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chuck21401 · Joined: 20 Feb 2005 Posts: 532 Location: Annapolis, MD

I'm hopeful that I've been able to sort the electrical gremlins after replacing the wiring harness to the starter/alternator and the alternator itself. The car seems to be running well and staying cool with the new engine fan in place.

I did seven runs at the local PCA "test and tune" autocross the other day...and nothing broke.

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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

Fifty50Plus · Posted: Sat Apr 09, 2022 7:55 am Post subject:

New Avatar! Looking good.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

chuck21401 · Joined: 20 Feb 2005 Posts: 532 Location: Annapolis, MD

Couple of updates:

1. Oil pressure. After reading the recent thread regarding 931 oil pressure, I think mine is low. Warm oil pressure is 4 bar at highway speed warmed up and does not increase with RPMs. Idle warm oil pressure is between 1-2 bar.

The oil pressure gauge flickers a bit so I'm going to run a new ground wire first, then will check the oil pressure relief valve piston and spring. Finally I'll check out the cam oiler tube and elbow.

I recently changed the oil from 20W50 dino oil to 15W50 Mobil 1 synthetic and new filter and didn't see much of a change.

2. Slight boost leak. I'm getting a boost leak between the intercooler and the intake. This is the second time that I've replace the orange O ring (part #20 in the picture below). The first time the O-ring broke, the second time I nicked it when reconnecting the intercooler. I replaced the O ring by loosening the connection, removing the old O ring and slipping in the new one. I think that was part of the problem.

This time I emptied the antifreeze, disconnected everything and removed the intercooler. I figured now would be a good time to see how much work it takes to pull the intercooler and get to the valve cover for when I
check the cam oiler tube and elbow. I switched to water for the summer so don't have to worry about antifreeze going everywhere next time.

I am also seeing some oil in the intake track. It's not a huge amount, but it's there. The previous owner rebuilt the turbo, I'm guessing some seals somewhere are leaking? I don't think it's bad enough to pull the turbo....I'm not getting smoke at the exhaust if that's what I should be looking for.

While the intercooler was out I added some heat shield to the bottom. I'm not sure that it will make much of a difference but I figure that it can't hurt.

I was able to get everything back together again. I've found that there is still a slight leak between the intercooler and the intake. I can tell because new oil residue has appeared at the connection. It's not much, but it's there. The car has no trouble making 14-15psi.

I'm not sure what else to do, there isn't much of an adjustment in the mounting points.

[/b]

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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

It’s easy to see if the oiler tube is working..
Just look under the oil cap while it’s idling and you’ll see it squirting on a live right under it..
One of my under hood checks I very often look at..

That’s way more oil pressure than I ever saw my gauge read.. My car has been like “oil light on at idle when hot”, reading like 0.5, bar on 15-50 full synth, I believe the entire time I’ve owned the car..
But I do get my car very hot..

I decided a long time ago that if it was gonna blow it was gonna blow..
But back then I think replacement engines were easier/cheaper to come by factoring into that decision..

Same engine, haven’t touch anything inside ever other than taking the head off and putting it back on, and have done the oil pan gasket..

I ran it for quite some time @ 15psi in my early time with it doing almost nothing but hard test drives/boost pulls..
After I replaced the head gasket I almost immediately worked it back up to around 18psi and it’s never been lower than that since..
I set it to 20psi +- 1psi or so because that’s about where power stops increasing with boost as much.. Never set it lower on purpose..
I have logged up to 23psi and have seen my 20psi gauge buried further than that at other times..
Super high load pulls at 20+ in 4th up steep hills on purpose, right from bog spool to redline..

It doesn’t blow up..
Rips..

IF I actually have low oil pressure, it doesn’t care..
I’ve mostly run 15-50 Napa full synth with a shot of ZDDP additive, and most recently ran Rotella T6 in it for a couple of changes (hardest running)..
All good..

I wouldn’t believe anything that gauge says..
That oil pressure is fine anyway..
If your super concerned about it, rig a real oil press gauge to the same port the sensor is on..
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80 Turbo - Slightly Modified

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

Stock oil cooler, no oil temp gauge..

Have monitored my coolant temps extensively though and it doesn't even get close to coming up to stock temps there..

I don’t get to beat around a track at extended periods of time either..
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80 Turbo - Slightly Modified

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Chuck

I am wondering if there is a DASH number o-ring (non-metric) that is slightly larger that you could try. I am going to play around with this idea since I have the same inter-cooler.

You are using the spacer (19) so thats good.

Do you have the turbo drain vent system? I don't see it in your engine pics

I'll find some pics if you don't know what this is

Mike
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

chuck21401 · Joined: 20 Feb 2005 Posts: 532 Location: Annapolis, MD

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

My 80 doesn’t have any vent from the oil drain hose at all..
Just straight to the oil pan..

I notice no problems..

The 941 does have it..
The pipe coming off the head seems pretty wiggly..
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80 Turbo - Slightly Modified

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

My 80 was the same way and I only really had issues when overfilling oil. The 82 had some oil in the inlet and it had the system. I equated it to needing a turbo rebuild but that may or may not have been the cause. Should know soon once that car is back in the road
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

Beartooth · Joined: 05 Apr 2022 Posts: 212 Location: Roberts, MT

Interesting: my early '80 931 has the modified vent setup. I'm gathering that it wasn't included from the factory until '83 - definitely wouldn't have come on an S1 motor - so it must have been added later. Looks like somebody got the kit from Porsche back when: everything else looks exactly as expected for an S1 motor. If I'm understanding the discussion in that old thread, the modification ensures that crankcase pressure isn't pushing back against the turbo oil return, and may prevent condensation from affecting the vent and return line. Sounds like it might not be a critical modification, but it can't hurt.

In reading about turbos and oiling over the years, it seems drain-back is a big issue if not done right. I still don't understand why: you'd think pressurized oil to the turbo would overcome whatever's going on in the return line, but apparently a large return line feeding downhill back to the oil pan, and returning above oil level, is ideal if not necessary. The mounting of the turbo on the 931, being lower down on the motor, makes drain-back trickier. In more extreme cases, where the turbo has to be mounted below the level of oil in the pan, a dedicated sump and scavenge pump may be necessary. That's my understanding based on Corky Bell's book and various articles I've read over the years; I own a few turbo'd vehicles, but haven't done any custom turbo work (some day). My main thought is that there's more to turbo oiling than meets the eye, and modifications that look like they should work might cause big problems.
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1980 931 diamond in the rough

chuck21401 · Joined: 20 Feb 2005 Posts: 532 Location: Annapolis, MD

chuck21401 · Joined: 20 Feb 2005 Posts: 532 Location: Annapolis, MD

Couple of updates:

1. Bought a new gauge/sensors to measure intake temps before and after the intercooler. Plan to mount one sensor in the silicon hose before the intercooler and the other sensor in the stock IAT location. Still waiting for the unit to arrive, apparently they are made to order in the UK. https://www.race-parts.com/spa-dual-intercooler-in-and-out-temperature-gauge . I understand that these sensors will not be as fast as other set ups...but this is more for entertainment purposes, I'm not running EFI or anything. I think the temp reading could help me justify installing a large heat exchanger up front.

2. The existing temp gauge and new sensor cable will be repurposed to measure the water temp in the intercooler. What would be more interesting...water temp before or after the intercooler?

3. The silicone hose coming off the turbo keeps lifting off. This happened 2.5 years ago. I tightened the hose clamp and everything was fine since.

This time I tightened the hose clamp, but it popped off again after the next drive. I'm running 15psi.

Thinking that the hose clamp isn't up to the task, I installed at T-bolt and tightened things down....but same problem.

However this time the hose lifted high enough to intersect with the timing gear! So now the silicone pipe is ventilated....which isn't helpful when trying to build boost.

I've ordered another hose; it will be here later this week. So I'm trying to figure out what is going on. I noticed oil in the hoses as well as the intercooler. I've seen this before and the car does NOT smoke. But it makes me wonder if somehow the intercooler has become clogged?

I'm going to drain the antifreeze, remove the intercooler and take a look.

When I drove the car the boost seeming slow to build...then hit...seemed like there was more lag than usual. But then boost just fine....until the hose popped loose.

Pic 1 - looking down towards the turbo. T bolt installed at the turbo holding the silicon hose in place.

Pic 2 - here are the two 45 degree hoses and the 90 degree elbow reconnected after T-bolt installed.

Pic 3 - Here are the hoses after the run. The cam gear chewed a hole in the silicone hose. Not good! On the plus side, the T-bolt hit the factory bracket that holds the stock boost tube in place at the turbo....which prevented the T-bolt from hitting the cam gear and timing belt.

4. In addition to oil in the intake track....I'm getting external oil leaks. It appears that they are coming from the oil feed line that goes into the turbo mount. Parts 2&3 in the diagram below. But it's also possible that it could be coming from the other side...which means replacing the green o-rings? Ugh. Everything I've seen so far indicates that the turbo has to come off....unless you get lucky by tightening things up. I'm not that lucky.

The more I read the more I see that these things could be interconnected. It sounds like loose connections at the turbo, turbo mount, exhaust manifold, etc can lead to oil leaks. So I'll try to tighten things up first and then figure out what to do next if the situation doesn't improve.

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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

Cedric · Joined: 27 Aug 2004 Posts: 2614 Location: Sweden

Maybe you need to try to heat insulate the silicone hose, i dont think the pressure itself should be an issue, havent had any problems in my car. Or when we used these types of hoses at my preovious work on HD engines with 3 times the boost. Maybe its radiation heat from the exhaust manifold that softens the hose.

Could be a good idea to bench test the sensors with a hair dryer and see if they are slow or fast, could be good to know, it not always practical to need 40s full bost, at least not on the road

Measuring water temp at least before the intercooler would tell you alot about the capacity of the system, and how/if it stabilizes water temperature relative to ambient temperature.

Whats the state of the turbocharger, when was it rebuilt last time?
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1980 924 Turbo
www.instagram.com/garagecedric/

morghen · Joined: 21 Jan 2005 Posts: 8884 Location: Romania

You need a proper lip on the metal tubes that the silicone will be clamped on.
I had that issue on my old turbo as well, then i made some lips at the end of the pipes and roughed up the ends of the pipe with a coarse sandpaper.
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