OS Giken utilized its accumulated racing knowledge and engineering experience to develop its own limited slip differential. Four years of extensive research and development lead to a new and revolutionary LSD design with the capacity to house an unprecedented number of friction plates and thus the OS Super Lock LSD was born.

Over the last few weeks, I’ve been driving my 08 Subaru STI equipped with the new front and rear prototype OS Giken LSD (limited slip differential) for street and track testing. We’re starting off with a 1-way in the front and a 1.5-way in the rear, although that may change depending on what kind of performance we start to see on track. When OS Giken decided what configuration we would use, they had in mind to attain the best balance for a daily driver that also happens to see regular track time.

I can safely say that while I’ve had the pleasure of driving several Subarus which have made use a number of different LSDs and manufacturers, OS Giken sets the bar at a level which no other I’ve experienced has yet to achieve. The OS Giken LSD is a clutch type and operates by distributing torque bias based on which of the two output shafts is under more load, as opposed to locking the two output shafts to spin at the same speed. However unlike a Torsen torque biased differential, the OS Giken distributes the torque evenly and the amount of lock will vary with the force being applied to the unit.

The key is progressive locking despite varying inputs, allowing the OS Giken LSD to perform smoothly and predictably. A lot of other LSDs will make violent noises during turn-in or actually hop quite severely at low speeds as a result of the LSD design. Normally clutch LSDs can’t fully lock and to compensate, require an increase in pre-load by adding shims. Essentially what’s happening is that the initial locking range of the LSD might be somewhere around 10-60% and by bumping up the initial torque they’re increasing the locking capability range an additional 10% while sacrificing low speed drivability.

Now the reason why OS Giken’s LSD is able to fully lock despite being a clutch type is due to the amount of plates it’s able to house (up to double its competitors). You’ll also find that the disks have more usable surface area, offering a significant advantage in the field. More importantly, installation is not extraordinarily complex and does not inspire any check engine lights to come on. Currently we’re using Motul Gear 300 75w90 in the transmission and a liter of Gear Competition 75w140 in the rear differential casing. Using high end fluid is critical as the LSD is expected to endure high temperatures and for dedicated performance, OS Giken recommends the use of their own OS-250R fluid.

Naturally I’ve been so far nothing but short of amazed at the performance the car is now exhibiting. I won’t be testing the LSD’s performance on track until this coming weekend at Redline Time Attack, nonetheless I do have reasonably high expectations justified by the high speed and tighter local street corners I’ve been able to sample in my daily commute already. I’m confident that with OS Giken’s help, I’ll be able to express a saying I’ve recently become fond of, “Enter like a man and come out like a beast.” As I’m able to log more testing, I’ll be able to enhance this review with supplemental feedback.