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34 Posts
Discussion Starter · #1 · (Edited)
In hopes to reduce wind drag and also reduce rain water entry into the motor bay I fabricated and installed a belly pan. If anyone installs and finds any errors to the instructions please let me know and I will update.

  1. Fiat 500e abs belly pan fabrication and install approximately 2hrs to fab and install
  2. Modeled from this site: Fiat 500e Front Belly Pan ($55+ shipping)
  3. List of parts: $83
    1. ABS plastic sheet - 83cm x 64.5cm x 2.38mm (32.7" x 25.4" x 3/32") $73 for 4'x8' sheet (I plan to do the rear diffuser later, I had a lot left over)
    2. Bolts M6 - 1.00x25 or Lowes (part image looks wrong) you may only need two of these for the two front mounts. $2
    3. 1/4" x 1-1/4" faring washers $1
    4. Red Loctite - $7
  4. List of tools:
    1. Jig saw
    2. Drill
    3. Drill bit 15mm or 3/8"
    4. Jack & Jack stand or car ramps or drive one side of car up on the curb
    5. Wrench or Socket for the bolts
    6. Latex or similar gloves
  5. Instructions
    1. Summary, cut the abs mount under motor bay. See below measurements. There are two existing threaded mounts at the front of the car that the M6 bolts screw into (mine had nothing mounted to them). There is an existing plastic cover in the center of the car which has 5 bolts holding it on, you'll use the existing two bolts on the front of that cover to mount the belly pan under (closer to the ground so the wind flows over the existing cover). End of install should look like this:
    2. Use Jig saw to cut abs 83cm(front/back of fiat) x 64.5(side)
    3. Drill holes per below diagram, note: I measured twice but did not make two belly pans to confirm the diagram is 100% accurate (sorry if it's off, let me know and I'll update the measurements) if you want to be sure, drill the holes one at a time use the bolts to mount in place to make sure your holes line up. This is what I did and then measured the belly pan outside of the vehicle to create the below diagram.
    4. After drilling all 4 holes, mount with bolts and washers, use red Loctite on bolts. Apply the Loctite the length of the bolt (like ketchup on a hotdog)
    5. Jig diagram all in cm:
    6. CM to Inches:

2013 500e
27 Posts
I've been working on this for a bit, but not as a product. I'm very happy to see someone making this accessible for others. :)
In my version, I've completely closed off the bottom as well as the front wheelwell space.
For the goal of minimizing the mess inside the motor bay, it was important to close off the wheelwells. I got a lot of dirt/sand/gravel from there.
However, closing this off restricted the cooling airflow, which has turned out to be a significant issue. I've done a bunch of testing while looking at OBDII data.
My solution has been to add a vent to the hood, which has solved the cooling problem so far. I've tested it on hot, but not our hottest ( 100+F ) days.

2013 500e
27 Posts
Ok; first I'd like to qualify the pic. It's not the most blingy thing.. I'm planning on anodizing it to match the hood or accent colors.
With regards to aero mods, it's really easy to mess things up and have reverse flows, etc.
In this case there are a few issues that don't give much margin for error.
1) The engine bay is packed with stuff that restricts airflow through the heat exchangers. I've removed a few things, and it's helped with flow & cooling.
2) The hood is very short. If the vent is located too far back, the positive pressure of the hood/windshield area could cause reverse flow. If the vent is too far forward, the flow must reverse direction to make it out of the vent.
3) It's best to minimize the amount of internal structure that is cut for the vent hole.

I purchased my vents from RaceLouvers, a company that specializes in making vents for race cars. They actually do real wind tunnel testing to make sure their products work. They also have a set of louvers intended for Abarths.

I located my vent on the passenger side, where the air would be forced to flow over the charger & help cooling. The charger is last in the cooling loop, so even when it's not being used it heats up from motor/inverter generated heat. Also, when the car is charging, the vent provides an effective cooling boost that reduces cooling system loads.
If more cooling is necessary, I can add the opposite side louver. At present I'm looking into improving the flow in front of the heat exchangers and reducing the inlet size.
Here is a pic of the vent after I got done with pressure/tuft testing:


Bottom line: The motor/inverter stay the same temperature as they did before I added the bottom/fenderwell covers. My guess o' meter's range prediction has extended to 90miles - and this is a 2013 car with some very non-aero performance mods.

2013 500e
27 Posts
Thanks, & now I'm curious what "very non-aero performance mods" you have!
I'm going to try to not pull this thread off topic; I'll post some links to other threads where I detail them.
In general, wheel & suspension mods. Aerodynamically, open spoked wheels pull air from underneath the car, swirl it, then release it out the sides, destroying the smooth flow of air down the side of the car. This is why EV wheels tend to have minimal openings.

2013 500e
27 Posts
More on topic, I have a couple suggestions to improve the underside. I see that this setup is essentially the same as EV-upgrades product. Because this can be a start from scratch effort, it could be much better.
1) Cover the entire midsection between the wheels. The battery supports are aerodynamic disasters. They are essentially 13mm high square edge ribs on an otherwise reasonably smooth surface. This will cause enough turbulence to make any diffuser in the back ineffective. The air entering the diffuser must be reasonably attached smooth flow.
2) Reduce the diffuser angle and maybe cover more of the rear suspension. The sources I've read on the topic (including texts on racecar aerodynamics and wind tunnel tests) suggest a diffuser angle of approximately 7 degrees for minimum drag. The angle can be increased slightly (if there is good flow) for improved rear downforce, but the air must stay attached to the diffuser, or it becomes ineffective. You can see why most "diffusers" in the back of sporty cars are just bling.

2013 500e
27 Posts
Here is how I started things. An Aussie blog on automotive aerodynamics suggested trying stuff with simple/cheap prototypes. My first front covers were made of a foam/cardboard material:

Believe it or not it survived almost a year. :)
I did learn that it was worth working on a better version, and that it would be important to keep the gravel and sand out. Even though it was just held on with the standard Fiat bottom panel bolts and was flexed around my cross-brace, there was no problem with it flapping in the wind.

So rev2 was made of decent plastic. Making it out of ABS like Jimmy0000 is doing would be much better than this stuff I had sitting around. This white stuff is the shower surround material from HomeDepot. It's both heavier and not as impact resistant as ABS.

The bottom is connected to wheelwell side covers, which really helps stiffen both the bottom cover and the wheelwell side covers.
Here is a shot inside the front wheelwell. The covers were made of 1/16" ABS that was heat formed to both make necessary corners and stiffen the pieces. Heat forming is really easy with a heat gun (hair dryer on steroids...)
I also covered the vent in the front. The side cover was made of 3 separate pieces to enable fitment around stuff like my chassis brace, the driveshaft, etc.

Here's a closeup of the front part, fitting around the chassis brace:

Here's a closeup of the back part. I used rubber to get close to covering moving stuff like the driveshaft, swaybar, and steering link:

It's holding together very well so far, and I have no problems with the sand and gravel piles. It's also removable if I need to fix something.
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