Doing a custom Garrett T25 turbo install. I plan on welding a flange on a factory exhaust manifold. This will put the turbo oil drain about 1" above the oil pan bung. Does the turbo need to be a certain height above the oil pan bung for proper drainage, or is it fine as long as it's higher than the level of the drain-back fitting? The oil drain hose would be about 1" down, 90 degree right angle, 3" horizontal to the pan.
The bottom of the turbo just has to be sufficiently above the actual oil level in the engine. If you're still above the factory drainback bung in the pan you should be completely fine. The only thing you may still need to worry about is the angle of the drain tube. Oil drainback is gravity powered and the less inclined, the slower it will drain. At some extreme near-flat angle that will become a problem but i doubt you are there either.
I have seen a Dodge Magnum where the turbos were the lowest point of the car. (And did not have any ducting or even filters on the inlets)
More sanely engineered, I did a buncha work over the years on a twin turbo F-body that has an ingenious oil return setup. The turbos drain their oil into an oval reservoir under the torque converter (maybe 2"x1" oval by as long as a 4L60 oil pan is wide) which has a pair of -10 AN hoses running to a 2-stage dry sump style pump mounted next to the throttle body, which then has a single -10 hose running to the front of the oil pan. So it is functioning more or less like a semi dry sump evacuation chamber for the turbos.
45 degrees down angle is ideal.
Any lower than that and you may need a pump to pull the oil out the turbo (which is how the turbo mounted in the rear or lower than the engine block works)
In reply to Vigo :
Awesome - thanks for the info. The oil outlet on the turbo will be above the bung on the oil pan, and I think a very short 45 degree hose would make it.
In reply to Benswen :
The upside to a short run of return line is that it’s easier to clean out, but also easier to find that clog that killed your turbo.
A clogged drainback tube (unlikely imo as the passages in the center section are far smaller than the actual drain tube) would show up quickly as billowing oil out the exhaust. Once that restriction was removed the turbo would most likely resume functioning normally as forcing oil past the turbine seal doesn't necessarily damage it.
One way to improve your oil drainback functionality is to make sure that crankcase pressure is always low by enlarging the breather port(s) coming out of your valve cover. Blowby ALWAYS goes up with boost and many stock crank breather lines/ports can't flow enough to keep up with that without an increase in crankcase pressure, which slows turbo oil drainback and can also cause gaskets to fail.
In reply to Vigo :
Good point about blowby! But venting at the valve cover can bring its own problems, as on an engine with poor drainback to the oil pan, the additional venting up top can make enough internal wind to keep the oil up in the cylinder head. Audi five cylinder engines are awful for this, and they vent the crankcase at the crankcase!
This is where you see people running external drainback plumbing on insufficiently engineered engines (Nissan RB) and a lot of modern engines have dedicated drainback channels that run through passages in the block and in the oil pan to exit down below fluid level, to prevent blowby backup.
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