Porsche has offered the ZF clutch-pack type limited slip differential in almost all 911's and 930's since 1966. These units are quite strong and can be set for locking factors of 40% to 80%. The clutches need replacement under racing conditions to maintain proper lockup but these are quite trouble free. An 80% locking factor is difficult to drive on the street, especially in wet conditions, but for open track racing these are quite popular. Street or Autocross usage requires the LSD to be set at 40%; simple to do with the proper parts.
There are now other LSD options for 901, 915 and G50 transmissions called Torque-Sensing differentials. These are gear-type units as opposed to the ZF clutch-type ones, and do not require any parts to maintain optimum performance. This unique, patented design allows full differentiation between the wheels as well as providing power to both sides and they produce less understeer than the Factory LSDs. Guard Transmission makes an excellent one as well as the unit from Quaife.
For Autocross and normal street driving ,the Torque-Sensing units are more benign in their operation but they do not improve the handing like the Factory clutch-pack units do. The ZF or Guard Transmission LSD's(clutch-type) really stabilize the car under braking and help reduce trailing throttle oversteer.
(Guard har både en "gear-type" TBD och en "clutch-type" LSD)
http://www.guardtransmission.com/app_930.html
