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Turbo Gravity Drain, does it work?

A number of you guys have built your own turbo systems for 911SCs and Carreras. I'm wondering how successful you've been with the discussed gravity drains to either a chain cover or sump plug. Is one recommended over the other for any preferred reason?

The project is a custom turbo system on a 3.6 in a 993 chassis. I don't want to have to integrate a 930 scavenge pump or an electric pump if I don't have to.

Old 05-05-2010, 07:06 PM
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I actually removed my electric scavenge pump and ran the drain to the sump to make room for my 993 AC condenser. So far so good, but I am careful to cool the turbo before shutdown and I use Mobil 1 to hopefully reduce coking risk.

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Old 05-05-2010, 07:32 PM
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I drain mine into where oil drain plug usually goes with -16 line. Had to restrict oil feed line down to -3 with garret turbo and I havent had any problems.
Old 05-05-2010, 09:23 PM
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I wonder if the supply line has more potental for colking after shut down as the oil might sit on top of the turbo.

The drain oil level should drop down to the level of the oil in the crankcase if plumbed into the bottom.

I like the idea of draning into the chain housing hoping for an air gap between the bottom of the drain line and the case residual oil level if the turbo is hung high enough.

Just my two cents.
Old 05-06-2010, 05:53 AM
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Jim if you can raise the turbo higher and drain into the timing cover I feel this is the best location. I been running this way for 6 years now and never looked back. As long as you have 1" above drain location you are good. I have been using -12 for the drain. I had it at the drain plug for a while but it would back up into the turbo's once in a while when in the twisties.
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Old 05-06-2010, 09:25 AM
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I know this is a picture of a twin setup but just to give you an idea. I also fabricate manifolds that bolt to the bottom of the turbo that gain you more clearance
Here is a drawing to give you an idea. Bacisally it is just a fabricated hard line and then AN from there to the final location.
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Old 05-06-2010, 09:48 AM
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Someone recently posted some pictures of a factory 934 or 935 showing the turbo drained to the sump. Also, didn't the earliest Turbo Carrera's have the sump drain as well without an additional scavenge?
My take on the drip tank to scavenge pump adaptation is that it was to effectively drain the turbo on shutdown and reduce latent heat oil coking. For my use, sacrificing the drip tank and scavenge pump for an effective AC seemed worthwhile until my next rebuild at which point I will likely go to a mechanical scavenge system without sacrificing my cam sensor. However, I don't track the car or even AX at this point which I think would have a significant impact on the decision process.
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Old 05-06-2010, 11:27 AM
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Originally Posted by GJF View Post
I had it at the drain plug for a while but it would back up into the turbo's once in a while when in the twisties.
This is exactly the kind of thing I was thinking, especially sicne the turbo is located behind the engine so the gravity drain effect would be working against acceleration. I also plan of trying a ball bearing turbo on this project since they don't require oil gally pressure to sustain bearing float, apparently you can orfice them down significantly without damage.
Old 05-06-2010, 04:56 PM
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When Jerry Woods rebuilt my 3.5 he ditched the scavenge pump and fabricated a a custom sump cover.They were talking about making a small run for sale. Don't know if that happened.
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Old 05-06-2010, 08:52 PM
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Quote:
Originally Posted by sjf911 View Post
Someone recently posted some pictures of a factory 934 or 935 showing the turbo drained to the sump. ...
There is a picture of a 1993 3.6 Turbo hill climb motor somewhere. It did drain into the case bottom drain hole.

However, that was not directly from the turbo. It was from the scavanging pump and instead of dumping it back into the oil tank unfiltered as on a 930.


Can we tip the turbo and how much to drain into the chain housing?
Old 05-07-2010, 06:14 AM
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I have run it 3 different ways 1st was drain into the cover worked ok but did not real easy to make leak proof. I then tried into the sump plate which works pretty well but on my stock sc oil pump it did not seam to scavange enough at idle. Then I tried it with my rebuilt engine with the supertec modded sc oil pump and it worked fine at the sump[. I used that for a year but could not get over the fact the oil line was the closest thing to the ground so I switched to a stock 930 scavange pump. that seems to be the best solution for my application it works worry free for me though my car is not a 500 hp monster nor is it a 930 it is just a 3.2 ss sc based engine with efi and a k27-7200 if that matters
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Old 05-07-2010, 12:09 PM
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Quote:
Originally Posted by Jim2 View Post
This is exactly the kind of thing I was thinking, especially sicne the turbo is located behind the engine so the gravity drain effect would be working against acceleration. I also plan of trying a ball bearing turbo on this project since they don't require oil gally pressure to sustain bearing float, apparently you can orfice them down significantly without damage.
Remember that while accelerating, the oil coming into the turbo is pressurized and that liquids don't compress. As long as you are running rigid lines, the oil is not at risk of backing up, as the turbo actively has its oil evacuated by the incoming flow. Gravity drain only matter when the car is not running, thus why the factory added the tank...since the scavenge pump isn't running when the car is off, it gives the remaining oil in the turbo at shutdown a place to go. Even the scavenge pump motors need to utilize gravity to pull oil out of the turbo when not running.
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Last edited by kenikh; 05-07-2010 at 02:15 PM..
Old 05-07-2010, 01:07 PM
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Quote:
Originally Posted by kenikh View Post
Remember that while accelerating, the oil coming into the turbo is pressurized and that liquids don't compress. As long as you are running rigid lines, the oil is not at risk of backing up, as the turbo actively has its oil evacuated by the incoming flow. Gravity drain only matter when the car is not running, thus why the factory added the tank...since the scavenge pump isn't running when the car is off, it gives the remaining oil in the turbo at shutdown a place to go. Even the scavenge pump motors need to utilize gravity to pull oil out of the turbo when not running.
All wrong, back to turbo 101
Old 05-07-2010, 05:59 PM
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All wrong, back to turbo 101
It appears clear that my understanding of the 930's turbo oil system is flawed. Unfortunately, your post didn't add anything other than a little sting to my pride. I'm a big boy - happy to take it.

Maybe you could post a little info to point me to where I went wrong? This would help so I can delete my previous post in good conscience, so as not to mislead others.

This is why no matter how noob the question in the engine rebuilding forum, I always respond in great detail...there's no advantage in sending someone away without the right info...one day they may get a chance to pass it along, too.
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Old 05-07-2010, 07:40 PM
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Harold, thanks for the input, proves that back-up under acceleration is not an issue, but I do wonder if Jerry incorporated a "trick" like a standoff tube in the center of the sump plate which is near the scavenge pump orifice. You happen to have had the sump plate off by any chance?
Old 05-07-2010, 08:00 PM
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Ben, I believe I had seen you post a WTB ad for a scavenge pump and this is what got me wondering if the gravity drain format had issues. You never seemed to mention a problem earlier on.

So it works for some, but not for others. Perhaps there are small variences which cause go/no go.
Old 05-07-2010, 08:05 PM
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Mine feeds back into the oil sump plug of my carrera, has been that way for about 3 years without a hitch. I maybe wrong here but I think you're safer running a more modern ball bearing turbo as the oil supply is greatly reduced so there will be much less oil to scavenge than a K27 (also less very hot oil re entering the sytem)... I imagine you'll be looking at something like a GT40, there is a 993 turbo thread in here somewhere and someone has talked about their, very successful, conversion.
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Old 05-07-2010, 08:23 PM
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Quote:
Originally Posted by Jim2 View Post
Ben, I believe I had seen you post a WTB ad for a scavenge pump and this is what got me wondering if the gravity drain format had issues. You never seemed to mention a problem earlier on.

So it works for some, but not for others. Perhaps there are small variences which cause go/no go.
My issues were purely idle and restart as oil would pool and back up into the turbo. The problem for me has gone away with the scavange pump being added. but keep in mind my oil pump is not what a 930 pump is so that may be why dirrectly feed into the drain was not as good?
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Old 05-08-2010, 04:13 AM
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I haven't had much of an issue with Ben's old setup I get a little smoking when I start it up after sitting for a month or so but that is it
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Old 05-08-2010, 04:29 AM
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Quote:
Originally Posted by kenikh View Post
Gravity drain only matter when the car is not running, thus why the factory added the tank...since the scavenge pump isn't running when the car is off, it gives the remaining oil in the turbo at shutdown a place to go. Even the scavenge pump motors need to utilize gravity to pull oil out of the turbo when not running.
Yup. I typically have 7 ounces of oil in the catch tank after a good, long shutdown.
If one just runs a line from the turbo to the sump, that oil has to go somewhere. Will it back up into the turbo?

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Old 05-08-2010, 05:56 AM
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