I cut and pasted this from Garrett's website. It applies to all turbos.
Oil Supply & Drainage
Journal Bearing Turbo
"Journal-bearings function similarly to rod or crank bearings in an engine - oil pressure is required to keep components separated. An oil restrictor is generally not needed except for oil-pressure-induced leakage. The recommended oil feed for journal bearing turbochargers is -4AN or hose/tubing with an ID of approximately 0.25. Be sure to use an oil filter that meets or exceeds the OEM specifications. "
Ball Bearing Turbo
"An oil restrictor is recommended for optimal performance with ball bearing turbochargers. Oil pressure of 40 - 45 psi at maximum engine speed is recommended to prevent damage to the turbocharger's internals. In order to achieve this pressure, a restrictor with a 0.040' orifice will normally suffice, but you should always verify the oil pressure entering the turbo after the restrictor in insure that the components are functioning properly. Recommended oil feed is -3AN or -4AN line or hose/tubing with a similar ID. As always, use an oil filter that meets or exceeds the OEM specifications. "
"OIL LEAKAGE SHOULD NOT OCCUR ON A PROPERLY FUNCTIONING SYSTEM IF RESTRICTOR IS NOT USED UNLESS THE SYSTEM PRESSURE IS EXCESSIVELY HIGH. "
Original site:
Oil & Water Lines | Turbobygarrett
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