We lost ourselves in Project EVO's newfound performance, enjoying its ample 323 lag-free whp quite frequently. Perhaps we were enjoying it a bit too much because our clutch started to slip. Frankly, we were surprised that the stock clutch held up so well against the abuse. We decided live with its pleasant-to-drive manners to the bitter end.
Since we have higher power goals on the way for Project EVO, we needed to get a clutch that would contain big power yet be friendly to drive as practical transportation. Since launching AWD vehicles can punish clutches in a multitude of evil ways, we needed to get something significantly tough. Usually race type clutches with a high torque capacity are unstreetable, on/off grabby light switches. Although able to take torque and heat, race type clutches typically wear quickly when slipped and driven under street conditions.
Race type clutches also tend to hit hard and thus put a lot of stress on the transmission, axles, transfer cases and the rest of the drivetrain. After doing a bit of research we turned to Nukabe Automotive, Cusco's official North American distributor to let us test Cusco's Super Twin, twin-disc clutch. The Cusco Super Twin has the reputation dichotomy for being able to take power and AWD punishment while still being streetable. A twin-disc clutch is just like the name sounds, it has two discs; the advantage is literally you have the torque handling of nearly two clutches in a small, compact package.
Usually twin-disc clutches use two smaller discs. The advantage is that when there are two clutch discs you can get away with smaller diameter discs and pressure plate, which reduces inertia considerably. This gives you quicker revs, faster shifts, easier heel-and-toe downshifting and better acceleration.
A disadvantage to a twin-disc is that since a twin-disc clutch has four wear surfaces, a twin-disc ,if it's slipped a lot as in ordinary driving, experiences accelerated wear and a rapid drop-off in clamp load from the pressure plate with subsequent slipping. This sensitivity to wear can make rebuilding a twin disc in a daily driver an annoyingly frequent occurrence.
We had our doubts as to the Super Twin's streetable and long-term durability as we have used plenty of race-type multi-disc clutches on other cars in the past. Race type dual discs are the king of grabby. They are nearly impossible to modulate with no engagement travel. They are light switches. Dual disc clutches are usually low inertia as well which is great for quick throttle response while racing but when combined with the grabbiness and short engagement, make for a clutch that is only suited for racing and nearly impossible to drive in stop-and-go traffic.
To make matters worse, when the clutch is disengaged, the floaters and plates in the clutch rattle and clank around making a noisy "chingging" sound. It sounds like something is seriously wrong with your tranny and even if you know what the noise is, it's super annoying. Twin-disc clutches usually have solid hub discs as well. Although these are good for low inertia and crisp shifting, they make the engagement even harsher and transmit all sorts of noises through the drivetrain into the car.
With all of this negative multi disc clutch experience, we were skeptical when the guys at Cusco recommended the Super Twin and said no problem when we expressed our past experiences and concerns. The Cusco clutch has many unique and ingenious features that tame the beast giving us the advantages of a twin-disc clutch with few of the disadvantages.