# closing grill and bellypan - worth doing?



## dtbaker (Jan 5, 2008)

I am wondering if anyone has 'real life' results showing the effect of closing off the front grill and/or adding a full or partial length bellypan for improved aerodynamics.

Since my average use is 'suburban' with average speed probably around 35, with fairly frequent stops at intersections and lights, I am wondering if it will have any noticeable effect....


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## Guest (Mar 20, 2009)

At minimum you might consider the belly pan. Should be pretty easy to do. On what kind of car do you want to close the grill? Plastic front end? Metal? Usually the grill will be closed if you plan on doing plenty of high speed driving. Your driving should pose no real issues.

Pete : )


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## Guest (Mar 20, 2009)

Well I took a look at your little EV. Looks like that vehicle might have a pretty flat underbelly anyway. How bad is the undersides of one of those little cars? Might find some sort of aluminum or something you can form to shape and rivet in place to close off the grill. The put on the grill cover to hide the ugly rivets. 

Pete : )


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## dtbaker (Jan 5, 2008)

gottdi said:


> Well I took a look at your little EV. Looks like that vehicle might have a pretty flat underbelly anyway.


The front (under the motor) is pretty 'lumpy' and probably has a fair amount of turbulence even at low speeds. I am probably going to do that section no matter what just so I can protect my motor from the occasional water splash, mud, snow, etc.

The front 'grill' used to funnel air thru the radiator, and looks like a nice 'smile' with my white battery cases showing thru, but I m wondering if sealing it over would help the airflow enough to make a discernible difference in efficiency at 35mph. On a bicycle I kow that aero effect starts adding up at speeds over 20mph, but on the absolute horsepower scale its pretty small... noticible on a bike where you only have 1/3 hp, but pretty small percentage on a car using 10-15hp on a flat road just from the frontal area.

The mid section IS pretty smooth, but the the tail behind my battery box could act as a fair 'parachute' the way the rear bumper scoops down. I left bolt threads sticking down from my battery box thinking that I would use them to fit a pan to....

In my case, both front and rear bumpers are un-painted ABS. I bought a sheet of black ABS with a belly-pan in mind. Its easily heat formable, gluable, and heat-weldable.... Attaching should be easy, I am just wondering if anyone had a real-life numbers to show effect.


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## Guest (Mar 20, 2009)

At speeds under 50 you really don't need to do any of those things. Covers for water and mud protection is a good idea and should be done. Just be sure you still get proper cooling for your motor. I would not bother with the grill unless you plan on driving at higher speeds. 

Pete : )


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## mattW (Sep 14, 2007)

I disagree, I think a grill block and belly pan will make a significant (~5%) improvement in range. Even if aero is only a third of your losses at 35mph, something in the order of 20% of the drag in an ICE car is due to cooling. A perfect sealed bay would get 7% better efficiency at those speeds, I think 5% is probably doable.

Darin from ecomodder.com does some pretty extensive testing on his ICE metro and he found the following:


> *2.3% = *gain from outside mirror changes
> *2.3% =*gain from partial boat tail prototype
> *2.2% =*gain from undertray
> 
> ...


So 5% sounds about right for a grill block+undertray albeit at slightly higher speeds


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## esoneson (Sep 1, 2008)

I suggest that you check our *ecomodder.com*.
The guys there know every trick in the book about how to reduce coefficient of drag. And you will be surprised at how much energy you can save with a few simple things like blocking off the grill and belly pans.
Also, even if you think that the belly of your vehicle is 'relatively' smooth, you should consider covering with aluminum (as suggested above) or some other covering, just check out some of those guys results.
What I am saying is, that it WILL make a difference, especially at highway speeds.

Eric


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## dtbaker (Jan 5, 2008)

mattW said:


> Darin from ecomodder.com does some pretty extensive testing on his ICE metro and he found the following:


very interesting.... I am thinking that perhaps I need to develop a better test and measurement method so I can more accurately report effects in my case.

There is a stretch of road nearby about 3 miles long with no lights or intersections and do an out-back at a steady speed.... what would be suggestions on the most accurate way to measure actual kWhr consumption accurately?

I have been using the energy IN from my wall with the kill-a-watt meter divided by trip odometer. This is start-stop at my house, and would be thrown off by getting there and back. Also not exactly the same charge cycle probably.

Is there a cheap meter I could attach to accurately measure kWhr actually consumed during a set test course?


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## tj4fa (May 25, 2008)

I would recommend closing off the grille and belly for rain/water purposes except maybe for any air ducting to the motor bay/controller that you might need to keep things cool.


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## Roderick (Dec 8, 2013)

It's been 7 years since the last post...any updates or recent discovery on regards with improving efficiency of our cars? 
I am still in middle of converting my car and since all modern cars have started to introduce grill closing systems I thought we should add some ideas into this thread! 

Rui


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## dougingraham (Jul 26, 2011)

With conversions you are kind of stuck with the aerodynamics of the OEM. Sure you can add a belly pan and you can mostly block off the grill area and you will see a small improvement at highway speeds. The faster you go the more it will help.

Unfortunately, going from 100 to 102 miles of highway range is just not significant. You can blow that increase away with just a couple of mad dashes from 0 to 60 or even just driving a little faster down the highway.

I mention the following because the Tesla Model S has blocked air intakes and a smooth belly. My Tesla can do maybe 200 miles at 80 mph. If it is cold or I have a head or cross wind or there are lots of hills along the route then I wont make 200 miles. If I drive at 25 mph I can go ~450 miles on that same charge. Similar ratios will apply to any car. I can't see ever driving anywhere seriously at 25 mph but you can see that slowing down has a dramatic effect on range. In the Tesla the range does go down if you go slower than 25 mph. The parasitic losses become significant at slower speeds. I read somewhere that Tesla wanted to eliminate the side mirrors in favor of a cameras and screens because it would give them a 3% increase in highway range. Since cameras and little screens are so cheap why didn't they? Because it isn't DOT approved right now. Unless you have a safety inspection that would ding you for not having external mirrors I suspect this would be a fairly simple thing to do and have as much impact as the belly pan or closing off the grill.

For around town driving it is far more important to lower the mass of the vehicle. Since this is where most all of our miles are driven in our DIY cars, this is where I would spend my time and money. But this is a lot of work and expensive. With an enormous amount of effort and an outlay of several thousand dollars I figure I could remove ~200 lbs from the weight of my EV RX-7 by replacing the hood and fenders with carbon and the windshield and hatch glass with polycarbonate. This would give me an almost 10% increase in range around town. It isn't worth it though. At the present cost of electricity I could never make back the cost. 

I am not saying you shouldn't do it. Just that you have reasonable expectations for the amount of work it will take.


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## Matej (Dec 4, 2015)

Not sure what tests people have conducted, but I would think that properly routing the air in and out of the engine compartment could be even more beneficial than closing the grill off completely. Especially since most conversions still retain the motor in the engine bay.

Other than the obvious weight reduction, lowering the car, and making it more aerodynamic, you can also get rid of any 'parasitic' electronics to lower the 12V accessory draw. You can also replace all incandescent bulbs with LED's and the headlight bulbs with a 35W HID kit. Just make sure to get quality LED's that are bright enough and shielded HID bulbs so you do not blind people.


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## evmetro (Apr 9, 2012)

I run the same donor chassis as the original poster, and have done the modes that he was asking about. I reconstructed the bumper with no air openings, and brought it up in the middle between the headlights to meet the hood.










I did a belly pan as well, and based it off of the new 3" lower height of the bumper that I constructed. Having the belly pan a little lower than the original floor allows the control arms to settle up and flush with the belly pan so that the wind does not hit them. I don't see much gain cruising around town, but there is a significant difference on the freeway. I switch back and forth driving my various ICE and electric Metros, and I can feel a big difference with the mods when I am descending steep grades at high speeds. It makes 80 mph feel like a smooth and natural cruising speed, but when I am in my ICE Metros 80 feels like it is fast as it can possibly go, which it is. Even higher speeds are still very quiet and smooth, but I have nothing to compare to, since the ICE Metros don't go that fast.










.


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## madderscience (Jun 28, 2008)

my xB has a OEM lowering kit, closed off grille, aero mirrors, and a partial belly pan. The sum total of all of this equates to (gut feel) about 7-10% improvement in range at freeway speed (60mph). Net cost in terms of weight is about 20lbs, virtually all of that is the belly pan, which is made from 1/8" ABS plastic rigid wall of a collapsible swimming pool. I could make it lighter, but the plastic was free.

In order of effectiveness (most to least), I would probably say: 

1) lowering
2) mirrors
3) grille block
4) belly pan.

The belly pan starts aft of the engine/motor compartment and goes til just ahead of the rear axle beam. If it covered more of the forward area it would probably be more effective.

One thing I'd like to figure out how to do is make rear wheel skirts. Doing this would require drilling holes in the body though, which I don't really want to do.

More info on my site at http://amphibike.org/blog/scion-xb-ev/scion-xb-ev-construction/ev-aerodynamic-improvements/


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