Similar to the gear box shift scenario, the factory gear ratios are a compromise between acceleration and engine/road speed.

An APC diff change provides for LSD combinations right up to 4/11 gears. The change is simple and completed in less than 2 hours for a current Holden and around 6 hours for a BA/BF Ford.

The perception is that the change of the gears will result in high engine speeds at normal cruising speed. The reality is that going from a factory 3.46 to a 3.9 set up will result in around 200rpm higher engine speed at 110km/hr. The higher ratio though provides vastly improved torque delivery and resultant acceleration.