GT3 oil pump - Oil springs.

[Olsen911]

Gents.

After installing new GT3 oil pump in my rebuilt engine, i canīt figure out, what
length of springs i need to the Pressure release valve and the safety valve.

The engine is 1971 Mag. case with the Oil bypass modification and did run with the 3.2 oil pump with our host updated pressure springs-caps-piston set and with fine pressure numbers.

After disassembly i found that the pump had big scores in the bores, so decided to replace the pump and did get the GT3 pump.



So took the time to measure my springs:
The HORIZONTAL spring - oil SAFETY valve: 70 mm.
The VERTICAL spring - oil RELIEF valve: 83,7 mm. - should this not be 86 mm.??

After reading Walt Fricke about his GT3 pump Low Oil Pressure New 2.8SS i learned alot, (thanks) but couldnīt find the answers i was looking for.

So turned to the Ultimate Oil Pressure Relief Valve Thread and still donīt get it.

Here are the springs for the GT3 - and this is one huge spring:



As i understand, the incorrect spring lenght on the VERTICAL spring will affect the oil pressure, so would like to get the right one.

All help are appreciated.

Thanks - Cheers - Olsen911

[Flat6pac]

You have to use the one for the case design,
Bruce

[Olsen911]

Thanks - Bruce.

Will the 86 mm spring be the right one for the case design - Mag. case 1971.?

Cheers - Tommy.

[Olsen911]

Buuudaaaboooommm

[cgarr]

When the oil bypass is done to a mag case this is the kit that you need to install: The longer spring goes in the bottom:

Pelican Parts - Track Your Order

[Walt Fricke]

The late GT3 spring (the longest one) puzzles me a bit.

The things which matter about springs are the wire cross section (larger is stiffer), and the wire length (shorter is stiffer). Given that the tubular space the spring has to fit in, it looks like the spring diameter is held constant, and the cross sections are about the same. In addition, the coil spacing (turns per unit of distance?) looks about the same. Spacing seems mainly having to do with coil bind, and I'm guessing that isn't an issue with these springs (unlike valve springs, or some suspension springs).

In addition to rate (force applied to shorten a given distance), seat pressure, like with the valves, has to be in play.

For this later GT3 spring Porsche lengthened the spring, and also lengthened the spring's tube by extending it downward with that hollow tall cap. I am guessing that what was wanted was the same initial seat pressure (depends on spring rate and how much compressed at rest), and then a lower spring rate so the pressure piston could move down more and release more oil a bit faster (at lower oil pressures) than before. Or perhaps a slightly higher seat pressure, and then a faster increase in outflow due to the lower spring rate.

If otherwise everything on the late GT3s is the same - tube length and diameter is the same, openings are the same diameter, etc., I would suppose you could run this spring and its parts with this pump. But I don't know that. If I ever get my 2.8ss back together, perhaps I'll try this.

[tadd]

Has anyone ever used the complete GT3 parts kit (spring/really tall cap) on an early case using the GT3 pump?

I have a early 68 Al case that is going back together with a GT3 pump and the 'big' GT3 squirters. Will also be using center cam oiling along with the spray bars.

Have read all the threads on this...

Seems like a happy medium would be the longer spring of the later motors, but using the early cap which is 12 mm deep vs the 9 mm of the later motors.

[florent78]

nice post


I do the same modification:
996 GT3 oil pump with a 3.0SC 1983 crankcase (get the bypass by default)

same question
should I keep the original spring setting or should I get the GT3 spring for the oil relief valve and oil safety ?

thanks

[Walt Fricke]

Well, as you can see, I had the same question, to which there has been no answer. I was disappointed by the pressures of my GT3 pump during the engine's very short life (not as a result of oil pressure).

[tadd]

Walt:
Just to clarify.... what pressures were you seeing, and what spring/cap combo were you running?

I'm really tempted to go with the complete GT3 setup, but staying bone stock with both short springs is where I am leaning. At least until it is up and running. Given where the pressure assembly is located, it shouldn't be hard to change to experiment once in the car.

[florent78]

I will go for the full GT3 setup (my tuner recommend me to do it) more pressure is never an issue


will see ...

[Walt Fricke]

Tadd - I'd have to look at old posts, but to start with I was not getting 10 psi per 1,000 RPM, and the numbers were well below what I was used to seeing from the 930 pump, or even the SC pump.

I modified the external plug with an external screw and lock nut through it so I could raise the spring base inside the plug without taking anything apart, which also shimmed it up a bit, and I jacked it up some when I idled the motor in my garage. This helped, but before I could experiment much the motor blew up on the chassis dyno.

I was using the standard "regular" long spring and piston - the one which all 911s since the advent of the modification came along use, with that tubular insert to keep the spring from buckling and rubbing. I used those on my sand cast race motor cases. The GT3 pump was in a pressure cast early 930 case, which was made for the early six bolt crank.

I am not aware of any internal differences in this part of the oiling system casting/machined passages other than the modification to route oil from the pressure setting piston back to the pump intake, but I suppose there could be. The opening into which the excess oil from the pressure setting piston exits could be cast and machined at a different height relative to the whole long cylinder in the GT3 case. I kind of don't think so, but you can see where it is by looking at the plug inserted after machining with the flywheel off, and could compare where it is on our earlier cases with where it ended up on a GT3 case.

I would not use the short short/early spring, if that is the one you are thinking of. Nobody does that unless on an early engine without the modification, and using the early piston.

It would be convenient if the standard spring etc would work fine with the GT3 pump, because the GT3 spring system, with its extension, is not cheap.

[florent78]

do you think there is a correlation between your oil pressure issue and the engine blew up during dyno ?

[KTL]

In relation to the use-the-spring-setup-for-the-case-you-have rule of thumb, my one data point was the use of a 964 pump in a SC case. I used the same spring + piston setup in the engine that was used with the SC pump.

Before installing the 964 pump, the engine would crank out a solid 80+ psi on the mechanical VDO gauge running wide open at high rpms on the track. This gauge was fed from the port in the engine case near the thermostat. Same place the oil pressure warning light gets it's oil feed. When the 964 pump was used, I noticed the pressure seemed a bit lower than what I had experienced with the SC pump. I only ran the engine a couple of days before the engine got hosed. But I still recall that low-ish oil pressure.

Later on I recall seeing here on the forum someone mentioned William Knight indicated that if you run the 964 pump in the older engine cases, you have to be sure to use the little spring spacer or you'll have lower oil pressure. Tried finding where I read that but I just can't find it right now.

[Walt Fricke]

Kevin - you sent me to my PDF catalogs. I didn't realize that the 964s had illustration 13a, 964.107.532 spacer ring, to go along with the 911 part number for the piston, the 930 part number for the spring and guide tube, and earlier part numbers for the screw plug and washer.

Doesn't explain why this larger pump, unlike the Turbo pumps, needed more spring pressure. Nor why the GT3 has that longer spring with the screw base extension bit. But it seems it is prudent to shim up the spring if not using the spacer, and maybe more so with the GT3 pump if you don't go to those parts.

In the case of my motor's failure on the chassis dyno, it was not due to oil starvation. A J&E piston ripped in half at the wrist pin, and I believe that was due to a bad design - the web needed to be closer to the center on both sides, a number of guys had this kind of failure with this design of piston on race motors, and J&E subsequently changed the design.

I did discover what how poor the Glyco rod bearings from normal retail sources are (several discussions of that, and what to do about it), and had this not happened perhaps something even worse would have happened on the track well before I had any thoughts of a 100 hour or 200 hour rebuild. But there were no signs of heat in the rod ends or bearings, including the rod which held the piston which broke. Nor were there any signs (on the other five cylinders and pistons) of excessive piston heat, and the squirters (turbo diameter) were all in place. I have five very nice 95mm pistons cut for about 12:1 CR, with big valve pockets and slippery coated skirts which are probably of no use to anyone. The crank and five rods and five cylinders I can re-use, along with the block. The pump I need to get on the stick and send to Henry Schmidt to see if it can be saved, but the episode kind of put me off my feed.

[florent78]

from my read glycol seems have a good reputation / quality ...

for sure 100% perfect never exist

you prefer ACL ?

[Walt Fricke]

Search this forum on the subject - there is a lot there, and Gyclo's regular rod bearings are harshly criticized for bad QC, some posts with details of measurements.

The preferred rod bearing seems to be the Clevites made to fit our Porsche rods.

[prschmn]

Since the pressure relief circuit is in the end a simple hydraulic circuit I.E. spring force in Lbs
times area of the valve the only reason I can see that you'd see less pressure is that the pumps may have greater internal clearance. That's probably not much of an issue at 6K RPMs
Meaning the valve is always going to move at the same pressure.