There were many customers who asked us if their turbos require a restrictor? Here's a brief summary of our suggestions and practices. The function of the oil restrictor is an adjustment of the oil pressure feeds into the bearing system.
We recommend oil pressure of the ball bearing is 40 – 45 psi at maximum engine speed to prevent damage to the turbocharger’s internals. To achieve this pressure, a restrictor with a 1.0 mm~1.5 mm orifice will normally suffice. But you should always verify the oil pressure entering the turbo after the restrictor to ensure the components function properly. we recommend oil feed -4AN line or hose/tubing with a similar ID. As always, use an oil filter that meets or exceeds the OEM specifications.
You may probably hear journal bearing turbos do not require a restrictor, however, a restrictor, ensures better lubrication and keeps the components separated by an oil hydrodynamic film to prevent the metal components from premature wear and ultimately a failure, greatly reducing the chance of oil leakage and smoke coming out of the exhaust, consequently prolongs turbo life , so that most of our turbo install kits come with oil restrictors whether the ball bearing or journal bearing type. The GT B.B series we applied with 1.0 mm and the TD series (Ball Bearing and Journal Bearing) comes with a 1.5 mm orifice.
BE CAREFUL OF OIL DRAIN DIRECTION
Generally, the larger the orifice of the oil drain, the better. Thus, we usually offer -8AN or -10AN size comes with an install kit. If yours, try not to have an inner diameter smaller than the drain hole in the housing as this will likely cause the oil to back up in the center housing. Speaking of oil backing up in the center housing, a gravity feed needs to be just that! The oil outlet should follow the direction of gravity +/- 15° when installed in the vehicle on level ground. If a gravity feed is not possible, a scavenge pump should be used to ensure that oil flows freely away from the center housing.
When installing your turbocharger, insure that the turbocharger axis of rotation is parallel to the level ground within +/- 15°. This means that the oil inlet/outlet should be within 15° of being perpendicular to level ground.