here is something Scot posted: for those that havent read it
-Advancing the Intake cam, and Retarding the Exhaust cam will open up the overlap a bit. This allows the cylinder to fill sooner due to the intake valve opening sooner, which can sometimes be advantageous in a turbocharged engine. This also helps to improve the idle quality since the Intake cam has a larger impact on the idle than the Exhaust cam does. Or, the exhaust cam can be retarded more than the intake cam, as in a -1 -4 setup. Both cams are retarded in this situation, but the exhaust cam is moved more, increasing the overlap.
Ultimately this is one of those cases where a dyno comes in real handy. You move the cams around until you find the right combination. Unfortunately theory only gets you so far, and practice makes perfect..