Can I extend the "stone shield" plate to cover my diff

JayW1

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I am converting to side exhaust and while thinking about my options to cover the rear exhaust hole I am considering putting a piece of aluminum sheet extending from the stock plate under the transmission to the rear bumper fascia (mounted to the bottom of the frame).

I am hoping it will improve the air flow under the car and it will also give me something to attach a rear panel to fill the exhaust hole without drilling a bunch of holes in the bumper fascia.

Does anyone know if covering this area will reduce cooling to the differential that could potentially lead to early failure? Any other potential problems with doing this? Will drilling and tapping very small holes into the bottom of the frame to secure the aluminum cause any significant weakness in the frame?
Any insight into these questions would be appreciated.

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This is the area I am thinking about covering.
 

dave6666

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Use the rear pipe hanger bar for your block plate mount. Drilling and tapping the frame shouldn't weaken it within reason, but it would be stronger to weld in nuts. Weld nuts they be called. You could easily put some NACA ducts at the forward area of your plate for diff cooling, or simply rely on the air that has passed the tranny to do the job. That air of course first heated by the engine, then the tranny, and now cooling the diff. NACA ducts are cheap.
 

dave6666

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Here's a couple pics of a weld nut I used on repairing a stripped exhaust hanger thread:

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And how I used the rear pipe mount bar to fasten my diffuser to cover the rear exit hole. You could easily use that mount to fasten your plate.

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Tom F&L GoR

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Use the rear pipe hanger bar for your block plate mount. Drilling and tapping the frame shouldn't weaken it within reason, but it would be stronger to weld in nuts. Weld nuts they be called. You could easily put some NACA ducts at the forward area of your plate for diff cooling, or simply rely on the air that has passed the tranny to do the job. That air of course first heated by the engine, then the tranny, and now cooling the diff. NACA ducts are cheap.

The differential will get hot - surprise you if you touch it. Cooling will ensure normal fluid life. Too hot will smell like sulfur.

I added a NACA duct because I went from Gen 1 sidepipes to the Gen 2 diff-hugging rear exhaust. Dimensions are such that I attached the forward edge (the wide part) to the trailing edge of the trans pan, then the tube aims up at the differential nicely.

However, since I mostly drive the car, I didn't take pictures. :drive:
 
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JayW1

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Use the rear pipe hanger bar for your block plate mount. Drilling and tapping the frame shouldn't weaken it within reason, but it would be stronger to weld in nuts. Weld nuts they be called. You could easily put some NACA ducts at the forward area of your plate for diff cooling, or simply rely on the air that has passed the tranny to do the job. That air of course first heated by the engine, then the tranny, and now cooling the diff. NACA ducts are cheap.

Thanks Dave. The rear exhaust hanger bar would be a good alternative. Since I didn't remove the heat shielding, I didn't even know it was there. A duct built into the aluminum sheet is a good idea as well. The pictures are great and I appreciate you sharing them.

Tom brings up a good point about the exhaust being near the diff and removing the rear exhaust may remove enough heat to cancel the effect of covering the area without the rear exhaust. I wish I would have recorded some diff temperatures before I removed the rear exhaust and I could have compared them to temps without the exhaust and then with the new aluminum belly pan. I think I will work on a rear exhaust hole patch first and then worry about covering the area later. I am also considering a rear diffuser.
 

Tom F&L GoR

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If I had a green Viper I wouldn't leave it sitting around either. Might come back and find white hood vents installed. :rolaugh:

Truth be told, the NACA duct under the car is white. Since it is not exposed to sunlight, I don't have to manage triangulated wave planes in curved time spasms and it has the acceleration effect of self-aligning only the atmospheric carbon dioxide molecules. In oversimplified terms, it shoots dry ice at the differential.
 

Viperless

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Bottom of my '09.

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Tom F&L GoR

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I admire you modifying an '09. How much of the belly pan is stock (asked the '94)?

For the engineering nerds, a NACA duct dimension can be replicated with this info: (white paint finishes it off)


from Carroll Smith's "Tune to Win"
 
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JayW1

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Thanks for that pic Viperless. It is obvious that the engineers felt that the diff would need some extra cooling and that configuration looks very easy to replicate.

The NACA duct dimensions are great as well Tom but fabricating that would be a little tougher unless I could find one already built that I could just attach to the belly pan. Anyone know of a potential supplier?
 

Tom F&L GoR

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Pegasus - NACA Air Inlet Ducts

Get the white ones.

Making it is easier than you think. (But hard to argue about buying one for $25) Draw the 1/2 hour glass outline on the metal. Cut the three sides, leaving the small, leading edge part attached. Bend the larger end upward (toward the diff, if you are cooling that) and add the sides with simple upright sheet aluminum. I did this in front of the hood scoop on the replica Cobra I built.

 
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JayW1

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Looks great Tom and you are right, your method of doing that wouldn't be bad at all. Not that anyone would see it but if I do this I will do it your way. The off the shelf plastic ducts don't look good enough for a Viper. Thanks
 
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