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KTL KTL is offline
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I wouldn't do the bypass w/out changing the pump. The routing of the oil, size of the bores and the tipping points of when oil is relieved is all factored into the size/capacity of the pump (both pressure side and scavenge side).

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Old 01-09-2013, 08:32 AM
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I have built 2 engines with the early pump + bypass mod and no problem at all.

To improve oil pressure at idle, Porsche increased the size of the pressure pump gear and at the same time reduced the size of the scavenge pump gear a like amount so thus both pumps could still be in the same size housing.

Porsche did the bypass mod to help drain the crankcase with the reduced scavenge pump capacity of the later pump.
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Old 01-09-2013, 08:38 AM
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KTL KTL is offline
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If the pressure pump capacity is increased and the scavenge side capacity is reduced, doesn't that put more oil in the sump at some point?

My thinking in saying not to do the bypass w/out changing the pump was based on:

If the oil bypass mod is putting more oil on the pressure/inlet side of the pump, then it would make sense to have a pump that can take advantage of that.

If the oil bypass mod was intended to reduce the amount of oil in the sump by not allowing the bypass to be directed to the sump you want to have a pump with a reduced scavenge capacity, no? However, if the bypass mod is being fed by an early pump that is scavenging more oil than you want it to, is there the potential for the pump venturi to be uncovered and suck air into the system? Or am I over-analyzing the differences between the early and later pump capacities?

I don't like fiddling with things that alter pump capacity w/out fully understanding the outcome. So that's why i'm being cautious.
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Last edited by KTL; 01-09-2013 at 09:00 AM..
Old 01-09-2013, 08:58 AM
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Kevin - I think you are overanalyzing.

As long as there is plenty of oil in the tank, it doesn't really matter if the scavange pump sucks air. I think it does some of that no matter what anyway. The tank serves to de-aerate it (not that air is good, but there is time to get rid of it before it gets to the bottom of the tank). And the venturi system came along as a modification for the 3.0 liter motors. The 2.7s didn't have that - remember the flat sump plate and all that?

It is only the oil which is bled off in order to keep the pressure where it belongs which is bypassed back into the pump inlet instead of into the sump. This amount is that much less oil which the tank needs to supply at that point.

If the system at a given RPM and oil temperature and so on is passing enough oil that the pressure is not opening the pressure setting (bypass) piston, then none is bypassed, and the engine is operating the same way as the older system did - only the oil which passes through bearings and squirters (like the cam's, if no pistion squirters) ends up in the sump.

And Cupcar points to his experience as well as theory to validate this.

I see no disadvantage in doing the bypass mod, even without changing pumps. By reducing the windage and the work the scavange side has to perform, you reduce parasitic loss by some amount. Maybe not enough to worry about, though. The questioner's experience with the long life of his old 2 liter motor suggests this is not a must do item for a completely stock rebuild of that overdesigned early model.

If it were my motor, I think I'd do it - because it is something a guy can do himself if he has a tap for a plug, and can figure out how to get his drill bit started at an angle into the inside of a cylindrical passage.

Low oil pressure at idle can be scary. The first 911 I drove - an early '70s T - with a notion to buy it had that. I drove it around with the owner/seller in the passenger seat. Stopped up in the mountains, and looked at the OP gauge. Wow, said I - is this normal (it read almost zero as far as I could tell, though no warning light was displayed). Gosh, he said - I don't know. I babied the car back to where we had started, and said I'd call him if interested.

Now I realize that this is pretty normal for a 911 of that era, and that it is oil pressure at operating RPMs which really counts, and it builds quickly. The guy's motor was probably just fine.

I note that with the advent of the SCs Porsche changed from a 10 bar gauge to a 5 bar gauge. I have always supposed this was for psychological purposes - the needle moves twice as far for a given pressure change. So the idle pressure won't look quite so low.

I can't recall if, when adding the piston squirters, the pressure side of the pump was increased? By the mid-70s, half way through the 2.7 era, with all the problems that motor had in its USA configuration, I suppose Porsche figured it had to do something and changed the pressure side of the pump to put out more oil. But that wasn't a problem with the 2.0s, was it?
Old 01-09-2013, 09:15 PM
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KTL KTL is offline
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I understand that the scavenge pump sucking air isn't terminal. But it seems that its always been a desire to keep it from occurring and that's why the uber pumps like the GT3, 959, 935 had the additional scavenge pickup. Granted these are for racing-like applications so a street car shouldn't be experiencing the type of condition that uncovers the rear of the pump?

I know what you're saying about the bypass function. It's the overpressure oil that is being managed by the bypass- goes back into the pump to feed bearings instead of being "wasted" by bleeding it off to the case sump.

I guess it just seems logical to me that we'd want to keep a suitable supply of oil in the sump to keep the scavenge being fed? I know a dry sump system is intended to minimize oil residing in the case. But it seems to me that you want a balance of pressure & scavenge pumping?

I think the pump was the same from '69 up until the bypass alteration in '76. So, no, I don't think the pump changed when the piston squirters were added. The pump looks like it was a little smaller pre '69

I agree low pressure at idle intuitively concerns most people who generally understand the workings of the engine. I'm sure people feared the 0 on the gauge and thought there was a problem. Like you said, a few changes were made by Porsche over the years to get people to stop worrying about low oil pressure problem that didn't exist:

1. Changed the scale on the oil pressure gauge like you said.

2. Changed the pressure at which the low oil pressure warning light came on. Originally it was activated 0.5-0.7 bar and it was reduced to 0.3-0.5 bar.

3. Changed where the oil pressure reading was taken. They moved it from engine case near t-stat, rearward to cam feed line right of fan. Incidentally it moved back to the t-stat area on the 964 3.6 (no t-stat by the way....)

4. Changed the cam line restrictors to be smaller. What that did is improve low rpm oil pressure seen at the gauge (a "political" fix), activated the piston squirters sooner (good), however took away some oil from the cam towers (bad).

Pumps pictured below are from top to bottom:

pre-69 (aluminum)
69-76 (3 rib magnesium)
76-77 (4 rib magnesium 2.7 bypass mod)
missing is the 78-83 (SC 3.0 aluminum 4 rib)
83-89 (Carrera 3.2 aluminum 4 rib with built in strainer) Note that some of the 3.0 engines could have a 3.2 pump since there were some SC engines produced with the later Carrera case (no sump plate)
89-98 (964, 993 magnesium or aluminum depending on year)



Missing from the picture are the super duper pumps- 930, 996 twin turbo and GT3/GT3R
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Last edited by KTL; 01-10-2013 at 08:42 AM..
Old 01-10-2013, 07:02 AM
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Thanks also to Cupcar and Walt for that input. I think I'll go ahead and do it. Certainly won't hurt, and might possibly help a little.

The size of the two pumps was changed in '77, so the early pumps run the piston squirters just fine. Probably the change was more to ease complaints about the low-pressure light at idle than for any real oiling problem. But this was follwed in early '78 by a mysterious sudden flurry of dead 3.0 motors. I had an acquaintance with one of the very first of those. His motor expired when the car was just weeks old. The dealer exchanged it and the dead core was shipped back to Germany for examination. That case and others lead to the re-design of the scavenge pump pickup, as they realized when driven at high speed for an extended time all the oil was winding up in the case and the pressure side was getting starved. Symptoms were power loss and an alarming increase in oil temp as the case increasingly filled with oil. Rational guys backed off until things normalized. But a few like the guy I knew (hot-headed leadfoot) were just determined to go flat out and ignore the warnings until something broke.
Old 01-10-2013, 07:13 AM
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Kevin,
Thanks for the pump pictures. Nice evolution.

Three corrections though (I think, from memory, and if someone looks up the service bulletins and corrects me, I'll take it like a man!).

The second pump was used '69-'76

The third pump down is the one that appeared in '77 and was used through '78 or maybe '79.

The fourth pump down is the one that appeared around 1980 (?, whenever the one above stopped) to correct the problems experienced by the early 911 SCs and continued through '89

DG

Last edited by Daves911L; 01-10-2013 at 07:26 AM..
Old 01-10-2013, 07:23 AM
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KTL KTL is offline
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Yeah I can't count...... 5 pumps and 6 descriptions doesn't add up!

I goofed on the pump transition from '76 to '78. I'll make that correction.

However the fourth pump down is indeed a Carrera pump. What you're thinking of is the separate venturi screen that Porsche added to the SC.

Here's the venturi screen that slips over the pickup tube. The later pump has the screen fixed on the tube



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Old 01-10-2013, 08:37 AM
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I look at it this way it is an Ohm's law thing where pressure and flow are balanced in a system where the resistance of the lubrication galleries remains constant, the resistance of the relief valve is variable proportional to flow and the flow from the pump varies proportionally with engine RPM.

As engine RPM increase pressure pump flow increases and this additional flow is diverted to the crankcase by the variable resistance of the relief valve but the flow through the lubrication galleries will remain constant.

Thus, I think the best balance of pressure and scavenge pumps is when the crankcase is completely empty and the tank as full as possible.

This means to me that the scavenge pump can't bee too large (unless the oil tank is too small to hold the total volume).

For the photo gallery here is picture of late GT3 pump versus 964 pump. The GT3 pump has an pickup to help during chassis braking:



And the mother of all pumps, the 3 scavenge section 962 pump. Note in this engine one of the camshaft housing drains is omitted and the hole in the side of the crankcase is used as an additional scavenge pump outlet back to the oil tank. Note the long pickup at what would be the front of the engine in a mid engine car to help with pickup under chassis braking.

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Last edited by Cupcar; 01-10-2013 at 09:09 AM..
Old 01-10-2013, 09:07 AM
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Quote:
Originally Posted by KTL View Post
....

Here's the venturi screen that slips over the pickup tube. The later pump has the screen fixed on the tube

In the 901 pump engines I built I also used this screen to help lower sump volume as much as possible.
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Last edited by Cupcar; 01-10-2013 at 05:13 PM..
Old 01-10-2013, 09:12 AM
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Great stuff - makes me want to get on the stick and try to sell the pre-69 cast aluminum pump I have as surplus. Kevin's collection far outpaces mine, at least for pumps not in motors.

And I'd always wondered about the extended pickup on the 962 pump - it hadn't dawned on me that those were mid-engine, that braking affected things, etc. My 2.7 could brake at about 1 G, while accelleration was at best about 1/3d G. Though might the 962s have had accelleration which equaled their braking?
Old 01-10-2013, 01:29 PM
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Quote:
Originally Posted by Walt Fricke View Post
Great stuff - makes me want to get on the stick and try to sell the pre-69 cast aluminum pump I have as surplus. Kevin's collection far outpaces mine, at least for pumps not in motors.

And I'd always wondered about the extended pickup on the 962 pump - it hadn't dawned on me that those were mid-engine, that braking affected things, etc. My 2.7 could brake at about 1 G, while acceleration was at best about 1/3d G. Though might the 962s have had acceleration which equaled their braking?
I bet the 962, depending on the aero down force of the chassis, could go as high as 3 maybe even 4 G under braking and around 1 G acceleration.

Stopping uses 4 tire traction, accelerating only 2 tires - unless 4 WD
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Old 01-10-2013, 03:17 PM
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If you want to a Porsche engine on a dyno replicating track forces on the Nurburgring, watch this video, note the engine is almost turned upside down on its side at times. Imagine scavenging oil from the crankcase:

2009 Porsche 911 Engine Oil Sump Test Rig - YouTube
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Old 01-11-2013, 09:23 AM
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That's not my collection of pumps. I just stole the picture from the forum for my information gathering!


Also gotta keep an eye on that venturi screen add-on. Sometimes they break. Here's how I found mine a few years ago.

How often do you open up your sump plate?

Oil Sump Tube - How Much Of A Problem Is This?
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Last edited by KTL; 01-11-2013 at 09:31 AM..
Old 01-11-2013, 09:27 AM
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Kevin - so what did you find had lunched your motor in 2011?

I have a large collection of stolen pictures - they are great to have.
Old 01-11-2013, 10:45 PM
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Kevin, I'll second Walt's curiosity. I followed the link to your thread. The symptoms you experienced after removing the venturi plate/screen are EXACTLY why Porsche developed that fix in the first place. Without the plate to enhance flow through the scavenge pickup tube, your crankcase filled with oil during that 2nd hot lap. If you didn't kill any bearings when the oil pressure light went on, theoretically it should have recovered with no damage. Looks like the screen wires cracked at all the small weld spots. I doubt any pieces of the screen got loose and sucked up, and even if they did they went straight to the oil filter without passing GO.
DG
Old 01-12-2013, 05:02 AM
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Shamelessly stealing a picture and editing it to show the difference in potential crankcase oil level with the venturi pick up end versus an open pipe.

The upper arrow is where the pump will draw air without a venturi and lower arrow shows level with venturi.

The venturi not only helps the pump scavenge better to a lower potential level, but also to scavenge better when oil sloshes away from the pickup, thus it allows more oil to be pumped out of the crankcase while decreasing foaming as well.

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Last edited by Cupcar; 01-17-2013 at 08:45 AM..
Old 01-12-2013, 09:52 AM
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The oil screen issue was discovered before my 2011 engine problem. I didn't have a replacement screen handy for my next event (I was changing the oil a few days before the next race weekend) so I ran without it. Coincidentally I had a problem with the engine that weekend. However it was a chain tensioner idler arm binding on the post.

Upon disassembly the idlers were the old narrow style with no bronze bushings. The left (cyl 1-2-3) idler was stuck in an extended position and put a lot of tension on the chain, likely slowing the oil pump down really fast when the throttle was closed. Aside from that, I found nothing bad inside the engine. Well, with the exception of all 24 studs dililvar (std. coated smooth ones, not 993 full thread) and Carrera-style compression height pistons on my SC crank/rods...

Everything else looked pretty good inside. Just a lot of leaks (rocker shafts, head & cylinder & cam tower sealing surfaces) and tired bearings. Could have gotten away with nothing more than fresh bearings & seals and throw it back together. But I didn't like the mismatched pistons (deck height was ~2.4mm IIRC) so I decided to do some while-you're-in-there stuff and freshen things up for 2012.

I put in all new bearings (GT3 rod, std Glyco others), new new JE 10.5 pistons & rings, hardwelded cams, rebushed & refaced rockers, all new steel studs, twin plugged the heads w/new springs & retainers, replaced a few worn valves, cut the heads and seats, nice used 993 pump, 993 oil filter console, 245mm fan & housing, and i'm sure some other stuff i'm forgetting. Went all in to make it nice & fresh for 2012.

Ran pretty great at my first event with it. Actually won my first ever race in hellish heat conditions! The following event it took a dump first session on the track with some sort of oiling failure. Not 100% certain what it was. Engine Bearing Failure- Disassemble Heads Too? But what's done is done and i'm currently building it once again.

Sorry for the thread hijack. But it's all kinda oil related so i'm sure there's a benefit from all this oil pump & engine fail talk.
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Old 01-12-2013, 01:57 PM
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Oil Pump values

Since the pump supplies the pressure, perhaps this chart I found in my collection of stolen images has a place here:



Unfortunately, not all cells of the matrix are filled in, and not all those which are use the same units. But it is something.
Old 01-12-2013, 06:29 PM
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I have read the entire post, really impressive collaborations and I wanted to discuss my thoughts:

Doing the by pass modification has got one big problem in itself and it is that bypassed oil is not only oil but full of air bubbles, sparkling oil.

I don´t think it is a good idea to feed the oil pump with that mix of air and oil that comes out through the bypass oil valve.

And certainly don´t recommend it if you are not putting the big scavenge pump...I think it is totally balanced the why do it and why not do it.

Thanks for reading, hoping to read something back from this.
Fede.

Old 05-06-2013, 01:02 PM
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