Open differential(which is what tC's come with stock) basically directs power to the wheel with less resistance, AKA, the easy way out, So if u had one wheel in a puddle of oil, and the other on hot smooth pavement, the tire in the oil would receive all of the torque rather than the tire with all of the grip, a Limited Slip Differential works completely opposite, giving power and torque to the wheel that has the most resistance, For example, while making a right turn, the LSD would give more power to the left wheel therefore making a much more powerful and smooth turn, with 20psi of boost, LSD is a must, B the way,
www.scionspeed.com has a 400+hp tC doin 12's, check it out