Our Nismo unit came already broken-in with two of its ten clutch plates disengaged on each axle. This gives it 80-percent of its full locking strength (still tight when compared to our Project Z's diff, which is only at 30 percent). As predicted, it does push the car at turn-in, but adjusts the car's attitude easily with mild throttle inputs mid-turn. Had all ten plates been engaged, the on-power understeer would have been significantly more sever and the data much less like the stock viscous LSD (unfortunately, we forgot to record the vehicle yaw data for this).
Quaife Automatic Torque-Biasing (ATB) LSDQuaife's Torsen- or gear-type differential is usually preferred by most road racers. Without writing a dissertation on how the gears transfer torque, we'll just talk about how the unit performs. Unlike the clutch-type or viscous LSD, the Quaife isn't susceptible to wear on the clutch plates or degradation of the dilatant fluid used in viscous diffs. It should also provide the smoothest transfer of torque to the outside wheel and thus the least amount of understeer. Around the figure-eight, the Quaife-equipped car was by far the lightest on its feet, being easily rotatable, with quick smooth transitions from understeer to oversteer. The automatic torque biasing mechanically distributes power to the outside wheel, effectively making it feel similar to Mitsubishi's Active Yaw Control (AYC) system, which throws torque to the outside wheel to help rotate the car under throttle. Understandably, many racers prefer this type.
Stock Nissan Viscous LSDTo see how these aftermarket LSDs compare to factory offerings, we also collected data on the OE-style viscous diff. A viscous LSD uses the fluid viscosity of a dilatant fluid inside a sealed housing to control output shaft speeds. When the fluid is exposed to shearing forces caused by the two axles spinning at different speeds, it thickens up, forcing both output shafts or axles to partially lock and spin at the same speed. Viscous diffs are the most civil and the softest of the three types tested, since they act more like a torque converter instead of using solid mechanical connections to create lock. In theory, it requires the least amount of maintenance, but when exposed to hard-driving conditions, the dilatant fluid has a tendency to break down and degrade from excessive heat, losing its slip-limiting capabilities. Because of its non-mechanical nature, it's also less effective in transferring power.
Manufacturers choose the viscous diff for good reason. It's the most forgiving of the bunch, allowing time for reactions between over- and understeer. It also takes out the understeer/oversteer balancing act required to get around the figure-eight, making it a good choice for the street or weekend track driver with non-aggressive suspension and tires.
Open DifferentialAs a control, we also installed a pumpkin equipped with an open differential. Although not much slower in a competent driver's hands, the open diff requires huge on/off throttle inputs to keep the car in check. After turn-in, the car would continue to understeer massively through the turn. The only way to tuck in the front end is to lift off the throttle and wait for the weight to transfer to the front tires. This results in lurching between oversteer and understeer without ever achieving a decent neutral set.
One scenario we weren't able to test was how each diff reacted when one drive wheel was completely unloaded, such as when the inside wheel catches air if you round a rumble strip too aggressively. We've heard some types will function like an open diff under these conditions.
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