How big shaft clearance should has a turbo with ball bearing tall?

The Garrett full ball-bearing turbo is designed to have clearance between the bearing cartridge and center housing for hydrodynamic damping in addition to the internal clearances of the bearing cartridge itself. Hydrodynamic damping uses the incompressible properties of a liquid (oil in this case) and the space around the bearing cartridge to dampen the shaft motion of the rotating assembly. When the turbo is new, or has not operated for a long period of time allowing most of the oil to drain out, the rotating assembly will move more in the radial direction than a typical journal-bearing turbo because there is no oil in the center housing. This condition is normal. As long as the shaft wheel spins freely and the wheels don’t contact their respective housings, the assembly will function properly.