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Optimizing oil pressure on rebuild?

Other than bearings, what else should one check for during a rebuild to optimize oil pressure?

My 930 motor runs great, oil pressure maxes out at 4 bar or slightly above on 20/50(which per WSM is fine as it meets > 50 psi at 3000 rpm). I have 2 bar at idle, 4 bar at anything over 3000 rpm and that's where it plateaus. I would kind of like "more" or 5+ bar if possible...

Read hundreds of threads, apparantly lots of folks show the same oil pressure, and like me, are fine. But 5 bar would be nice , especially as the motor is apart.

Motor gets tracked, cranks looks like new no damage. Old bearings look like new. Rod bearings with slight wear, but even now in spec (.002 clearance)...

Assuming that crank and rod clearance is in spec (they are), what else to check before buttoning it up?

I checked:

1) no missing oil squirters
2) no missing crank plugs
3) will disassemble oil pump (was going to have it polished to increase flow by Supertec, but after a phone conversation Henry suggested that these pumps should have PLENTY of pressure/flow if they aren't damaged. Same thing AA asscociates that makes the bearings said)
4) Pressure springs for oil reliefs were already replaced, as were the pistons, bores look fine (could there still be leakage past them??? Do a pressure test???). Shiming didn't make a difference
5) check tensioners to make sure they aren't somehow bleeding off pressure
6) check cam towers to see if bleeding off pressure (how?)
7) has cam restrictors in place
8) Yes, I checked with a manual pressure tester (read slightly higher, maybe 4.25 bar at 3000 rpm+)

The 930 pump supposed flows so much, that even at .004 clearance I have had builders tell me that they have seen folks with completely shot bearings and .004 clearance and no issues...

Any other places to "optimize" oil pressure? My idle pressure is fabulous... why the plateau at 3000 rpm? There are plenty of threads on here with people having the same findings, no issues. Still, I would love to see 5 bar hot. Mine, even ice cold goes immediately to 4 bar, and plateaus. Its like a switch gets thrown or a valve opens...

May still have a professional set of eyes look at the oil pump, but 2 builders have told me its almost never an issue (unless crap went through it...and nothing to suggest that so far)...

Last edited by bpu699; 09-22-2017 at 07:51 AM..
Old 09-22-2017, 07:45 AM
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looking for a problem that is not there is kinda like fishing for tuna in a swimming pool
Old 09-22-2017, 02:23 PM
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Make sure the nose bearing is in spec oil feeds into both ends of the crank to the rods.


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Old 09-22-2017, 03:02 PM
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Originally Posted by cgarr View Post
Make sure the nose bearing is in spec oil feeds into both ends of the crank to the rods.


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Interesting, will do...

Was going to use air to pressurize the relief Pistons make sure air isn't leaking by somehow...

The fact that the pressure hits a hard ceiling at 4 bar hot or cold really suggests to me it's a relief valve issue. But shimming didn't do a thing...

Why would the pressure plates at 3000-4000 or so and not linearly go up?
Old 09-22-2017, 03:38 PM
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Could be your sending unit or gauge. I peg the gauge when cold and get down to 0.8 bar at idle when over 100°
Old 09-22-2017, 04:04 PM
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Manually checked gauge, pretty much spot on. Dash reads 4 bar, manual gauge about 4.2 bar...

Again, plenty, but would love 5+ bar...
Old 09-22-2017, 05:37 PM
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Interesting. I was, and still may, start a thread on this topic.

My newly rebuilt 3.0 with the relief spring updates does a similar thing.

When warm the oil pressure will rise quickly to 60psi at 3K rpm. Then it seems to stay around 60psi until around 4K rpm then rises slowly after that. New sending unit.

Any ideas?
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Old 09-22-2017, 05:51 PM
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Check the bottom relief, pull the cap and make sure that plug as the spring guide post on it, that’s a longer spring and can get kinked in the bore without the guide.


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Old 09-22-2017, 06:38 PM
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I think your gauge is off. 2 bar at idle warm is awful high. Not in a bad way, but that's realllly optimistic. Most 911s struggle with just 1 bar at idle and really, almost zero oil pressure at idle is not even a need for concern. Porsche has changed their gauges and added spacers to the OPRV to increase idle oil pressure for north american users who panic.

It's not a Chevy.
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Old 09-22-2017, 06:54 PM
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Idle full hot, on the track is 1.5 bar minimum. Verified with 2 manual gauges installed on motor... it's not the gauge.

I keep reading threads about low idle pressure. Mine is stellar.

Pressure reliefs valves have the guide, and are shimmed.

I wonder if pressure is bleeding off the cam towers somewhere...

But again, if it were a bearing loss I would expect pressure to go up linearly from 2000 to 6000 rpm. Mine, like others posted on here, hits a hard ceiling around 4000 rpm at 4 bar and sits there. Eaxactly what I would expect from a pressure relief valve that had a weak spring... but it looks fine.
Old 09-23-2017, 06:30 AM
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What I am saying is that 1.5 bar idle full hot is higher than normal, and since your car maxes out at 4bar, perhaps something else is at work in that motor.

Did we talk about what oil you are using?
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Old 09-23-2017, 08:11 AM
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Brad penn 20/50.

I hear what you are saying, but my idle pressure is fabulous...no matter how I measure it.

Will look at it some more tomorrow. On day 2 of cleaning the case... Want it spotless...

Once that's done will double check the clearances, and disassemble to oil pump...

Does the relief piston make a perfect oil tight seal? Can it hold the correct pressure, but have oil leak around it? Would lapping the piston top to the case improve the seal?
Old 09-23-2017, 03:06 PM
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The relief valve is not on its seat when the engine is "running". The majority of oil pumped by the pump is bypassed and the valve is is a position of equilibrium to maintain the pressure required. Some oil can escape around the valve so there is a by pass hole drill in the case so the valve is not hydraulically locked.

If under running conditions you cannot increase the oil past 4b, there is something going on that is not normal. If you shimmed the valve solid, you should make 130- 140 PSI.

Pump spring too short, plug cap too deep, something is effecting this.
Old 09-24-2017, 09:01 AM
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Quote:
Originally Posted by Neil Harvey View Post
The relief valve is not on its seat when the engine is "running". The majority of oil pumped by the pump is bypassed and the valve is is a position of equilibrium to maintain the pressure required. Some oil can escape around the valve so there is a by pass hole drill in the case so the valve is not hydraulically locked.

If under running conditions you cannot increase the oil past 4b, there is something going on that is not normal. If you shimmed the valve solid, you should make 130- 140 PSI.

Pump spring too short, plug cap too deep, something is effecting this.
Didn't know that... but now confused...

I have owned 3 911s so far. 930 turbo, 911s, sc. NONE made 5 bar. Ever. The 911s had 110k miles, so figured bearings were worn. Shimming valve spring did squat. SC made about the same, shimming did squat. 930 has low mileage, shimming did squat.

On the 930, adding oil restrictions raised idle pressure. Top end pressure went up about .1 to .2 bar as a guesstimate...

Still don't understand how on can have stellar idle, yet peaks at 4.2 bar or so.

Clearly tons of folks have about 4 bar if threads on here are any indication.

If shimming can get you up to 140 psi, then why wouldn't everyone on here do it? Lots of folks with threads on here where they shim, and no change in oil pressure.
Old 09-24-2017, 09:34 AM
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^because that level of oil pressure is not necessary in the least for the engine to perform. And I think you are a little fixated on the "number" that defines oil pressure.

Adequate oil pressure is when the engine receives the flow that it needs, while all bearings in the motor are properly lubricated. What that exact number is varies somewhat.
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Old 09-24-2017, 10:07 AM
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^because that level of oil pressure is not necessary in the least for the engine to perform. And I think you are a little fixated on the "number" that defines oil pressure.

Adequate oil pressure is when the engine receives the flow that it needs, while all bearings in the motor are properly lubricated. What that exact number is varies somewhat.
Exactly.

If shimming made no difference to increasing your oil pressure, you need to find out why before you assemble your engine. Something is not normal here.
Old 09-24-2017, 10:13 AM
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only as an observation of comparison , I own an 88 carrera with 101 k miles. upon start up my oil pressure gauge goes right to 5 and is pegged there until an idle. i have never seen it below 2 bar while the engine is running. even on our hot days of 30 degrees celsius and a three hour run to the neighboring town. engine has never been apart.
Old 09-24-2017, 12:44 PM
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only as an observation of comparison , I own an 88 carrera with 101 k miles. upon start up my oil pressure gauge goes right to 5 and is pegged there until an idle. i have never seen it below 2 bar while the engine is running. even on our hot days of 30 degrees celsius and a three hour run to the neighboring town. engine has never been apart.
When ice cold, my cars pressure gauge shoots up to 4.2 bar and then immediately, like a switch was flipped, falls to 2.5 bar or so at idle rpm. I can add throttle, ice cold, won't go over 4.2 bar.

When full on hot, after a track day, I still get 4 bar hot at over 3000 rpm.

You would think that with thicker oil, cold, pressure would be sky high.

The fact that it happens so quick, really makes me think something "opens" relieving the pressure.

Will look at the relief springs again...

But this is exactly what I saw it's the 911s... that was 10 years ago, so my memory may be foggy...

Was planning to recheck all the bearing clearances today, but cleaning the garage/barn prior to reassembling the motor took forever. Swept, vacuumed everywhere, and ran a air filter.... the amount of mouse turds I saw everywhere was alarming... the mouse poisons spread all over the garage are clearly getting devoured...

Sent out the rods for resizing, and the bearings for coating at HM Elliot...

Ah, living in the country

Also, the amount of boxes and shelf space that a disassembled 930 motor takes is quite amazing...
Old 09-24-2017, 03:48 PM
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Had another thought...

I wonder if something on the intake side to the oil pump could effect pressure...

The solid line from the oil tank to the pump has the slightest dent in it... really small...

Wonder if that effects flow enough at high rpm to make a difference...

Will disassemble the oil pump tomorrow, time permitting...


Found more threads on here where people did a full rebuild, and didn't hit 5 bar...
Old 09-24-2017, 03:52 PM
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Had another thought...

I wonder if something on the intake side to the oil pump could effect pressure...

The solid line from the oil tank to the pump has the slightest dent in it... really small...

Wonder if that effects flow enough at high rpm to make a difference...

Will disassemble the oil pump tomorrow, time permitting...


Found more threads on here where people did a full rebuild, and didn't hit 5 bar...
I don't think the small dent would have any affect as it would be constant at any rpm and not prone to a fluctuation. I use 20/50 as well. I am thinking it may be the thermostat and something to do with the valves. once the thermostat opens you have a lot more capacity to feed to the trombone or cooler and quite a bit more capacity for the pump to push. I am just guessing and am by no means a Porsche mechanic. Its funny because I just spent the day cleaning my little shop also. no mice but the deer are thick this year. I am watching with interest. you will figure it out.
Old 09-24-2017, 04:35 PM
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