the clutch disk, as this obviously has tighter tolerances than the plastic fantastic tool that is included with the clutch kit.

At this stage, I've only tightened the bolts enough to seat the pressure plate, I'll apply Loctite and tighten the bolts to final torque after having mounted the torque tube. This leaves the option to release the clutch disk if one can't get the pilot bearing/clutch disk/propeller shaft to line up when mounting the torque tube.