I found this info on this page http://www.intellexual.net/faq.html
It says some open diff's may seem like a LSD or it's a 1-way
Differentials are gearboxes that transmit power from the driveshaft to the rear axles in a way that allows each wheel to spin independently of the other. The SC coupes came with open differentials, which do not transfer torque between wheels when one is losing traction (slipping). In fact, under most circumstances, the open diff. only gives one wheel all the power. Thus the need for limited-slip differentials (aka: Positrac). Limited-slip differentials (LSD) transfer power to the wheel with the most traction, which allows you to deliver more power to the ground. There is a wide array of LSD options out there. The trouble is in matching the overall drivetrain ratios. If your final drive ratio is off, your speedometer and odometer will also be off. The most popular LSDs used are the Torsen Supra and Supra TRD LSDs because they are direct bolt-ons. Be aware that there are many versions of the Supra differential, including some that are actually open differentials!
LSDs are categorized as 1.0 limited-slip, 1.5 limited-slip, and 2.0 limited-slip. Here are the distinctions:
Open differential - will power only one wheel at almost all times. Some open differentials will give the appearance of being limited slip when (1) power brake launching, (2) when good traction is avalable, and (3) when the car is pointed forward and not turning.
1-way Limited-slip - provides power to both wheels when the car is traveling straight and no other time. The weakest linking differential of all LSDs.
1.5-way Limited-slip - provides power to both wheels when the car is traveling straight and turning. Moderate grip while engaged.
2-way Limited-slip - provides power to both wheels when the car is traveling straight, while turning, and while braking. Fully engaged limited-slip at all times.
- (info provided by VSsc400)
Anthony