[Gary C]

The Phantom grip LSD uses absolutley nothing more than spring loaded friction plates between the two output shafts. This is not the best setup in my mine, reason being, it's a fixed preload, never locks up, nor disengages and allows for a 'full functional' differentail action like a torque biasing differential, like a quiaffe, or torsion diff would.
THe reason they work for drag is the fixed preload is greater than the typical torque imbalance that will occur when you're spinning the wheels taking off from a stop in a straight line. As long as neither tire has traction, the torque imbalance is low. Such as when your launching from a dead stop and get wheelspin, due to your power overcoming the traction available from the tires on the ground.
Where it (phantom grip_ fails is any unequal traction situation, such as one tire on pavement, the other on wet pavement. The
engine torque multiplied by the gear ratios will overwhelm the preloading of the plates with the spring b/w them which acts on the spider gear in the diff, and thus you will just spin freely with virtually zero power going to the tire with more traction and the tire on ice will spin freely. However.. you will still accelerate, though slowly, as the preload will shunt a bit of torque to the side with more traction, thus making it not completely worthless, just inefficent at what it is supposed to do.
Again, in road racing/auto-x situations where you will want the outside tire *with more weight on it, thus better traction* to get more power than the unweighted inside tire, the phantom grip is virtually worthless as well. The tractino imabalance is high, and your inside tire will still get the majority of power since it has the path of least resistance.

I *personally* prefer a good torque biasing diff, like a quaiffe, or kaaz. Though more expensive, they certainly do a much better job in all situations than the phantom grip does. It's true when it comes to LSD's in that you do get what you pay for. I've driven everything from cars with welded diff's to a phantom grip equiped honda civic (built for SCCA SOLO racing) to driving many a car with quaiffes and the like in them. The phantom works pretty good for drag, but again it's just 2 metal plates with a spring tensioning them that gets placed in the stock open diff and applys pressure to your spider gears... not the best for all situations, but that's just my 2 cents. *shrug*