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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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 Posted: Sun Mar 25, 2007 1:40 pm Post subject: oil/air seperator |
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Where does the oil/air seperator drain back hose connect to??
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Sun Mar 25, 2007 1:50 pm Post subject: |
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The 931 setup? Yes of course I have a picture of that..
It runs from the bottom of the air/oil seperator to the smaller (M14x1.5) hole just above-right of the oil drain -
http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=bdb3&.dnm=1d20re2.jpg&.src=ph
Some 924NA'ers have been using it for an oil temp sensor.
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Sun Mar 25, 2007 2:24 pm Post subject: |
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Thanks Smoothie
| Smoothie wrote: |
Some 924NA'ers have been using it for an oil temp sensor. |
Including myself....
I guess I will need to drill and tap a new hole... will it have to be below the oil line like the origional drain line??
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Sun Mar 25, 2007 2:59 pm Post subject: |
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Here's a diagram of the RoW 931 breather that I got from Jaap just recently -
http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=341f&.dnm=44fare2.jpg&.src=ph
It shows both the turbo drain (4) and air/oil seperator drain (2) going in below the oil line. -That suggests to me that any added oil drain should also go below the oil line, but I really don't know how important it is.
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Mon Mar 26, 2007 3:09 am Post subject: |
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Hmmm - On pondering this some more and given the 931 setup that appears to drain below the oil line, I was ready to guess that it's that way to keep the nasty blowby gasses from entering and possibly eventually causing blockage there due to a build-up of deposits from the interaction of the hot gasses, moisture, oil, etc. -Thinking that if the breather is clear and free-flowing, then the weight of a few inches of oil in the lines keeps the oil draining and the gasses going out the breather as they should.
-But- I just had a look at the "Turbochargers" book by Hugh MacInnes and he repeats several times throughout the book that turbos should always drain above the oil line and that below the line is a very bad idea.
-So we have the Porsche opinion stated by their working design that oil drains go below the oil line and the Hugh MacInnes opinion that's exactly opposite.
Can someone with the Corky Bell book take a look and see what his opinion is on this?
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Mon Mar 26, 2007 3:16 am Post subject: |
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Or maybe it's turbo drain venting that makes the difference - meaning that with venting (aka- turbo drain "breather"), you drain below the oil line. -And if there is no venting, then the drain has to be above the oil line? (The Hugh MacInnes book doesn't mention and doesn't show oil drain venting in its' illustrations.)
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox
Last edited by Smoothie on Mon Mar 26, 2007 3:20 am; edited 1 time in total |
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Raceboy
Joined: 01 Mar 2004
Posts: 2327
Location: Estonia, Europe
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| Posted: Mon Mar 26, 2007 3:19 am Post subject: |
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C.Bell says to route the oil drain line above oil level.
But Porsches design has additional oil catch tank on the turbo drain line that most OEM's and "amateurs" don't have.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold 
'84 924, turbocharged, sold.
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Mon Mar 26, 2007 4:03 am Post subject: |
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Well then, I think we wee detectives have got this one solved. 
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Mon Mar 26, 2007 12:00 pm Post subject: |
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Just looking at the diagram...
If there is oil caught in the trap, for it to flow down the tube to the oil pan you would think there needs to be no air trapped in the line...otherwise it won't drain... i.e the air has no way to escape ...
Here's where I started a little science experiment with some clear pvc tubing and some water....
I filled the sink with some water and got two pieces of clear tubing a 4mm and a 12mm diameter... I filled the tube with a little water at the top, blocked an end and submerged the other end in the sink...
With a large 12mm tube this make absolutely no difference, mabye there's a hole in my tube... but even when I blocked an end it still drained water.
With the 4mm tube it actually drained but it bubbled from the sink end... the higher the tube was raised the easier it was to drain, placing the tube in deeper water made the tube drain slower
My conclusion is : that the height of the trap and volume of oil in the trap make a big difference...
If the oil in the trap is enough to displace the oil below it will drain...
My other thought is along the lines of corky's rational, if there is a clear path from drain point in pan to atmosphere via the crank breather, then the drain line will not need to breath through the top or the bottom of the drain line...
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Mon Mar 26, 2007 2:33 pm Post subject: |
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The MacInnes book recommends an I.D. of 3/4"-1" for a turbo oil drain.
The OE 931 size is approx. 3/4".
[of course the air/oil seperator oil drain can be smaller than that]
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Wed Aug 22, 2007 3:49 am Post subject: |
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| Smoothie wrote: | | Can someone with the Corky Bell book take a look and see what his opinion is on this? |
Sure, since my wife just bought me his book for my b-day, and since I was just reading this post a few days ago, and just read his opinion on the subject, I'll post what he wrote:
| Corky Bell wrote: | excerpted from Maximum Boost, Chapter 4: Turbocharger Lubrication, pp. 44-45
Oil Drain System
Oil return line design is even more stringent than oil feed line design. Even the position of the turbo relative to the engine should take into account the requirements of positioning the oil drain line. The turbo must be positioned high enough to allow a downhill drain to the oil sump. The focus of the problem is that the oil seals in the turbo do not operate well if they are completely bathed in oil. Oil that has passed through the turbo bearings must be free to drain out quickly and without any serious restriction. Gravity is the only force available to rid the bearing section of oil, and gravity is, by all relative standards, a wimp. The layout of the oil drain system has a few fundamentals that should be observed:
- EXIT ANGLE FROM THE TURBO. Virtually all turbos allow a 360 degree rotation of the bearing section relative to the exhaust and intake housings. This is to permit a near-vertical downward alignment of the oil drain hole. Vertical is the ideal alignment, but where necessary, the deviation may be as great as 30 degrees.
- SIZE OF DRAIN HOSE. Where possible, a minimum inside diameter of 1/2 inch should be observed. It is frequently necessary to compromise the 1/2-inch ID, and this is permissible when other factors are favorable. For example, a 1/4-inch ID restriction at the fitting where the oil passes back into the engine may work just fine, but it is unlikely to work at all at the turbo end of the line. Keep in mind that no oil pressure exists after the bearing, and low-pressure flow requires much greater flow area for equal flow rates.
- ROUTING OF THE DRAIN HOSE. Ideally, the drain hose should swoop smoothly downward and arc gently over into the oil pan with no kinks, sharp bends, or rises. Equipment hanging off the side of the engine rarely permits the ideal to be achieved. Effort and forethought are necessary here. Keep the hose clear of heat radiated form the exhaust housing and manifolding. Insure that it is not subject to damage from road debris or is suitably protected. Special Requirements for Low-Mounted Turbos
Situations frequently dictate mounting the turbo so low in the chassis that gravity drain back to the oil pan is out of the question. While gravity is still the prime mover to get the oil out of the bearing cavity, a sump or small reservoir immediately below the turbo will be necessary to collect the oil, which can then be returned to the engine oil sump via a pump system. Perhaps the cleverest device in this circumstance is the oil-pressure-powered scavenge pump. The oil flow to the turbo is used to power a pump that in turn scavenges the oil sump. |
So, where are all those folks that constantly bellow about keeping things the way Porsche designed them??? It seems our illustrious Zuffenhausen engineers failed to observe two of the three fundamentals (size & routing) on this account!!!
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Wed Aug 22, 2007 12:50 pm Post subject: |
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Hmmm, my drain tube is much larger than 1/2 inches ID and takes a pretty mellow route back to the pan. . .
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Wed Aug 22, 2007 1:05 pm Post subject: |
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| Quote: | | my drain tube is much larger than 1/2 inches ID |
Right, sorry, was confusing it with the breather line for a minute there. However, it took Porsche 3 tries to get it right, the drain line comes off at a 90 degree angle from the bottom of the turbo (not 30 degrees as Mr. Bell recommends), it passes right by the exhaust (although clearly not a better route available), and was subject to clogging. My point is that some compromises were made primarily because the turbo was an afterthought on these cars to meet the higher performance expectations of the US market (at least according to the Porsche Buyer's Guide, wink, wink).
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