The Blackline helical LSD is the preferred option on a street car because of its low maintenance and smooth operation, the configuration is similar to the parallel axis Torsen unit used in Audi Quattro. The Mazda MX5/Miata differential is used in many kit cars due to the low cost and suitability as a donor.
There is a detailed comparison on www.miata.net which compares the characteristics of a Miata viscous LSD, the Torsen helical LSD and the Tochigi Fuji Super 'Cone Clutch' LSD - we can supply a copy on request.
Note: This unit can also be used on 1.6 MK1 models but needs the 1.8 diff housing, prop and drive shafts.
Helical LSD Advantages:-
Equal rotational speed to both wheels
Torque distributed according to traction
Minimal service requirements - no clutches
Quick reaction compared to viscous LSDs
Gentle and progressive engagement, low noise
Easily controlled power take-off and drifting
Gears and body manufactured from 8620 alloy steel
Direct replacement into stock differential
Blackline Helical LSD's - How They Work
The Blackline helical LSD's are torque biasing, that is they distribute torque between the wheels, loading more torque towards the wheel with the best traction thus improving performance and driveabitily. Especially in low grip situations. The helical gearing manages the distribution of friction within the LSD. When torque is applied to the helical gear system it creates force that pushes the gear into the differential body, thus creating friction. Increases of torque, increases the thrust force directly proportional to the amount of torque. This allows the Blackline LSD to cope with considerable traction imbalance even under heavy power conditions, as would be the case on exiting a powered up corner. But at low torque conditions the LSD can differentiate quietly and smoothly, thus making the differential very suitable for normal road driving. The Blackline LSD uses the popular parallel axis helical geared configuration optimised for even load distribution. They are designed with a torque bias of 5:1 this means that if one wheel loses traction then the wheel with the most grip can receive five times as much torque as the wheel that is slipping. However, five times zero is still zero, so all these helical LSD's work best when both wheels are 'planted' and some traction is still available on the slipping wheel. In practice this is rarely a problem as there is always some 'drag' on the slipping wheel, however some drivers expertly use left foot braking to partially lock the spinning wheel. Note - Helical LSD's work especially well when combined with modern anti-lock braking systems.