Does an LSD need better cooling?

[Jeff Berk]

I'm getting back to installing an LSD in my R180 but I was concerned about the LSD heating up the differential during Auto-X. 

I drilled/tapped a hole in the fill plug for a temperature sensor but I also was looking into an alternate differential cover with extra volume and cooling fins. I located a family-run foundry operation that will do a one-off aluminum casting for $40 plus $3/pound so I designed one. 

Anyone want to comment on the design?

 

[Yarb]

Not an Engineer, Would multiple smaller fins dissipate more heat? Probably a question for @Captain Obvious.

[Captain Obvious]

I would expect one of the primary variables would be surface area. However, you should know... Thermo was my least enjoyed class of anything I ever had. Ever. And (like most people), I learn better when I like what I'm learning. 

@Jeff Berk, What casting method are they going to use? Are you going to supply them with a wax model so they can do an investment casting? Making a 3-D model that they will press into a sand casting? What??

Honestly, I can't get over the belief that someone is willing to do a one-off casting of that thing for $40!!!  Unless you are supplying the consumable model and assuming all the risk of whether it works or not, I'm completely floored by that cost!!

 

[Zed Head]

More fins is a good idea.  https://www.z1offroad.com/nismo/nismo/nismo-rear-differential-cover-upgrade-r200-p-2339.html

I wonder if they're using a 3D printing/additive manufacturing/stereolithography tool to create a wax form.  Lost wax casting.  Probably a lot easier to make the form with the new printers.  Zip it out, pack it, pour it, send it.

https://en.wikipedia.org/wiki/Lost-wax_casting#:~:text=Lost-wax casting – also called,cast from an original sculpture.

[Captain Obvious]

1 minute ago, Zed Head said:

  Lost wax casting. 

That's what I was asking. "Investment casting" is another name for lost wax.

[Zed Head]

The low cost of the 3D printers probably opens up a lot more opportunity for casting.  Used to be, I think, that you'd need a CNC machine to cut a form.  The upfront costs were very high.  

Hard to keep up.  I saw a guy make actual usable durable robust electrical parts with his printer.  The "work" was mostly calculating and using CAD to make the computer file.  Kind of disappointing, no handling of hard metal tools and setting up the machine to cut the piece.  Life just keeps getting physically easier.

Jeff Berk, does that family shop have a web site?  Would be interesting to browse.

 

[Patcon]

I agree, more fins. If you look at the factory R200 diff cover it has a number of thin fins

[Jeff Berk]

My worries about the fins was that I don't know how thin I can make them. They are 4mm across the top. I was warned that they need to be tapered to allow them to release from the mold. I have a spot on two of the fins where I can attach screws to mount an air deflector to direct air flow from below the differential across the back.

I don't know much about casting but my understanding is that the Cattail Foundary uses sand casting. They only do aluminum every few months so it might be a while for them to get to doing it. All they need is a 3d print that is scaled to account for shrinkage.

https://www.lancasterfarming.com/country-life/antiques-and-history/cattail-s-customers-come-from-near-and-far/article_bfdbf807-69b1-5194-9fee-762e003d46dc.html

Back to my original question, does the presence of an LSD heat up the differential more than an open differential? Should I increase gear lash slightly to account for the increase in temperature? I notice that my gear lash (pinion to ring gear) decreased when I installed the LSD so I had to do some shim adjustment.

 

[Patcon]

I would set lash based on the FSM for the 87 300zx turbo LSD. Yes, I suspect the CLSDs and VLSDs both create more heat. Clutch slippage is always going to increase heat. I can measure the factory LSD fins if you want some dimensions

[Patcon]

24 minutes ago, Jeff Berk said:

print that is scaled to account for shrinkage.

https://www.lancasterfarming.com/country-life/antiques-and-history/cattail-s-customers-come-from-near-and-far/article_bfdbf807-69b1-5194-9fee-762e003d46dc.html

Cool article! They sound busy!

How are you handling the shrinkage factor?

[Zed Head]

I wonder if $40 gets you the good aluminum.  The Z cover is a loaded structure, not just an oil holder-inner.  Not sure that old beer cans will do the job.  Better ask.

Diff cooling is a popular topic.  

These words in Google will find a bunch.  site:hybridz.org differential cooling

Here's a good one.

https://forums.hybridz.org/topic/133692-r200-differential-cooler-pump-and-plumbing/

[Jeff Berk]

1 hour ago, Patcon said:

Cool article! They sound busy!

How are you handling the shrinkage factor?

When I called in December they said they will be doing aluminum in 3-4 months so they are likely a very small, busy operation. I'm going to enlarge the entire structure using a percentage of around 6.5% to allow for shrinkage*. I guess if dimensions are critical, you don't use cast aluminum which is likely why you need shims when assembling a cast aluminum differential.

*Every time I see the word shrinkage I think of that Seinfeld episode.