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Old 11-01-2010, 09:22 AM   #11 (permalink)
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Here is a link to a rear belly pan I built a couple of years ago for an Echo.


The rear of that car has very poor attachment points so I built a simple frame with thin aluminum extrusions that I purchased at Lowes. These thin extrusions can be bent a bit into gentle curves and can be pop riveted or screwed together to form a basic structure for coroplast.

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Old 11-01-2010, 10:34 AM   #12 (permalink)
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added this thread to our wiki:
Belly pan - EcoModder
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Old 11-01-2010, 10:39 AM   #13 (permalink)
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puddleglum and jimepting,

Thanks for those links to your projects. I added them to our wiki list

Do you have user data to enter? Like what MPG you gained?
If you do please add it to the wiki or post it up and I will add it in for you.

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Old 11-02-2010, 10:14 PM   #14 (permalink)
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I made a coroplast & aluminum flashing undertray similar to basjoos:

Looking aft:

Looking forward:

(Note, everything aft of the muffler is part of the bottom of the prototype boat tail.)

It's been on & off the car multiple times: for testing; to apply anti-rust treatment to the car; and because I won't risk crossing the Canada/US border with it on the vehicle. (I just assume it'll get me flagged for further unnecessary inspection.)

Mine is directly attached to the floorpan/underbody and other existing hard points with machine screws.

You can't see it well in the photo, but the front section is cut out where the exhaust down tube goes horizontal into the catalytic converter, and also a bit aft of it. There's about a 1 inch margin around the metal. Aside from that, it completely covers the engine bay.

There are cutouts to permit full lock steering of the front tires.

The control arms of the independent rear suspension are fully covered, but they still have full range of motion because the coroplast is layered at that point (think shingles) so that as the suspension moves the control arm up & down, the layers slide.

Results: I measured a 2.2% improvement in fuel economy @ 90 km/h (56 mph) in an A-B experiment. See http://ecomodder.com/forum/showthrea...9.html#post873
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
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Old 11-02-2010, 10:59 PM   #15 (permalink)
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I have links in my signature below
MetroMPG: "Get the MPG gauge - it turns driving into a fuel & money saving game."

First: ScangaugeII

Second: Grille Block

Third: Full underbelly pan

Fourth: rear skirts and 30.4mpg on trip!
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Old 11-07-2010, 12:23 AM   #16 (permalink)
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Originally Posted by Weather Spotter View Post
puddleglum and jimepting,

Thanks for those links to your projects. I added them to our wiki list

Do you have user data to enter? Like what MPG you gained?
If you do please add it to the wiki or post it up and I will add it in for you.

Unfortunately, I was under a time constraint when I built my pan so I didn't get a controlled A test to do a proper A-B test. Also, I had been running a poor front quarter pan for a couple of years and a front air dam for several months previous. Still, based on highway trip mileage numbers,I'm consistently seeing at least 3-5% (1-1.5mpg) improvement at 65-70mph.

Almost all my driving is done 1-5 miles at a time.
Best short trip: 2.4 l/100 km, 3.9 km
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Old 11-07-2010, 11:05 PM   #17 (permalink)
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The under belly plate is going to be my project this week. I've been looking at a few ideas. My primary concerns are how I can easily remove it for servicing my vehicle, and the rigidity of the design.

To me, an underbody cover that vibrates in the wind is less efficient than a rigidly attached one, not that I'm saying other designs will vibrate, but zip ties seem like a less-than-rigid mounting system, even if pulled tightly.
I think I've come up with a good plan.
An aluminum sheet (or perhaps 2 depending on how I'll work around the exhaust pipe) attached with hinges with removable pins. Half the hinge can attach to the car's underside with a spot weld, and the other half can be welded to the pan.
Removal is easy, as you just pull the pin from between the hinges and the pan drops right off.

I'll let you know how it goes..
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Old 11-08-2010, 10:32 AM   #18 (permalink)
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BZP T-100 (2010) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
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I put in two cross members that does exactly that...but I had to bolt the belly pan in because I didn't want just anyone removing the pan with ease...
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Old 11-11-2010, 12:40 PM   #19 (permalink)
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Thumbs up Here is what worked for me

1) Any vehicle likely needs a frame to support the belly pan from above. Has anyone built one that attached directly to the car's underbody?
-----I attached mine directly to plastic plugs under the car from the manufacturing process and a plastic fairing in front of the fuel tank and into the bumper plastic at the rear. I added aluminum flashing fender liner extensions in the rear wheelwells to seal off the belly pan and give me other attachment points. I used an external support strap of aluminum about half way back because the factory plugs were too far apart. I drilled NO new holes in the car sheetmetal.

2) How to attach framing and sheet material? Rivets? (aluminum or something else??) Sheet metal screws? Rubber well nuts, aka expansion plugs?? Something else?
-----I used screws designed for metal roofing. They have a hex head and a washer with a rubber washer underneath, and they are self tapping into the plastic plugs. I did use an anchor screw into one of the forward body plugs. I fashioned a couple of brackets out of aluminum strap to support the coroplast in a few places.

3) What framing and sheet materials did you use? What worked and what didn't work?
-----I scored a donated 4x8 coroplast election sign. It seems plenty sturdy, light and best of all, free! It was big enough to cover from the back bumper up to the catalytic converter.

4) How did you deal with the engine bay, between radiator bottom support bracket and the firewall?? Were you able to put a panel over the area, or at least over part of it?
-----My car came with a factory belly pan under the engine, which I replaced with a sturdier aluminum skid plate. I added coroplast wings? to fill between the bumper and the front tires, attached to the front fender liner lip.

5) How did you deal with the exhaust area? I'm considering leaving mine uncovered (it goes down the center till it gets near the gas tank) but what did you do? If car has a rear muffler, did you cover it over?
-----I had previously removed the muffler and put on a straight pipe (It really is no louder than stock in the Turbo Diesel) to give a more room for a flatter upslope from beneath the rear axle to the back bumper. I covered everything except about a foot where the catalytic converter is. Caution! Those things make some serious heat! some places farther back I'm sure the coroplast is in direct contact with the exhaust pipe and I have had NO melting or even discoloration of any kind. Your results may vary.

I did not do A-B-A testing after 2 days of rolling around on a mechanic's creeper to get it installed but I had my first 900 mile tank since I have owned the car. My fuel log shows a very low tank mpg for one particular trip but that was in the name of science. I did some high speed testing of the belly pan and everything held up fine. (Still going strong even in snow and ice)

I would rate this mod as very successful. Mine was minimal cost, totally stealth and has made a big difference in my highway mileage.
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.

Last edited by COcyclist; 02-10-2011 at 11:41 AM..
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Old 11-12-2010, 10:01 PM   #20 (permalink)
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After reading many threads about bellypans, I finally started construction of one on my 2010 Toyota Venza.
My wife wondered why we have a new car and I "need to work" on it. ) She knows I can't leave a car stock ...... need to "Personalize" it.
I'll take pictures on Monday(11/15) when its on the dealers hoist.
We will be giving it a 3000 mile test starting 11/22/2010, hopefully there will be an increase in MPG.

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