yesterday i called phantom grip and talked to a tech that does the actual installs. they have 3 different sets of tuning springs. the extreme springs make it very tight and the unit is set up to have a .005-.010" space between the unit and the side spider gears BEFORE the unit retention clips are removed from the it. when you get it, it is loaded and has retention clips that hold the unit together so that it can be installed. once the clips are removed, the unit loads itself against the side spider gears with the springs inside. the preload rating is of the spring pressure that you use. he also told me that the unit material is heat treated and conditioned to be used with the spider gear material. this conditioning gives it the funtion of clutch material but doesnt wear out like a loose clutch pack does.
after talking to him, i am going to go with the phantom grip unit with the extreme spring setup. i have 2 graphs from phantom rip. they are of straight acceleration and a with and without the unit installed. the graphs show wheel speed VS car speed.
this one is without the unit installed
this one is with the unit installed
the tech also told me that from his on hand experiences of installing these units, the average reduction in 60' times are 3/10-6/10 of a sec over an open diff