Jeff Curtis

Truth be told, I've considered the whole gear-mesh -vs.- 75W/90 lube being "dumped" in there issue...it's potential damage from overkill that concerns me.

Heck, there are guys in the Sports Racer and Formula (SCCA level) car world using Dexron ATF in their manual gearboxes to get more power out and efficiency through the drivetrain, but at a price...a price that goes towards frequent gearbox rebuilds...that's the opposite end of the spectrum that we're discussing though.

Jason, was the basic gist of the paper that suggested 6% efficiency per X degrees was in reference to the cooler a gearbox ran, the more inefficient it was or how efficiency went up with reasonable heat?? ...in other words, was it suggesting that if you cooled it down too much that it would cause resistance and at that point be a power leach?

I can't tell from your post at which end of the issue they were concerned with.

Great discussion by the way...I still have to figure out what size lines/hoses/fittings I have as I thought they were -10, but the outlets measure 1/2", which is -8...although some numbering on the fittings have a -10 in them...I want to use -8 and want to figure out the optimum area to discharge the cool side of the pump to. I think picking up at the drain plus is the ultimate plan.

Geoffrey, others...did you use some type of nozzle/aperature at the discharge end to slow or spray the return of cooled gearlube or just a wide-open -8 fitting dumping the lube back in? I would think some type of resistance might be necessary - sure, that would increase pressure at the discharge, which could heat up the lube a couple degrees, but I feel that would be a negligible result in this scenario - NO??

Geoffrey

Wide open discharge. My concern was temperature only, not lubrication per se. Like I said, for what we are doing I think the KISS principle works well.

Jeff Curtis

I agree Geoffrey, totally agree, just trying to avoid a "faux pas" which could be easy to do something "wrong" in this biz, if you know what I mean. I may put this idea on the back-burner as time is a constraint this week and I'm due at CMP next weekend...may drill and weld a bung for the proposed fitting, put the fitting in and block it off?

All the other work can be done with everything in the car, I think.

BC

How did this work out for you Jeff?

BrianKeithSmith

After this weekend at VIR - I'm going to need to add a cooler to my 930 box.

Question : can I (for now) re-deposit the cooled oil via normal fill plug that is on the side of the 930 box? Or is that an issue?

Next time I pull it all down and have everthing apart I'd probably place a port on the top of the tranny similar to what Geoffrey did, but for now, can the fluid simply re-enter via the fill plug on the side?

And one other question, assuming the answer to the above question is Yes, as you guys are adding these coolers and plumbing, pumps, etc, I assume you guys are increasing the volume of gear oil you are adding to the tranny?

Thanks,

Brian

kurt M

Good thread. 2 questions. How much do the pumps run?
Has anyone ever used the existing power steering pump on a 993 motor as a trans cooler pump?

Geoffrey

1) Yes you can, however, you'll have to figure out how to determine the trans is at the appropriate level for oil. Adding the cooler, lines, and pump will increase your fluid requirements. My setup requires 1 more litre than factory, so I run 5 litres.

2) For the Mid Ohio enduro race which started at about 70 degrees ambient temp, my gearbox was 32C. After 18 laps including the warmup lap, my gearbox was at 90c where my pump comes on. It cycled on and off the rest of the race which lasted 51 laps total. I'll have to log the aux output to determine how long the pump was on vs off. If I remember, I'll do that for WGI this weekend.

Tom W

Some additional data for what it's worth ... My temps hit 229 F after 26 minutes of a race at Sears Point earlier this year. The MoTeC data says the inlet air temp to the engine was 96 F - I think the nominal air temp was about 88 F. With my dual oil coolers, the engine oil stayed at about 210 F, but the gearbox temps kept climbing.

I'm running a brand new G50/32 so I will probably have a transmission cooler put in soon to protect my investment.

JackOlsen

Before I had a transaxle cooler, I frequently saw higher trans temps than engine temps at the track.

As I understand it, transmission oil breaks down at lower temperatures than engine oil.

This is a 915 with Swepco (dyno) oil in it, though.

BrianKeithSmith

So now the question is (and its not so obvious to me) - if for the short term I use the fill plug as the re-entry point, how do I get MORE fluid in there than the standard 4qts or so????

Would that even be possible with that type of setup?

Brian

Geoffrey

In my case, I have quick disconnects, so I disconnect the trans output and put an adapter with a hose on the line going to the pump. Then I turn the pump on and suck the fluid out of the gear oil bottle. When full, I simply reconnect the trans output.

So, at a minimum you could do that to fill the pump, the cooler, and the lines. Then you could fill the trans normally and you should be right where you need to be.

BrianKeithSmith

Gotcha. I figured you were "priming" the system in some way in order to get everthing filled.
Thanks,

Brian

JoeMag

Kurt -- I haven't heard of anyone using the PS pump on motor but then I'm not a wealth of trans cooling knowledge either ...actually not sure it would pump that glue of trans oil or if it could self prime itself. the trans pumps actually tell to not run them until the oil is warmed up and they're self priming.

Brian -- are you using the drain hole as suction location?

BrianKeithSmith

I'm not using anything currently, but am considering using the drain plug as the suction point.

Jeff Curtis

Brian, you might consider putting a cooler setup on your TAILPIPE!! ...that NASA sticker on your bumper is looking a bit "toasty" here lately.

Maybe Geoffrey (white/blue 964 racer) will chip in here as the thread has officially been 'revived' - I have a complete cooler setup but need to further discuss with him how he setup that bomb-*** suction/discharge setup with the banjo fitting in the drain plug fitting.

I do know that you don't want the pump to operate until the gear lube in the transmission is at a decent temperature and I have talked with local shops who set these up on their 996 Koni Challenge cars and ensure they are not dumping the cooled lube at a high volume in between any gearsets as this could cause stress issues.

I'm all for just using the drain plug area as a suction then maybe reducing the out flow as to slow down the process of exchanging the fluid and dumping it right back into the differential cavity...I think Geoffrey has his setup.

I want to explore the idea of slowing down the discharge end so fluid can move into the differential cavity from the mid-section and so on so it gets sucked up and moved through the cooling system - make sense?

Geoffrey, can you put together a few banjo fittings for our drain plugs for us? ...I know I discussed this with you about a year ago and then got caught up on other things and just wound up putting my damn gearbox back in - it works GREAT until it gets hot then it doesn't want to downshift too smoothly and gives me a little "static" when up shifting from 3rd to 4th.

I have come to the conclusion that when you use a lightweight flywheel, things tend to slow down too much between shifts and when the gearlube is nice and hot things don't like to mesh too well at shift/downshift speeds as it's the only explanation of why things work beautifully when the gearbox is at a decent temp. and why things get "baulky" at higher temps.