2018 GT PP2 Rear Differential Overheating Issue

[shogun32]

since someone mentioned Mishimoto... Regarding the Full-Tilt Boogie or similar kit I wonder why you wouldn't want to mount that to the inside of the spare tire well. Sure, I'm not up on my weather sealing grommets but there would be much cooler air in the trunk (how air-tight is it? or open to rest of cabin) and it would protect the various components.

Definitely any kind of 'drip' system would get you banned for 'oiling' the track.

I'm trying to think of a water-block or water-jacket that could be attached to the back of the diff housing and run a PC or fish-tank water-cooling rig like setup. Ok, this is deep into the 'ghetto-engineering' end of the spectrum. Cast-iron is a lousy conductor of heat so anything that doesn't cool the oil directly is probably a completely waste of effort. But a water jacket could be removed very simply and be low pressure and if it failed or stopped circulating, no big deal. Hmm, how about using the radiator and pump but put the radiator in a bath of ice water? You could mount the tank like you would a fuel cell. Toss in a bag of ice every session or two.

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[sigintel]

since someone mentioned Mishimoto... Regarding the Full-Tilt Boogie or similar kit I wonder why you wouldn't want to mount that to the inside of the spare tire well. Sure, I'm not up on my weather sealing grommets but there would be much cooler air in the trunk (how air-tight is it? or open to rest of cabin) and it would protect the various components.

Definitely any kind of 'drip' system would get you banned for 'oiling' the track.

I'm trying to think of a water-block or water-jacket that could be attached to the back of the diff housing and run a PC or fish-tank water-cooling rig like setup. Ok, this is deep into the 'ghetto-engineering' end of the spectrum. Cast-iron is a lousy conductor of heat so anything that doesn't cool the oil directly is probably a completely waste of effort. But a water jacket could be removed very simply and be low pressure and if it failed or stopped circulating, no big deal. Hmm, how about using the radiator and pump but put the radiator in a bath of ice water? You could mount the tank like you would a fuel cell. Toss in a bag of ice every session or two.

Geto is good.
Keeping it simple is good.
I was considering running a spare washer fluid line to spray the diff. As long as it flashes to steam and doesn’t douse the track it might be enough.

 

[Hack]

Geto is good.
Keeping it simple is good.
I was considering running a spare washer fluid line to spray the diff. As long as it flashes to steam and doesn’t douse the track it might be enough.

I would highly advise you not to do that. It's just too risky in my opinion. I would be really irritated if you doused the track with water right in front of my car.

 

[aleccolin]

Geto is good.
Keeping it simple is good.
I was considering running a spare washer fluid line to spray the diff. As long as it flashes to steam and doesn’t douse the track it might be enough.

I don't know of any racing or track day clubs that would let you run an intercooler mister and some won't even let you run water/meth injection. If you're lucky they'll let you run an empty reservoir, but usually they'll make you remove it to pass tech. I would say your diff mister idea is unlikely to be allowed.

 

[sigintel]

Uhhh.... if you race wheel to wheel in WRL, Champ, Lemons, enduro series... there is tons of shit on the track way worse than water.
Typical HPDE track days w Chin, Edge, etc its not uncommon for someone to have overfilled coolant and see drip runs on trackout heading to paddock end of session.
Some people run their AC. Lol.
Drivers edge, Chin, etc aint checking out the underside of cars every run group.
A spray pattern hitting top front of 220F diff is not going to wet the track at 80 mph. Now if you stop on track and start hosing for 60 seconds, then maybe, but that goes for hitting your windshield wipers too. Dont do stupid shit.

Aleccolin wtf are you talking about? Someone made you remove an IC mister or meth setup at an amateur track day? They made you empty your washer fluid? I have never heard of anyone giving a shit about either of those in 200+ track days since late 90s.
We once made a novice run all the way to track control with his helmet on to get a new muffler bearing for passing under yellow, but forcing someone to empty meth, mister, or washer fluid is uhhh silly.

I dont think diff water spray is a good permanent solution since it would suck constantly topping off, but it would be useful to establish temp drop given a know flow rate of water.
I have no doubts that it would be impossible to create a slick spot on track at 80-140 mph. Thats just silly.

 

[aleccolin]

Aleccolin wtf are you talking about? Someone made you remove an IC mister or meth setup at an amateur track day? They made you empty your washer fluid?

Yes, at an SCCA time trial event. OE equipment like washer bottles and coolant reservoirs were allowed. Maybe it’s track specific.

 

[Grintch]

A time trial is not a track day. Times trials are competitions, with classes, and rules. Track days are not.

 

[JohnD]

A time trial is not a track day. Times trials are competitions, with classes, and rules. Track days are not.

Every track day I've ever done has rules and classes though they've all stressed "IT'S NOT RACING!!!!".
How well they enforce the rules is a variable thing though.
But they've all got rules, and classes.

 

[shogun32]

Considering the original part (GR3Z-4033-A) is only $65 I can buy a couple and experiment with machining. After thinking on it a while I think a simple, bolt-on passive radiator would be both very inexpensive (less than $100) and sufficiently effective. As I mentioned before cast iron is a horrible, horrible conductor of heat. The 'perfect' solution would be to cast a copy of the cover in aluminum but I don't have the engineering resources to do that, (hmm or do I...)

Drill and tap 2 holes like the Full-Tilt Boogie guys do and screw in a AL or Cu posts. Bolt on a finned block of Al or Cu at least externally but internally too if clearance permits. No fluid leaves the unit. All heat migrates thru the threaded posts. No, it won't remotely match the carrying capacity of the FTB or Shelby setup but it basically can't leak, doesn't require electricity, sensors, pumps or hoses.

 

[Hack]

A time trial is not a track day. Times trials are competitions, with classes, and rules. Track days are not.

Right - time trials are actual races versus HPDEs which aren't timed. An HPDE definitely won't void your warranty. I'm not so sure about a time trial. Seems like it might.

 

[ihasnostang]

Ok, 75w140 and wraps installed, albeit sloppily. I shall see how it holds up next weekend in 100 degree temps. Also, does anyone know what this is? The thing im pointing to in the pic right behind the diff. Its like a flexible rubber... somthing. I thought the bolt was backing out at first.

you know i would be curious what the surface temp of that driveshaft is when the diff starts to get too hot. i dont think there would be much heat added to the system simply by the DS rotating. i looks like there is some sort of heat shield but basically the whole lenght of the driveshaft is packed in tight by the exhausts.

 

[shogun32]

I ordered a brand new back-plate (cover) for the diff housing. It is a lovely piece of cast aluminum - NOT cast iron. The walls are about 3/16" thick. So from a heat-sink standpoint should be really quite decent. Is there really that much mechanical friction being generated by the diff gears? Need to dig up my IR thermometer.

I also bought 30' of heatwrap/blanket to keep the exhaust from irradiating it. I might take an 1/8" endmill and cut a pattern of channels in the inside surface. Maybe I should "pull a Ducati" (see current hoopla over 'cooling' vane in MotoGP) and use some ducting to force air into close-contact instead of relying on 'eddy' flows.

The $1000 oil cooler is obviously tough to beat from an efficacy standpoint.

 

[Norm Peterson]

I ordered a brand new back-plate (cover) for the diff housing. It is a lovely piece of cast aluminum - NOT cast iron. The walls are about 3/16" thick. So from a heat-sink standpoint should be really quite decent. Is there really that much mechanical friction being generated by the diff gears? Need to dig up my IR thermometer.

The thermal property that you're really looking for (for sustained thermal loading) is heat conductance. Heat sink properties only gets heat out of the fluid for as long as the "heat sink" is cooler than the hot stuff you're trying to suck some heat out of.

If you're putting 300 hp to the wheels and the differential is 98% efficient (which is probably an unrealistically high value), that means you're turning 6 hp mostly into heat. Or around 4500 watts . . . about like two 8" stove top elements going full blast. And that's a low estimate.


Norm

 

[Hack]

If you're putting 300 hp to the wheels and the differential is 98% efficient (which is probably an unrealistically high value), that means you're turning 6 hp mostly into heat. Or around 4500 watts . . . about like two 8" stove top elements going full blast. And that's a low estimate.

Norm

That's a good example, but remember that the 300 hp comes and goes. You are only applying the 300 hp when the gas pedal is to the floor. Not during braking or cornering/maintenance throttle situations.

 

[Norm Peterson]

That's a good example, but remember that the 300 hp comes and goes. You are only applying the 300 hp when the gas pedal is to the floor. Not during braking or cornering/maintenance throttle situations.

That would take a full-blown thermal transient analysis, carried out with a power/heat input time history and a s-ton of other variables.

Keep in mind that 2% and 4500W are low estimates; reality is closer to double that (like the whole stove top glowing at full brightness). We know that the heat from one cycle at full power doesn't all dissipate before we're into the next full power cycle, hence the fluid temperature increase until the warning gets triggered and the driver pits in.

These examples are really only for illustration purposes, in terms that can perhaps be visualized in terms of "how much" rather than "yeah, the diff gets hot". That for much of the time you're out on the track there's a fairly serious amount of heat being generated back there.


Norm

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