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Anyone made a full underbody piece?

Old 08-15-02, 10:52 AM
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Anyone made a full underbody piece?

Have any of you made a custom underbody piece to keep turbulence down underneath the car? I would think even a simple flat sheet of ABS would do the trick. Sort of like the front splash pan on the FC; but just continue it back the rest of the way. Maybe this is not needed, but I would like any input from others. I personaly do not like the look of wings and body kits, so to me this seems as the best way to increase aerodynamics without effecting appearence (or drag).
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Old 08-15-02, 11:18 AM
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Been thinking about it, but no time.
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Old 08-15-02, 11:27 AM
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well there would be the problem of exhuast burning it up if it is all the way from front to back.
Technically you would need it for rear-axleback. But I would like to know how or where I can get one as well.
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Old 08-15-02, 04:20 PM
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I think the designers use the transmission tunnel as a venturi to pull heat out of the engine compartment. So closing off the entire underside of the car might be a problem unless you provided for this also.

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Old 08-16-02, 10:23 AM
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Vents could be easily incorporated into the design. And for what I am thinking; if it got damaged or even slightly melted, it would not be a disaster since it would be a cheap plastic part. I would give it a shot if I could find a place to by large sheets of plastic. One flat piece cut to fit between the frame rails and simply bolted on. It would weight less than 10 pounds and be very inexpensive; maybe $30-40. So you could make one and trace it out onto maybe 2 or 3 others, and that should last you for awhile.
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Old 08-16-02, 10:25 AM
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I am more concered about whether it would actualy help aerodynamics in any meaningful way.
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Old 08-18-02, 09:25 PM
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I am very close to embarking on (hopefully) the building of a two-piece undertray. Yes indeed it helps aero. The idea is move the air as quickly as possible from underneath the car to make it a low pressure area thereby making better use of downforce applied through the body itself and any aero additions.
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Old 08-19-02, 11:46 AM
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I've been considering something like this for awhile too, but I think ABS isn't going to do it for you. I was thinking sheetmetal, because it won't melt, and it's more durable. Of course it's going to weigh a little more. You're going to want to make sure the material is strong enough that it doesn't start oscillating under the pressure differentials on the top and bottom of the sheet (AKA it either needs to be very solidly backed by the car undercarriage or strong enough to not deform under the pressure). Ideally it would also have a raked tunnel from the axle-back, giving you low pressure and rear downforce. I think it's a great idea, but you know, if you make an actual, working aero piece, and it fails when you're relying on it (high-speed corner), you've got a good chance of crashing…So proceed with caution
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Old 08-21-02, 11:31 AM
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1/8" thick plastic sheets can be bought from amco or go to your local dirt track racers shop. that is were i bought mine. the most logical is to mimic the skyline r34's use of just front and rear diffusers. the front is fairly easy, however the rear has to be cut well around the exhaust. the front is the most important due to all the crannies that create drag and turbulence. however make sure that the rear of the engine bay is able to vent as that is were much of that hot engine bay air goes, not to mention if you close of the engine bay where will the air flow through the radiator go?
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Old 08-21-02, 03:40 PM
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I am in the process of making one from fiber. it has low pressure areas to suck the car to the ground like the indy cars. My major problem is the heat from exhaust. I have alos had to put it on hold while I move into my new house.
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Old 08-22-02, 09:19 PM
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haha... this is so crazy, 'cause I was thinking like two days ago.
Last weekend I was walking through the paddock at Mosport, talking to some Porsche team when I noticed their underbody thingy lying on the ground.

It had ducts built in, sort of like the "cheese grater" ducts on the stock FC underpan. It was made entirely from carbon fiber... they had applied (aluminum?) tape where the exhaust exits (obviously would need to be replaced with something more permanent on a street car)

I was thinking of maybe just re-doing the front underpan of my FC, making an almost exact copy, but with more precisely located vents (the porsche only had 2 vents under the engine...) as well as a rear carbon fiber duct... (maybe covering as far as the axles)
There really doesn't appear to be too much disruption through the center section of the car... other than the catalytic convertors (hmm... maybe those just... uhmm... dissappear... )
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Old 08-29-02, 09:57 PM
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Check out the article on the new Nissan 350Z in Sport Comapact Car ( I think...). Nissan has reall worked on the underside of the car (as they did a bit on Skyline) to kill lift. They suceeded in zero lift in front and zero in back w/ another optional package.

The article shows the tray, bottom of car and odd little strategically placed items that do the trick on the 350Z.
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Old 08-29-02, 10:09 PM
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I ended up working on a design in AutoCAD as well. I've gathered lots of pictures from different sources and it seems that they use aluminum tape/fiberglass shields around the exhuast area to keep the CarbonFibre cool. I will post more info on this as i get close to end of design.
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Old 09-16-02, 01:57 AM
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why not just have the strip underneeth the exhaust be made of sheet metal and the rest be made of fiber?
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Old 09-18-02, 09:45 AM
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This is interesting... I'm yet another person who's been thinking of this.

... why would you need to heat-shield the carbon? If you use the right resins, it's pretty damn heat resistant on its own, isn't it?

Of course, the problem with covering the exhaust up like that would be more heat in the passenger compartment... like, if the heat can't be radiated downwards as easily, and doesn't have as much air passing over it... well, I guess it's going to go up.
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Old 09-18-02, 03:59 PM
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Just a thought but - If you are going to goto the trouble of adding the full underbody piece, wouldn't it be easier to just keep the air from going under the car to start with? Something like (no flaming here) a NASCAR type air damn that goes almost to the ground. Some type of air splitter could be added to it if needed. Maybe I'm missing something here but it works for their 200 mph cars. Is the underbody piece going to be used on a street driven car or a dedicated racecar? If a racecar do the rules allow the addition of such a piece? I'm just curious.
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Old 09-18-02, 06:35 PM
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you mean an air dam like on RX-3
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Old 09-27-02, 11:53 AM
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Originally posted by FPrep2ndGenRX7
Something like (no flaming here) a NASCAR type air damn
No not nascar... but I am thinking GT style...

Ok again we have a common thought... my buddy and were thiking bout making these in fiber also... How effective would this be? ANd fiberglass should be heat resistant enough I would guess.... as for the design, all one huge piece from the fron to the back? Or else I was thinking bout a diffuser like this one for the third gen...

http://www.importfan.com/product.asp?0=360&1=375&3=2802

Last edited by Sammymatik; 09-27-02 at 11:56 AM.
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Old 09-28-02, 06:25 PM
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damn... if i had a 3rd gen, that would be my first upgrade... mmm... racecar-ish...
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Old 09-29-02, 12:56 PM
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a front splitter will help tremendously with keeping air out from underneath the car. a good set of very low side skirts help alot also in creating suction towards the ground. an underbody piece should be your last modification as it won't produce as great an effect as the other two, it won't produce downforce, just keeps the air already under the car from getting really turbulent as it flows over all the crap on the bottom.
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Old 10-11-02, 02:45 PM
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I've thought about this for almost a year now, but I just haven't had the time to really work anything out just yet. I'll probably just rebuild (read:get a new) front underbody panel, a front lip spoiler, and a rear diffuser. It's a street car that I plan on using in AutoX so I wanna keep it clean, almost Lotus 111S like :-).
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Old 10-11-02, 03:40 PM
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If you're going to make it, use aluminum at least something as thick as 0.60. cheaper than carbon, and yes carbon will transmit heat and electricity very well, it is after all pure carbon. Added bonus of aluminum, it will deflect some instead of breaking like a fiber product. and if you're low enough it will shoot sparks. Maybe thats not that great of benefit, but oh well.
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