A turbocharger's center bearing spins a shaft at 150,000-250,000 RPM while exhaust gases on one side cook the housing to 1,600°F. The only thing keeping that assembly alive is a continuous river of oil — and the routing of the feed and drain lines matters as much as the oil itself.

The feed line taps pressurized oil from the engine's main gallery, usually via a banjo fitting at the block or oil filter housing. Critical design rules:

• Restrictor sizing: Ball-bearing turbos need a restrictor (typically 0.040"-0.060" orifice) because excess pressure forces oil past the seals and into the exhaust — that's where the famous "blue smoke on startup" comes from. Journal-bearing turbos run unrestricted, needing higher volume to support the hydrodynamic oil wedge.
• Line routing: Feed lines must drop into the turbo from above, never loop below the center housing. A low spot becomes a coke trap when heat-soaked oil carbonizes after shutdown.
• Material: Stainless braided lines with PTFE liners survive the heat. Rubber hose near the turbine housing will harden and crack within months.

The drain line is where amateur builds fail. Oil enters the turbo pressurized but must exit by gravity alone — and the oil leaving the bearing is foamy, full of entrained air from the spinning shaft. Rules:

• Diameter: Minimum 5/8" ID, ideally 3/4". Smaller drains back up and pressurize the center housing, blowing oil past the seals.
• Slope: Continuous downhill at 30° or steeper. No horizontal runs, no upward bends.
• Sump entry: Must terminate above the oil level in the pan. If submerged, hot oil can't degas and crankcase pressure pushes back up the drain.

Real-world example: The Garrett GT3582R on a built 2JZ specs a 4 AN feed line (-4 with 0.045" restrictor for the ball-bearing version) and a 10 AN drain. Builders who downsize the drain to 8 AN to clear an oil pan often see smoke from the exhaust after a few thousand miles — the center housing pressurizes and pushes oil past the turbine-side piston ring seal.

Rule of thumb: Drain line cross-sectional area should be at least 4× the feed line area. A -4 feed (0.049 sq in) wants a -10 drain (0.27 sq in) minimum. If you can't fit gravity drainage, you need a scavenge pump — there's no middle ground.