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patkeefe patkeefe is offline
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Join Date: Apr 2004
Location: Bradenton, FL
Posts: 3,186
Turbo Oil Return...non-930 specific

I didn't want to clog up the turbo oil return thread, so I am starting this. The purpose is to examine the turbo return setups we use to get oil back to the crankcase or tank, whichever. In my case, I have an SC, originally retrofit with a BAE kit, now using 930 exhaust system. The old Rajay turbo sat much higher relative to the drain, which is in the left chain cover. Following photo is the current install. Drain outlet at the turbo is barely above the drain hole in the cover. There is no gravity drain.

The problem encountered is inadequate drainage from the turbo. This has been a problem since I first did the install. Muffler fills with oil, it leaks, etc.

In this current configuration, I drain into an AN-10 to a gear pump similar to a VW oil pump with an electric motor. Spec flow for this pump is 2.0 GPM (Electric Oil Feed and Scavenge Pumps).

I have previously determined the flow rate through the turbo to be 0.285 GPM. Oil was delivered to the turbo via an AN-4 oil line, unrestricted That test was conducted with the engine idiling, oil a bit warm, and pump inlet disconnected. I basically let the oil flow into a calibrated pitcher and timed it. On the surface, the little pump should have no trouble keeping up with this flow. BUT, it does. The muffler floods, car smokes.

Today, I went out and did the following setup to test the pump:

I am simply running oil through the pump. Oil temperature is about 38F. This setup, flowing through 3/8 barbs, results in a flow rate of 0.417 GPM. Not quite the 2.0 GPM advertised, but still more than the flow out of the turbo. So, this should work. BUT, it doesn't.

Next test is to go back out and try and standardize the oil temperature variances, to reduce any viscosity difference. Also, I will try and flow a known quantity of oil back into the chain cover through the pump, to check for restrictions. Lastly, I will try and flow oil back into the system with the engine running, to see the effects of crankcase pressure on the oil return.

I do recall the chain cover hole has a pretty clear shot back into the case, so I think there is a physical restriction. I do think the crankcase pressure may be part of this. Also, the flow into the turbo is excessive, I think. Hard to tell what the flow sj=hould be, because BW is not very forthcoming with technical support. I used to run a valve on the inlet to the turbo to tweak the flow. You can see the return to the cover in this last photo.

Patrick E. Keefe
78 SC
Old 11-20-2014, 09:12 AM
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