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Why did Porsche use 930/GT3 oil pumps ?

We all read that these are the best oil pumps, that they flow more, they scavenge more oil. All the numbers can be found in these forums.

But why did Porsche need a much better pump in the 930, compared to the SC ?
Is it to achieve a better lubrication of the engine's internals, or is it mostly for better cooling ?

My reasoning is, if an SC engine is already properly lubricated, why would the 930 need something better ?
The engine cases are pretty similar, and the oil pressure is limited anyway, so why would the 930 need a larger oil pump ?
On the other hand, if the 930 and GT3 have larger piston squirters, then there's more oil flowing into the case, the pump needs to flow more to feed the larger squirters, with a larger scavenge section. Then the larger pump would be mostly for extra cooling.

If that's the case, it would not make much sense to use a GT3 pump without using larger piston squirters.

Can some of the experts shed some light on this ?

I'm trying to understand which mods are needed to make the best use of a GT3 or 930 pump in an older NA engine ?
Or is it really an overkill to use a one of these pumps in an SC, 3.2 or 964 engine ?

Thanks,
Old 08-12-2016, 07:58 PM
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Thank you for posting this. I've had similar questions but hadn't bothered to post yet.

I can see why a turbo needs more oil flow capacity to keep the turbo(s) oiled, and also for higher volume oil squirters as suggested. But why is it "better" to have the higher capacity pumps in engines that don't have these features?

From my admittedly basic understanding of the relationship between fluid volume and pressure, and how the 911 oil pressure blowoff valves work, I would think extra volume provided by an engine that doesn't require it, would just result in extra oil dumping out the blowoff valve once the threshold pressure is reached. So yes, the engine would get more oil flow and higher pressure at lower RPM, but then flow and pressure would both max out as the relief pressure threshold is reached. And I'd think at higher RPM (at which generally the max pressure defined by the blowoff circuit has been reached), you won't get more flow or pressure anyway, so for race engines in particular, I am not clear on the value.

I'm curious to hear what others say about this ...

Scott

Last edited by stownsen914; 08-13-2016 at 06:05 AM..
Old 08-13-2016, 06:02 AM
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Scott,

The turbo has its own oil pump (driven by the camshaft), and its outlet goes directly to the oil tank, so it doesn't seem to change anything for the engine pump.
Old 08-13-2016, 06:44 AM
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It's a 914 ...
 
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Quote:
Originally Posted by tabasco View Post
Scott,

The turbo has its own oil pump (driven by the camshaft), and its outlet goes directly to the oil tank, so it doesn't seem to change anything for the engine pump.

I thought that was for turbo scavenge only? (turbo oil supply still from main oil circuit?) But I do not know turbos ...
Old 08-13-2016, 07:30 AM
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That's just turbo scavenge pump to get the turbos oil to the oil filter.
Bruce
Old 08-13-2016, 07:36 AM
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Correct, my bad. So there's extra oil for the turbo as well.
Old 08-13-2016, 10:44 AM
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For the 930 pump, from Porsche 911 Story, by Paul Frere, the piston cooling jets in the turbo went from 1.0mm to 1.5mm. So that is approximately 50% more oil onto the piston crowns.

It is a capacity (volume) issue, more volume at the same pressure. The pressure side is 8mm longer, and the scavenge side is 8mm shorter.
Old 08-13-2016, 06:22 PM
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Actually, it's 2 1/4 times more oil (.79 vs. 1.77), but the volume is the answer.
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Old 08-13-2016, 07:30 PM
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Thank you! Yes, area of the hole, not the diameter of the hole.
Old 08-13-2016, 07:57 PM
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The volume to pressure relationship of a gear pump is quite straightforward.

Assuming that there is no restriction of the inlet side of the pump the delivery will be proportional to the length of the rotor and the speed of the pump also assuming that tooth design isn't changed.

If the inlet of the pump is restricted then the pump will 'cavitate' and if this happened the impact on the bearings would be the same as surge during cornering on wet sump engines.

The pressure produced will be a function of the restriction on the outlet side of the pump - this does not take into account 'spill' caused by pump clearances/pump wear.

The viscosity of the oil also has significant effect. increasing oil viscosity will tend to increase low speed oil pressure but decreases flow though the bearings at all speeds.

As oil is the major cooling medium for the bearings maintaining a minimum flow is essential.

In a well designed system I would expect so a Delta T of around 30degC between the oil inlet to the bearing and the oil outlet from the bearing.

In general increasing flow and pressure will increase wear in the engine and damage the oil more quickly so a system that has just enough pressure at idle and a PRV set to sensible level to suit the pump flow is all that is required.

I would imagine that if you don't need the increased flow then reducing the scavenge would not be a good thing as it will leave more oil mist in the case.

This will increase parasitic losses due to windage and cause more heat to oil and potentially increase temperature.

(Dumping excess down a PRV will also heat the oil and the more you dump the greater the heating and hence parasitic loss.)

At the pressures and flows involved this may not be a big issue but notionally having a well matched system is always a good idea and as clearances will inevitably increase during the like of an engine some headroom is always provided.

Again in general increasing the delivery of the pressure pump is not necessarily a benefit.

I am not sure you can have too much scavenge - at least as long as you have enough settling time to de-aerate the oil and in general I think that oil tank capacities need to allow for around 2 minutes residence time unless there are other features to allow air separation.

It would be really interesting to try to rig up an engine on a test bed and run an external oil pump so changes in both the pressure pump and the scavenge pump could be made independently.

Last edited by chris_seven; 08-14-2016 at 12:46 AM..
Old 08-14-2016, 12:43 AM
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Chris, every time you post,its like going back to my University days listening to the Professor. Keep it up, I / we appreciate this empirical explanation.
Old 08-15-2016, 10:00 AM
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As load and speed increase, so does your required oil flow rate through a plain bearing.
So a 930 with, say, 50% higher loads than an SC or Carrera, would need more oil volume.
Likewise, a GT3 that sees 8000 rpm (and also makes more power) would need more than a 6000-6500 RPM 911.
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Old 08-15-2016, 10:35 AM
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They've been revving to 8,000 rpm since the 906. I think even the 935 could rev that high for qualifying. 935 used a 930 pump I believe? What about 956?
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Old 08-15-2016, 06:34 PM
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True that Porsche has been revving 911 race motors to 8000 and beyond since the mid 60s, long before the 930 pump came to be. Apparently the RSR and other racing variants in the early 70s used the same oil pump as the 908 (smaller than a 930 pump).

Bruce Anderson's book shows a few of the different pumps that Porsche put in its 911 race engines over the years, including the 908 and also some of the big 935 pumps. Looks like they had extra scavenging. See link below.

https://books.google.com/books?id=rOKlQ0ZzL6cC&pg=PA64&lpg=PA64&dq=908+porsche+oil+pump&source=bl&ots=ICmhKGeknj&sig=S-_jzngn9Z_GTUMpUi1iYY0dJiU&hl=en&sa=X&ved=0ahUKEwj0woXr8MTOAhWBGR4KHa4cBiEQ6AEILTAF#v=on epage&q=908%20porsche%20oil%20pump&f=false
Old 08-15-2016, 07:33 PM
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The pump

Quote:
Originally Posted by Flieger View Post
They've been revving to 8,000 rpm since the 906. I think even the 935 could rev that high for qualifying. 935 used a 930 pump I believe? What about 956?
The 935 engines are running the so called " big pump " as used in the 956 and 962.

The oiling strategy was different in general with out side oil lines on the engine housing.

Best reg.

Dirk
Old 08-17-2016, 12:54 PM
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