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Old 11-05-2008, 04:53 AM   #11 (permalink)
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I used aluminium sheeting leftover from a cladding job at work. It's about 1mm thick and is quite light although a full car undertray might weigh a bit with all the fixings included. I just covered under the engine and from the back axle to the bumper. Improved coast distance noticeably but cabin ventilation is terrible. The exhaust vent is in behind the bumper and vents out in the space behind the rear wheel. I had to install some flexible ducting to continue it to the undertray but is still not good. Windows fogging up a lot. Anyone have any ideas how to make a passive exhaust vent?


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Old 11-05-2008, 05:03 AM   #12 (permalink)
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perhaps there's not enough pressure difference to draw the air out of the vent.

i'm not sure what the setup looks like but if you place a small dam in front of the air exhaust this will create a low pressure area behind it wich will draw the air out.

this will work especially well if the undertray causes the air to flow faster in that area.

this setup might add a little drag but it will be marginal and you might not have to run the fan as much
aer·o·dy·nam·ics: the science of passing gass

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Old 11-05-2008, 04:22 PM   #13 (permalink)
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Originally Posted by cfg83 View Post
That's it. I really don't have the best memory.
Latest mods: 3-cylinder Mitsubishi Mirage. EcoMods now in progress...
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Old 11-06-2008, 06:10 AM   #14 (permalink)
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Originally Posted by fanamingo View Post
I tried this same approach when I attempted a grill block a few months ago. I was able to achieve the exact shape I wanted, but the block wasn't very stiff when dried. I did about 8 layers of paper followed by 1 layer of an old cotton sheet. Not enough? Or was I missing something else?

For anyone else trying this, wear latex gloves when working with the glue. It turned my fingers orange and it took several days for the color to fade.
Never had my fingers turn orange but yeah gloves are worthwhile.

The mix sounds pretty close to what I have used in the past but I have also used some varnish mostly as a water proofing surface so that may have helped.

I have always tried for some sort of curved surface as well since papier mache is very flexible in flat sheets.
Maybe some sort of strengthening rib is needed behind to add some support and rigidity?

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Old 11-06-2008, 04:16 PM   #15 (permalink)
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I had tried an exterior waterproof wood glue. This may be the reason my fingers turned orange? I may try again at some point with a few more layers and a coating of varnish. I also have a nice supply of coroplast (thanks to a local overfunded election campaign) that I might incorporate for some more rigidity.
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Old 11-06-2008, 04:54 PM   #16 (permalink)
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Getting back to the original focus of the thread, there are several examples of underbody panels linked on "60+ Efficiency Mods".

60+ Vehicle modifications for better fuel economy - EcoModder.com

Here's another coroplast example:

And here's the first car MetroMPG was referring to, which used window screen and paint:
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Old 11-08-2008, 01:20 AM   #17 (permalink)
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I wonder - on the screen application - would a smearing a denser material say rubber cement or spraying some sort of undercoating work better?
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Old 11-08-2008, 02:41 PM   #18 (permalink)
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Originally Posted by Sunwapta View Post
Yes - "flap in the breeze" and then tear or wear rapidly. Glueing, riveting laminating on nylon strapping might do the trick.

There's kevlar, nomex and probably lots of others - at a price.

Back to my list - I'd think the underbelly spoilers would be the easiest modification. You could probably pull those old aluminum rear spoilers off wrecked suburbans, etc. and retrofit them underneath at a mild downward angle. Or just stretch across some tin flashing and bend it down where needed to smooth the airflow.

hey - maybe retrofit a couple of those black plastic hood protectors/ bug deflectors (go underneath and bolt a couple on upside down).
Neighbor Bob built doped Dacron over welded EMT skeleton bedcover for his Chevy truck.It was very rigid considering the scale of materials and very lightweight.------------ No doubt,a bellypan could be constucted likewise,with appropriate heat-shielding where necessary.With quarter-turn Dzus fasteners and weld-plates,it would be easy-on/easy-off.

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