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Rob 930 Rob 930 is offline
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Join Date: Dec 2002
Location: Seattle
Posts: 661
Originally Posted by gumba View Post
There seems to be a difference of opinions between mechanics on how well the stock scavenge pump system works. JW didn't think they worked that great, choose to ditch it and go with a gravity return at the time of the rebuild. The JW sump plate is approximately 1.250" deep at it's lowest point with the return line and drain plug on the side. In your photo you have stuff lower than that on 4 sides so I don't see the sump plate being an issue. Yet, I've seen some awfully weird offs at the track, so to each his own.
I'm going this route for it's simplicity, and I have a Carrera oil tank I'd either need to modify or swap out for a turbo tank to use the stock system.
I'm not the all-knowing expert in this, but I've never seen a properly maintained stock 930 scavenge system fail to operate correctly. And I've heard of all kinds of problems -- and have experienced them first hand -- with gravity return systems that didn't work right. It's my understanding and experience that a stock turbo in a stock location may *not* drain properly to the sump by gravity only -- there's not enough fall. So the reason for my post was only to ask why it's necessary to "fix what ain't broke." Granted, gravity is "simpler" and if you have a such a system that is engineered properly and proven to work under all conditions, then that's great. But getting there has its drawbacks too -- a specially machined sump will cost a bundle - and it will hang down and increase vulnerability to undercarriage hits. And will it work without raising the turbocharger? Doing so is a big deal.

Gumba, you pointed out that other things like exhaust may hang low and get damaged as well, which is true. But the worst possible situation is to scape off your oil sump and immediately drop all the oil. If you have other extenuating circumstances, such as missing some of the stock infrastructure (pump, cam drive, lines, and spigoted 930 oil tank), then the balance may shift to exploring other options. You may fall into this category. But for those who have the hardware and infrastructure available, why would anyone want to do it?

My understanding from discussions with Bob Holcombe long ago is that for Garrett (or other non KKK turbos that flow a greater volume of oil through the bearing), the stock scavenge pump *may* have issues keeping up. But the potential for such a problem only exists at idle. That's why for a Garrett setup, he suggested an overflow and vent line from the top of the drip canister to the right side chain cover. I never confirmed that any oil ever flowed down that line, but it was an easy and inexpensive addition to provide a margin of safety. And I never experienced any scavenge issues under any street or track conditions.
Old 11-05-2014, 09:48 AM
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