901 Trans Cooling

[PFM]

All,

OK so finished the six getting ready to go back in the 914. I have the billet side cover and intermediate plate ready and plan to add a tilton pump and cooler. My question is what is the best place to locate a return line to cool the ring and pinion gear? Any other input to help keep the 901 alive behind a strong 3 liter please chime in.

[Dave at Pelican Parts]

Don't dump oil on them just as they start to mesh. I have read that this can cause problems with the actual mesh of the gear teeth. Better to hit them with oil just after they are in contact. That gives the best cooling, as that's where they should be the hottest. It also lets the oil sling off until just a film is left, which is what you want.

(NOTE: If anyone who works a lot on these transmissions contradicts me, listen to them. My information on this is second-hand.)

--DD

[John Rogers]

Sorry Dave but you have that one slightly misguided. The meshing of the gears will easily push out any unneeded oil. There are several articles here and on both the other 914 websites that cover the install of a trans cooler setup with many pictures. For street use it should not be needed and possibly not even for occasional auto-x duty. If you plan to road race or do running hard for 30 to 45 minutes you will surely need a cooling/lube system.

Most will have the suction in the bottom of the case and some (as I did) use the drain plug. The fluid is sucked to the pump through a micron type of cleanable fluid filter, then the gear type positive capacity pump then to the cooler and finally back to the transmission generally through 3 nozzles. They spray on the ring and pinion and two to spray on the top of the gear assembly. There has to be a COOL and constant air flow for the cooler and many run the air inlet from on top of the car or as I did from an inlet in the right side of the rear GT fender flare. If you run it from underneath you'll just get hot air. You will have to run a hard line from a vent adapter to a puke tank since you will now be running an extra quart of Swepco and if the car starts off with an open vent then there will be some fluid pumped out. The final item is a transmission temp gauge that uses a plug replaces the transmission speedo plug and uses a calibrated (to it) VDO gauge.

Two ways to do it, buy a complete setup from Jim Patrick in Phoenix (as I did) to save time or work at piecing all the needed parts to make your own which in the end is just about as expensive. In either case, only use Earl's braided flex lines and make sure to get plenty of cool air to the cooler.

[TheCabinetmaker]

Yes agree cool source of air is the trick. very few locations on a 914 to get this without external body modifications

[PFM]

John,

I have the parts the question is where to place the 3 return lines? I searched around the two 914 sites but did not find what I am looking for. In a perfect world I would like to point it at the pinion but getting a good angle is not so easy.

Can you point me at a link?

Thanks,

[John Rogers]

When I modified my cases (K-Q-V and M-S-X) I drilled and taped a hole right over the ring gear, slightly off to one side. The other two returns went on top of the gear set. There is not a lot of room between the top of the transmission and trunk sheet metal and to get a bit more I had lowered the engine and transmission about 3/4 inch. I made the tee connections inside the rear trunk and drilled holes for the lines to go into the transmission.

One huge benefit of this cooling and lube system is to empty the transmission all you need to do is break the cooler outlet and run a hose to a large container. Remember there are now 4 quarts of fluid and not three so I used a huge clear plastic ex-pretzel container to hold the fluid when pulling the engine and trans.

[PFM]

John,

So you dodged the input shaft by going off center. I was looking for a side shot below the input and right at the union of ring and pinion. The main stack gears are odd the lower gears are in a bath, the uppers need help. The intermediate plate bearings could use some help too.

Still open to input, pictures would be great!

[Jon B]

Originally Posted by Dave at Pelican Parts

Better to hit them with oil just after they are in contact. That gives the best cooling, as that's where they should be the hottest.(NOTE: If anyone who works a lot on these transmissions contradicts me, listen to them. My information on this is second-hand.)

Dave, you are correct, modern motorsports transmissions spray gears out of mesh, not into, for the reason you mention. This wasn't always done by Porsche or others, their racing transmissions sprayed into mesh for many years. People still do this in club racing, it's fine but not optimal.

I used to build Indycar transmissions at Swift in the 1990's. Gears were spayed out of mesh, while bearings and differential were pressure-fed. Transmissions were dry sump with 2-stage internal pump.

[chris_seven]

I spent many years making high speed rotating equipment test rigs and high speed gearboxes - up to 82000rpm.

If you let lubricate gears on the 'input side' the oil will virtually explode and you will have a box that will breathe an oil mist and the windage loss will increase dramatically.

It is far better to inject oil into the trail side of the gear and with this arrangement it will be much more stable.

It may not matter so much at lower speeds and at 5-8000 rpm spray lubricated gears are rare (at least in industrial boxes)

Oil lube bearings are a completely different issue and both the quantity of oil and the angles at which they are lubricated are critical.

We used to routinely run 50mm dia angular contact bearings at 50 000rpm with oil jet lubrication and they could be made to last for many years.

It is very unlikely that the bearing in a 901 transmission need much help in terms of lubrication but oil flow may help cooling.

The temperature of the bearing will be the key and I think you need to measure the bulk oil temperature.

I would think that the bearings used will run at up to 80degC.

We used to routinely monitor gearbox bearing temperatures and used a strategy that set of an alarm at 80degC and a trip at 100degC when we would shut down the rig.

We also used to pre-heat systems to 50degC before running test rig gearboxes at full load.

We used the same strategy for all boxes whether they used spur gears, helical gears or spiral bevels.

I would also think that the biggest issue with temperature would be the growth and reduction in clearances that could result and keeping the 'bulk' temperature of the box under control is probably the most important issue to maintain correct backlash etc.

[PFM]

All,

Thanks for the valuable input. The into mesh or out is very interesting as is the loss of clearance due to increased temps. The 901 box has some quirks with stock input power levels they do OK, add an LSD, as I have, they get warm. As you add TQ to the motor heat goes up the load at the R&P gets crazy and tries to push the side cover off and dries to push the intermediate plate out the back of the car. The load on the bearing that resists the pressure from the pinion gear thrust must get really crazy. All this was mostly under control at 200 FT/LB motor TQ. So now looking at close to 250 FT/LB of TQ it looks like more is required.

Spraying the R&P gears going into mesh seems like the correct location to ensure the contact area has cool lube just prior to max load. Is my thinking wrong? If the oil jets are just to cool out of mesh makes sense to me. The R&P is the first fail point I see on the 901 when motor TQ and large sticky tires are added. The intermediate plate bearings are the second fail point, if the race spins it will fail.

Chris, on you test rigs did you have bearings loaded in the same manor as the 901 intermediate plate gears? Is a jet spray viable? I would love to pressure lube it but hesitant to drill holes in the plate for that idea.

Keep the thoughts coming. Jon I would love to hear more on the race boxes too.

[PFM]

Chris,

Failed to mention with the 200 FT/LB motor on track oil temps hit 250F, ran synthetic lube at the time. The LSD greatly adds to oil temps. That trans had no cooler but clearly needed one. The gears looked great, bearings went about 2 seasons.

[John Rogers]

Since you are in the southern CA area, there are two people you could call and talk to or even visit. First is Wayne Baker and he is the driver of the famous #22 914-4 yellow car and runs a well respected race shop in San Diego. Second is Jim Patrick over in Phoenix and he is about as same knowledge as Wayne but a bit younger. See what they say on how to return the oil to the case and such.

The engineers that talk about the location of the oil spray seem to not take into account the gear profiles in a 901 transmission, the meshing pattern we have and the closeness the gears are to the inner case walls. Finally we have to deal with a fairly weak case without a lot of areas we can actually drill and tap for the returns.

The temps on my 901 boxes would get over 275 or so and slowly the shifting would get harder and the only time that happened was on short straights street races in Tijuana or Tecate MX. There was never enough time to fully cool the trans well before shifting again. So I added a mister system that was a switched sprayer from JC Whitney as an add on windshield washer system. It sprayed into the air feed to the cooler and would drop the temp by at least 20 degrees. Shifting got easier and things were better.

[PFM]

John,

I ran this past a friend that is employed as a drive line engineer, his feedback was this. If you are cooling parts spray them out of mesh, if you are adding oil due to load issues (I am), spray at point of contact. You are adding oil where it will be put to use. That makes some sense to my head.

[Jon B]

Originally Posted by PFM

I was looking for a side shot below the input and right at the union of ring and pinion.

This would be "out of mesh". Oil sprayed above the pinion in a 914 transmission is after mesh; above the pinion in a 911 transmission is before, or "into mesh". Ring gears of the two models rotate in opposite directions...

[PFM]

Jon,

Yikes you are right! I just did a visual and yes into mesh is below the pinion. Any input on how to point a jet at the right spot? Now I need to go out and look at the case or I will not sleep right tonight. In theory the ring gear should be coming up out of an oil bath just before mesh.

Thanks for the input.

[Jon B]

Originally Posted by john rogers

The engineers that talk about the location of the oil spray seem to not take into account the gear profiles in a 901 transmission, the meshing pattern we have and the closeness the gears are to the inner case walls.

John,
Please explain gear profiles and meshing patterns of a 901 transmission, and how these would have an effect on oil spray location.

[John Rogers]

When I installed the cooling and lube system in my transmissions, I followed what the winners in HSR and VARA had been doing for a while. Remember this is a COOLING system first as the transmission gets most all the lube it needs from splashing. The additional quart of lube helps with the heat absorbing greatly.

The reduction gears on the CVN65 had the oil sprayed into the mesh and every 5 years we had an inspection where we would have to observe the spray pattern while jacking the engine over. The excess oil ran out the sides of the gear mesh. Of course they were double helical cut gears for thrust elimination and noise reduction and long life.

http://www.navsea.navy.mil/nswc/carderock/src/mechrel/products/handbook/CHAPTER8RevA.pdf

[Flieger]

I like what Chris and Werkstatt have to say. Very informative.

[Jon B]

Originally Posted by PFM

Any input on how to point a jet at the right spot?

Photo below of spray nozzles from transmissions currently in the shop, a Porsche 911 RSR and a Porsche 908. Each has two exits at tip, for the pinion and ring gear. The longer 908 nozzle is fed from a flexible line outside the case.

I'm curious to see how current cooling kits are directing oil to the ring & pinion.

[PFM]

Jon,

Now this is progress! Thank you for the pictures. If possible could you provide photos of the transmission and how these are possioned? The two shown are from two different transmissions? As drilling into the case can only weaken it I would really like to get this right on the first try.

Again much thanks,