How much oil to run in an inverted Porsche 930?

[Jac Mac]

In the photo above, which shaft of gears has the gears firmly locked in place, and which one allows the gears to rotate on bushings (assuming typical transmission construction)? If the lower shaft is the fixed or solid piece (with gears cut into a solid shaft), would the importance of it now being submerged in oil be as important as the upper shaft gears floating on bushings, which is now in the "dry"? On the T-5 trannys that I've built, this was the case with the counter gear in the oil, and the mainshaft (with floating gears) that drove the output shaft was in the "dry".

Both shafts have gears spinning on them, 1st/2nd on the top shaft of above pic to RH & 3rd/4th on lower to left, attached pic & dwg might help you get your heads around the issue. This is more critical than aiming squirters @ the gear teeth & getting oil onto those rollers/bushes or even steel to steel in some types.

 

[Terry Oxandale]

Here is my interpretation thus far:

The photo on the left is the inverted, and on the right, normal side up. The red arrows point to a volume of oil within the ring gear casing (the round portion) for the same side inverted or not. The orange arrow shows the opposite side volume of oil in the ring gear casing. The point of these two arrows is to point out that the amount of oil in this portion cannot be the same inverted because the remainder of the housing (encasing the shafts and gears) is lower, and hence, should hold a larger percentage of the total amount of oil in the box. In other words, in the normal orientation (right side photo), the oil level should be slightly lower as compared to the output shaft seal.

The black lines are my rendition of where the oil level is with Ron's 4 quart measurement in the previous posted photos. I question how this will relate to the level of a normally oriented case (right side photo) due to the higher percentage of oil to be held in the ring gear case (more bulbous before it levels out into the shaft case - orange arrows) as compared to the inverted case. In other words, the oil should start flowing into the shaft casing at a lower level than with the trans is inverted. I've looked at my case and dimensional drawings, and can only assume the above is true. What exists inside the casing may negate my thinking on this.

The most important thing I want to illustrate is the transparent white arrows. These show the estimated oil level shown once again with the black lines. Notice that in the normal orientation, the oil would appear to be below (or barely touching) the lower shaft gears, whereas, in the inverted position, the lower shaft is now immersed in oil. Also note that the input shaft seal is now completely immersed in the oil whereas the original orientation it is in the dry.

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The curved black-line arrows show oil throw direction based on ring gear spin. In the normal position it throws oil into a moderate sized hole (green arrows) onto the upper shaft gears. In the inverted position, it throws oil away from a much smaller hole (based on Russ' description on an earlier post), most likely reducing this attribute.

The round transparent white circles are an estimation of the location of the missing output shaft bearing, only used as a reference in Ron's oil level description.

 

[Bill Musarra]

Ron,
I think Russ's setup is good for getting the oil to the R&P. Can't tell if he is getting the gears as well or usinjg the splash. When I got mine done by my shop foreman buddy, I knew there was little info on how much lube to use. That is one of the reasons I chose the spray bar apparatus. Once that was made I decided to go with direct spraying of the gears and the R&P. That way if I mis guessed the volume to use, I would know the gears were getting plenty of oil. I chose to oil only 2nd, 3rd, and4th along with the R&P as 1st is all but useless unless I go for a different gear set down the road.. Here are the spray heads for the gears.

And here is the R&P and spray bar manifold.

I used an Aluminum manifold I found on Aircraft Spruce.

ALUMINUM MANIFOLD FITTINGS from Aircraft Spruce
I believe I got the 528 manifold, then used a 45 degree 1/2 npt to 10 adapter for the AN10 lines from the cooler and used 1/4 npt to AN4 lines for the sprayers.

Bill

 

[Russ Noble]

Terry,

If the circular arrow is the direction of rotation of the ring gear, then you've got it wrong in the inverted GT40 position. Not sure how that translates into the mirror image photo though. I think its wrong in both of them in respect of the way the oil from the oilbath is being thrown into the pinion. GT40 is straight in, about 90° ring gear rotation, Porsche approx 270°

 

[Ron Earp]

The black lines are my rendition of where the oil level is with Ron's 4 quart measurement in the previous posted photos. I question the level as compared to a normally oriented case due to the higher percentage of oil to be held in the ring gear case (more bulbous before it levels out into the shaft case - orange arrows) as compared to the inverted case.

The most important thing I want to illustrate is the the transparent white arrows. These show the estimated oil level shown once again with the black lines. Notice that in the normal orientation, the oil would appear to be below (or barely touching) the lower shaft gears, whereas, in the inverted position, the lower shaft is now immersed in oil.

The curved black-line arrows show oil throw direction based on ring gear spin. In the normal postion it throws oil into a moderate sized hole onto the upper shaft gears. In the inverted position, it throws oil onto a much smaller hole, most likely reducing it attribute.

Terry, I'm pretty sure that the oil was evenly distributed in my case as I measured it since I rotated the engine with the starter with it in gear for about 20 seconds between each quart and then let it drain down for 5 mins before drawing the line.

Surprisingly, when the engine was turning everything over the level remained stable within a couple of millimeters.

Bill, my oil return all comes into that lower port on your picture. You've got three shown, basically a triangle, mine returns in that position. What gear is that? I'll look at the case, it might be easy for me to tap more holes and split the returns off.

 

[Terry Oxandale]

Terry,

If the circular arrow is the direction of rotation of the ring gear, then you've got it wrong in the inverted GT40 position. Not sure how that translates into the mirror image photo though. I think its wrong in both of them in respect of the way the oil from the oilbath is being thrown into the pinion. GT40 is straight in, about 90° ring gear rotation, Porsche approx 270°

Thanks for the correction Russ. I've changed it, but this means no "spray" from the RG. Fortunately, you've noted a different benefit.

 

[Ron Earp]

Both shafts have gears spinning on them, 1st/2nd on the top shaft of above pic to RH & 3rd/4th on lower to left, attached pic & dwg might help you get your heads around the issue. This is more critical than aiming squirters @ the gear teeth & getting oil onto those rollers/bushes or even steel to steel in some types.

So, what do you think Jac Mac? No benefit in putting in more than the four quarts that we've got now? Unfortunately, I have no oil squirters in my transaxle.

 

[Jack]

No squirters in mine either. I guess we'll go with 4 quarts as a starting point. Should be enough splash to lube okay. I keep coming back to the 4 quarts.

 

[Ian K]

For accuracy, James Patrick said "The gearbox uses 3.4 quarts + oil cooler system", so I assume 3.4 quarts is transaxle and filter ...

Using Molleur's numbers for cooler, pump, and lines, that would put it at approximately 4.4 quarts total. I wonder how much higher up the level would be with the extra .4 quarts.

Ian

 

[Jack]

Ian,
I believe the 3.4 quarts (I have seen 3.7 quarts too) is for upright gearbox, not inverted.

 

[Jac Mac]

So, what do you think Jac Mac? No benefit in putting in more than the four quarts that we've got now? Unfortunately, I have no oil squirters in my transaxle.

I dont have any practical hands on experience with running Porsche box's, but I would approach this same way as I do everything else & try to visualise whats happening inside the trans. Your case is a bit unique in that you want this thing to last for 13 hrs virtually non-stop?... I think I would feel better if it had a squirter setup for all gears & the R&P, plus the LSD if it has one in an event like this.

Attached dwg gives a few indications as to what happens to the oil level under braking/acceleration, plus if the track involved has any high 'G' sweepers dont forget to allow for all the lube being stacked up to one side of the case for a few seconds. The 'Down' side of any squirter/dry sump type arrangement that it itself has to be very bulletproof to live for that length of time in regard to vibration, filters, screens etc. A horizontal lengthwise tube in the bulkhead of the trans case between R&P and G/Box sections at about static oil level height so that oil tended to stay in each section under braking/acceleration would be a small advantage. That tube would need to extend into both sections by about three inches to be effective.

XTRA-In Terrys post #42 above the oil level in the inverted trans ( LH pic ) could be set at just on the bottom side of the input shaft to equal the porsche level depicted in the RH pic, Im guessing that would be somewhere in the three to four quart range going by the pics you have posted.

 

[Terry Oxandale]

Going against intuition, but looking at oil levels, it would appear the inverted box is a win/win situation in regards to oiling coverage. In the OEM orientatiion, only a small portion of the gears are immersed in the oil (static situation) and the RG must carry oil further through its rotation to lube the pinion.

In the inverted orientation, the gears (other shaft) appear to be fully immersed and the RG rotates much less before oil is transfered to the pinion.

From strictly an oiling perspective (not cooling), it would seem one could actually reduce the amount of oil in the inverted case as compared to the OEM orientation and still have adequate exposure to the gears (obviously not an easy thing to contemplate).

 

[Russ Noble]

Terry, I think you've analysed the situation rather well.

This is the same conclusion I came to when determining levels to run in my trans. As you say the big caveat is the cooling, not the lubrication. If you've got a cooler I'm sure that oil level is fine. My dynamic oil level is at about the bottom of the input shaft shroud, static about 20 mm higher. No idea what that equates to in volume Ron, but I'll check it before it goes back in, in a few weeks. It's not out yet. LOL.

Admittedly I am returning via a spray bar onto all gears and the pinion but I think this is totally un-necessary. I just figured since it had to be returned to the trans somehow, I might as well do it through a spraybar. Not a lot of extra work and ensures lubrication under surge conditions etc as alluded to by Jac Mac.

Although I think what a lot of people are forgetting, is that the inside of the trans is all the time going to be showered by copious quantities of oil that is being spread around by the gears and ricochetted and draining everywhere inside. And I don't think surge will affect this much. Note the problems the odd person has had with oil being thrown out the breather. Besides being possibly caused by poor placement of the breather, this could also be an indicator that oil levels are too high?

 

[Ron Earp]

this could also be an indicator that oil levels are too high?

Absolutely, which is why I started the thread in the first place.

It is doubtful that we'll be fitting this transaxle with a spray bar. I'd like to but there are many things to do and not so much time.

I think I'm going to leave mine right at four. The cooler holds maybe 1/3 a qt so that should drop the level a tiny bit but still have the lower shaft completely immersed in oil.

 

[Jack]

Same conclusion I have come to Ron..

 

[Ron Earp]

A horizontal lengthwise tube in the bulkhead of the trans case between R&P and G/Box sections at about static oil level height so that oil tended to stay in each section under braking/acceleration would be a small advantage. That tube would need to extend into both sections by about three inches to be effective.

XTRA-In Terrys post #42 above the oil level in the inverted trans ( LH pic ) could be set at just on the bottom side of the input shaft to equal the porsche level depicted in the RH pic, Im guessing that would be somewhere in the three to four quart range going by the pics you have posted.

Thanks for the info Jac Mac.

Surge, yes, could be bad. We accelerate longer than we brake, but we brake at a high G loading, while acceleration not so much. On acceleration I don't think we'd be in danger since the R&P housing is lower than the gear box area and thus some oil will always stay in the R&P housing. But on braking it seems we could pile up a lot of oil in the R&P area of the box.

How big is the channel in this box for moving oil around, about 1 inch square Russ mentioned? Seems a lot of 90W could go through a 1" hole in short order.

 

[Terry Oxandale]

And here is the R&P and spray bar manifold.

Bill

Bill, can you describe the adapter that connects all of this to the aluminum case. At first I thought you'd use something like a -10 ORB fitting, but looking more closely, I see no hex nut, and no welding, so can you elaborate on this please?

 

[Russ Noble]

Here we go, photos and oil levels/volumes in an inverted 930.

In the first pic,the oil level to the bottom of the bung (lower black line) is 2¼ litres. You can see that is approximately in line with the bottom of the input shaft. This also coincides with the level at which the teeth at the bottom of the crown wheel are fully immersed. IMO this is as high or probably higher than the oil level requires to be. Dimi in another thread has established roughly (G50) that the dynamic oil level drops by about a litre when the trans is working.

So second pic shows the static oil level with an extra litre of oil added. ie 3¼ litres total. This is approx in line with the bottom of the driveshaft flange. This is the static level at which I have been running my oil.

Pic three is just a reference pic of the trans with the gearsets fitted. In this case my close ratios. And for Ox's benefit also shows my simple spray bar.

So Ron, I hope that gives you something solid to make your decisions from.

 

[Ron Earp]

Here we go, photos and oil levels/volumes in an inverted 930.
So Ron, I hope that gives you something solid to make your decisions from.

Much appreciated! But, I did the exact same experiment on my own tranny last month and posted photos too, only I can't remember where I posted them. I came to the same conclusion that you did though.

Did you guys break something to make you take it out of the car and tear it down?

 

[Dalton Veitch]

This has been a fascinating discussion on the seemingly simple subject of putting some oil in a gearbox. Lots of thinking, experience, and ideas. Thanks for looking at it seriously, Ron.