Rear Diff Cover

[Bahndvr]

Someone had a rear finned diff cover made?

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[JohnVallo]

Someone had a rear finned diff cover made?

Here is a better picture of the finished product

REF: https://www.mustang6g.com/forums/th...overheating-issue.106844/page-19#post-2992961

 

[AlbertD]

Well that is interesting... Curious to hear more data on it.

 

[FluiX]

Hello all. I am the designer of this diff cover. I am glad that it is receiving some positive attention. Since I am not a Forum Vendor and I do not want to violate any forum rules I will say something to the technical information about the diff cover but will not market the product or company itself. It is actually currently in the testing phase, so it's not for sale quite yet...

The first picture in this thread posted by @Bahndvr is the finished raw casted piece. The second picture posted by @JohnVallo is the finished piece after CNC detailing. The fins extend about 0.8 inches below the diff itself and are about 8 inches long. There are also fins on the inside of the cover to increase the heat transfer to the outside. So far I have produced 10 pieces for testing. They are casted out of alumium in Germany and then they have CNC work on it for the flange and holes, threads, so on. Right now one person in Germany will test it for me since somebody recently crashed into my car and it will take some time to fix. I also agreed with one person in the US to test it and he will post a review on Youtube. I believe the part should work quite well.

To the more obvious issue that some have already mentioned here - the pricing (@shogun32, @LS_Coyote). The pricing that is posted in the other thread is my intended MSRP. Yes you can get a OEM cover for $70 at a online parts dealer. But you have to consider more. First off all, I am not Ford. I cannot produce quantities of 20,000+ pieces a year with the certainty that they will be sold. And here comes the biggest problem. Instead of using die-casting (low to mid 5 digit tooling cost) like Ford can do for its high quantities, I have to use sand-casting (mid to high 4 digit tooling cost). This is a procedure which is mostly manual labour and therefore expensive compared to die-casting. There exist surprisingly few foundries that can cast aluminium to complex shapes with low wall thicknesses of less than 0.1 inch in some locations and greater than 1 inch thickness in other locations. I tried to locate foundries in eastern Europe to reduce pricing, but the ones that could cast this shape were twice as expensive as the ones in Germany. After casting you have to put this on a CNC machine for the above mentioned details. You need a special fixture for this (more tooling costs) and then they can run their program on the piece at the hourly rates of medium sized 5-axis machines. The last part to consider is that the OEM piece weighs ~4.5 pounds. With the added fins on my cover the weight goes up to ~13.5 pounds. So the material cost also goes up by a factor of 3, which is quite an important factor in high quantity die casting.

Now I am doing all of this on my own risk capital and I have to consider the tooling cost for a relatively low volume item. I mostly designed this part for fun and because its function is key to drive the car rather appropriately for longer periods of time. I would really like to go down with the pricing since I know it would sell quite well if it were to cost half. But the maths in that doesn't make sense. If this piece cools your diff temps properly however, you enthusiast still have a cheaper and less complex (fail-safe and maintenance-free) option to existing diff cooling systems.

 

[shogun32]

It is absolutely a laudable effort. Considering https://www.bankspower.com/c-117-products-differential-covers.html runs into the $400 price point, I take back my quibble. Have you considered simplifying the casting significantly so there is a single flat reference plane, and using the mill to cut the external fins and detail work? Plus then you only need a 2.5 axis machine. I would also project fins under the cover but not forward of the mounting face.

What does your model predict as a BTU/h (or W/m-K) of heat shedding ability?

The other idea I had was to bolt a finned block to the outside edge and use thermal-pads-sheets at the mechanical interface.

Do you have a CAD (IGS?) of the Ford cover or a simplified view of your rough casting?

I think I'm going to take a bandsaw/mill to my spare cover and slap something like this on the back. Assuming it's compatible. https://performanceparts.ford.com/part/M-4033-KA

Edit: sigh S550 is 12-bolt cover, not 10.

 

[LS_Coyote]

Understood! I never think about all these things when buying a performance part. It shouldn't break the bank while adding some performance and I'm happy. Thanks for the detailed explanation

 

[FluiX]

It is absolutely a laudable effort. Considering https://www.bankspower.com/c-117-products-differential-covers.html runs into the $400 price point, I take back my quibble. Have you considered simplifying the casting significantly so there is a single flat reference plane, and using the mill to cut the external fins and detail work? Plus then you only need a 2.5 axis machine. I would also project fins under the cover but not forward of the mounting face.

What does your model predict as a BTU/h (or W/m-K) of heat shedding ability?

The other idea I had was to bolt a finned block to the outside edge and use thermal-pads-sheets at the mechanical interface.

Do you have a CAD (IGS?) of the Ford cover or a simplified view of your rough casting?

I think I'm going to take a bandsaw/mill to my spare cover and slap something like this on the back. Assuming it's compatible. https://performanceparts.ford.com/part/M-4033-KA

Edit: sigh S550 is 12-bolt cover, not 10.

Yes, I did consider a simpler geometry in order to make CNC work easier, but in the end there was no free lunch. Milling the fins would drastically increase the price. You want to cast as much as possible and have it on the CNC as little as possible to make it cheap. Just for extreme example: Milling this out of one alumium block would make the price go over 10,000 EUR for a one off. Extruding the fins forward of the mounting face drastically increases your surface area and cooling capacity. I leaned on AMG and M car design for the length of the fins. For a cheap production they are of course not ideal.

It seems like you have insights into thermo . Therefore, I do hope you understand how difficult it is to estimate or model this and how difficult it makes it to answer you question. The thermal conductivity is a function of air speed and temperautre difference to name a few. In order to get a right figure for the convection, I would have needed to do at least a partial CFD of the cars underbody including the diff cover. Optimally you would want the CFD coupled with heat transfer calculations which is absolutely crazy in these dimensions. But I can provide you rough estimates based on scientific articles of the thermal conductivity. I am an aerodynamicist and not a thermodynamicist so view these numbers with caution. The surface area increase due to the fins is a factor of 2.4. Considering only natural convection on the OEM cover you get a heat transfer on the order of 300 W. With the fins you increase the conductivity and gain forced convection, which has the big part in cooling. This increases the overall heat transfer to the order of 1500 W. Since these are probably terrible estimates, I would put an error bar of +-30 % on both of these figures.

And here are some CAD pictures you asked for. On some pictures it may look like the fins are close to the diff housing. But since the flange is curved it only looks that way. There is a gap of 0.4 inches between the fins and the housing all around the circumference. Also the fins extend only to the face of the OEM cover if that makes sense. So for installation you do not have spacing issues with the rear subframe. The most outside fins have a curved shape and only slightly extend from the surface. This is there to make room for the exhaust.

 

[Bahndvr]

@FluiX are you or someone running this?
Does it clear exhaust pipe?
What kind of temps are you seeing at the cover?

 

[FluiX]

@FluiX are you or someone running this?
Does it clear exhaust pipe?
What kind of temps are you seeing at the cover?

No not yet. The first piece will go on a car in Germany in about 2 weeks. And a person in US will get it at the beginning of September who will test. I will report temperature numbers then. The cover was designed with exhaust CAD data as well and should have no more problem clearing it than the OEM cover. But the first installs will give final confirmation of this.

 

[Bahndvr]

No not yet. The first piece will go on a car in Germany in about 2 weeks. And a person in US will get it at the beginning of September who will test. I will report temperature numbers then. The cover was designed with exhaust CAD data as well and should have no more problem clearing it than the OEM cover. But the first installs will give final confirmation of this.

I think September is a little late but data is data.
I hope the German one has a Torsen as they tend to run hot.
Thanks

 

[FluiX]

I think September is a little late but data is data.
I hope the German one has a Torsen as they tend to run hot.
Thanks

Good point on the Torsen. None of EU cars have a Torsen from factory. But I am putting a Torsen in mine with a 4.09 final gear. The diff is already assembled and waiting to be put in. That will produce plenty of heat. So one piece for testing will also go in my car. But I will not have comparable before and after numbers because from factory the car has a 3.55 gear with clutch type LSD. The only thing I will be able to say is if it works enough to not go into reduced engine power mode.

 

[Michael_vroomvroom]

Very interesting. Will be really welcome (or perhaps I should say, really cool) if a completely passive solution like this turnes out to work well enough. Thumbs up for trying and looking forward to the results.

 

[CVCashmere]

And will it fit on a convertible that has the extra subframe?


thanks

CVCashmere

 

[FluiX]

And will it fit on a convertible that has the extra subframe?


thanks

CVCashmere

I am not quite sure which extra subframe portion you are speaking about. I don't know the extra reinforcements on the convertibles too well. Can you post a picture? Of course the part was designed more in mind for the PP and PP2 (Fastback) drivers who go to the track. But the external dimensions of the diff cover are identical to the OEM cover towards the rear and top of the car. It is only bigger due to the fins towards the bottom and the front of the car. Therefore, I think it will probably fit, but I could verify with a picture.

 

[Falk03]

...I think it will probably fit, but I could verify with a picture.

This is not a very high quality picture, but I guess it will do the job. As the bracket is only beyond the exhaust pipes I would guess, it should be fine.

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