Basic Fluid Dynamic Question (Oil Return on Turbocharged Car)

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propav8r
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Ok-I'm actually looking to settle an argument on another forum. I have turbocharged my 1979 Volvo 240, and converted to a later style motor. Instead of drilling and tapping the boss in the block for my oil return to the oil pan, I welded a 1/2" NPT bung into my oil pan. The approximate inner diameter of that bunt is 5/8".

The oil drain outlet from the turbocharger is also approximately 5/8" inner diameter, giving more or less the same hose diameter all the way back to the oil pan from the turbo drain.

Here's the argument though. The engine is canted approximately 15° over to the exhaust side, meaning that the oil return has a slight upward section before it dumps into the oil pan.

My line of thinking is that the oil level in the drain hose will back up some, but only to the level of the line outlet. Others seem to think that it will cause major drain issues, which I just don't see.

I should probably mention that turbo oil drains don't see only pressure, only flow. The turbo itself is fed from a -4AN line with pressure varying from 4 bar to 1.5 bar, but once the oil has gone through the turbo, it loses it's pressure.

Can anyone more well versed in fluid flow than myself help me answer the question? I've included a pictoral for further explanation.

IMG_3677.jpg
 
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So what would a garden hose do in the same situation? Allow flow and when the flow was removed the only fluid left would be even lower than your blue marker. When your engine is making boost, the crankcase will get more blow by and increasing the crankcase pressure a little bit. This might cause the drain level to rise up a bit (no more than 1/2 an inch) but the fluid will still flow.

It is not ideal but with your turbo mounted higher, you won't have a drainage issue. FYI about a pint of oil will flow through your turbo per minute. I have added turbos to three separate vehicles.
 
That was my line of thinking.

As for pressure in the crankcase, there shouldn't ever be too much-my PCV isn't recirculated. I'm just using a road draft tube instead. Not too friendly for the baby seals, but we've got too many of those already. :smile: