Old bed liner for belly pan
 

For my black Bronco II 4x4 I would like to add a front belly pan but haven't found anything cheap or strong enough to cut up. Then I noticed there are lots of used plastic (abs?) bed liners on CL for $50 and up. There would be a lot of material left over maybe even for an air dam etc. Btw, I'm not expecting miracles for mileage but since I have ordered an Mpguiino or whatever it's called I can do some ABA tests. All of the bed liners I have seen have ribs on the bottom so I was wondering if that would be bad for use as a belly pan. Thank you.

I think it's a great idea! Glad you thought of it.

Thank you. I think I'll give it a try. The underside of this Bronco looks pretty "unclean" to me due to the ifs. The front differential is nearly a flat surface hanging down 12" below the frame. At least the old straight axle 4x4's had a rounded housing. Would having a belly pan that starts at the existing bumper/spoiler and angles down to cover the axle work instead of adding an air dam? I've been reading all I can on this forum for about a year but don't recall seeing that discussed.

Seems like a good idea to me. Easy to cut and drill, but still stiff enough. And if you get really excited you can shape it some with a heat gun.

I bought a bedliner off of ebay for $.01 ...and it was local pick-up!

If you are suggesting using the bedliner from below the bumper angled downward, it sounds like a better design for an off-road skid plate than for improving aerodynamics. Big Dave on this site has had good success with a big air dam on a full size truck. I really do like the idea of repurposing a discarded bedliner as belly pan material. Could you try an airdam and a lowered belly pan below the differentials like BamZipPow's Toyota?

Thank you to all for your comments. I hauled the free bed liner home today. Also I received my MpGuino fuel mileage gauge a couple days ago and got it hooked up today. It is working great! Still need to build a case for it and calibrate it a little better but the fuel mileage it is reporting seems pretty close to what I had determined previously. The front bumper is 18" from the ground and the front differential is 9" from the the ground. What I am thinking about is using the front part of the bed liner as an air dam and letting the lower part serve as the belly pan. My two concerns are: 1. Is the curved transition from the air dam to the belly pan a bad thing? 2. Is having the air dam and pan 9" from the ground too high to be effective? Incidentally the bed liner is the same width as the front bumper so it can wrap around the sided but the tires will stick out about 3" on each side. I'll try to get some pics tomorrow before I start wacking it up.

That is a really good idea! If there is anyone in the Vancouver BC area that wants to try it, I know where there are a bunch of old bedliners that could probably be had for free. PM me if you want to try this out.

I assume your plan is to make the vertical cab-side part of the bed liner serve as the air dam? If so, the curve would be minimal, not enough to worry about. Great idea!! As for ground clearance, if the bottom is smooth, more can be a good thing. Think Aptera or Sunracer.

Here is what I've been doing. As mentioned above, the air dam and belly pan are one piece. The dam is 10 inches tall leaving 9 inches of ground clearance in the front. For now I think I'll cut the belly pan off about a foot behind the front tires. After the pics I used screws and washers to fasten the new air dam to the exiting small one. Not sure if I should try to angle the bottom of the dam toward the rear of the Bronco or leave it vertical. The whole thing should be easy to remove.

Thats a very nice Hilux! I had a '78 but traded it for a Karmann Ghia a year ago. I miss that truck but that was the best Ghia I'd found in 10 years. You cant keep them all.

I've been thinking that on a solid axel truck you could wrap the axels with sheet metal to make an airfoil and have a smooth pan against the frame but I dont think a Bronco 2 sits up that high.

Yeah that's my ElectraHilux. I should be be finishing up the conversion instead of working on this Bronco :)

Keep it vertical.
The purpose of an air dam is to reduce the amount of air going under the car - pushing the air to the sides or even over the top.

Angling the airdam to the rear will make it easier for the air to slip underneath it - exactly what you don't want.

Ideally you'd want a clean separation between the air going underneath the air dam and the air being pushed aside by it - that's where splitter plates come in, forcing the air to go either way.

Without a splitter plate, some air is going to spill underneath the dam.
A more rounded transition should result in a smoother (but slightly bigger) airflow going underneath the air dam and onto the belly pan.

that actually looks pretty good, most aerodynamic cars and suv's seem to have an undertrat that angles up to meet the front bumper in the middle, i think the rounded transition won't be a bad thing, and the ribs are nice too.

what you may want to do is add some extra dams in front of the tires, google some random suv pictures or even recent sedans ( a mercedes c class for example)
and you'll notice the center of the airdam is a little higher and seems more inviting to allow air undermeath in a smooth way, but the area in front of the tires and suspention looks more agressive and obstructive... you don't want air to flow into the tires it seems. it looks like the sides of the dam don't cover the full width of the tires.
you may want to try flaring them out somewhat if possible, or adding something to them to achieve the same effect, but than again, adding the dam will improve over stock and without a wind tunnel perfect aero will be impossible to achieve anyway

Great advice gentlemen. Would it help the separation if I install a flat piece of 1/8" thick aluminum fastened to the bottom. edge of the air dam that protrudes a couple inches in front of the transition? Also should I bend the corner of the dam to blend with the fender and perhaps use the front half of a fender flare to divert air around the tires? One other thing, I removed some 80's style aluminum running boards. Should I put them back on (I could paint them black) and try fill between them and the sides of the belly pan? Notice in the picture below the vertical flat pieces that that stick out past the fenders. Not sure if that is good or bad.

That would give a clean separation between the air that goes underneath and the air that's pushed aside.

The air dam should only be about as deep as the lowest component that catches a lot of air underneath the belly of the truck.
Making it lower will increase the total frontal area of your truck, and that creates more aerodynamic drag.

Shielding the tyres from the air also helps cut down on aerodynamic drag, but make sure you don't increase the frontal area of the truck too much by doing so.


Basically, anything you do to smoothen the messy airflow underneath the truck should help.

Look for user BamZipPow's Toyota truck.
He's covered the entire side area between front and rear wheels.

Another modified truck to look out for, is aerohead's T100 truck.

So would it be better to raise the air dam a few inches and let the belly pan bend downward under the diff? Also I think I can flip the top front section of the bed liner and use it as a small air dam chin or whatever it is called.

Love that old Toyota HiLux. Air dam looks good too. :D

I cut the dam off two inches in height got it all fastened down with screws in the dam part and heavy plastic ties (rated at 175 lbs) for the belly pan part. Still need to add the chin. I used a sawsall and a small sabre saw to do all the cutting. A step bit worked really well for drilling the holes. So the pan bows down about 3 inches as it passes under the front diff and bows back up about the same distance once behind the diff. Should I have kept it at the same level after the diff?

I think this could wind up being a nice-looking aero piece (not that it matters in some respects); more factory-like. Re-purposing, and the benefit of appearing as-if factory-made from some angles. Way to go!!

The ideal, as far as I can understand the science, would be to have the pan level with the front dam until it passed behind the rear diff, after which it should gently slope up. Like the other chaps have said, the purpose of the air dam and splitter is to make a clean separation of the air-flow, so by introducing an angle at the front, you might well be messing it up.

Whether or not the difference is measurable, I don't know, but that's how I understand it. Anyone, please feel free to correct me.

As the belly pan is angling down to clear the differential, you could have kept the air dam at a length that clears the diff - as it gives the same frontal area.


If only the diff is sticking out underneath, you could look around for some streamlined shape / bulge that could cover it, then make a hole in the belly pan, and cover the hole and the diff with the streamlined shape.
That way, you'd be able to raise the belly pan back to horizontal, and only increase the frontal area right where the diff is, and not over the entire width of the truck.

just a thought that popped into my head, but wouldn't a good compromise to streamline "stuff" (like a dif )portruding from the undertray be to build a boattail for it? some L brackets angled towards eachother might be a good idea... ok it's a detail and the effect might not be measurable, but on the other hand it seems like a simple thing to do that's practical (some cheap plastic L brackets that can be screwed to the undertray behind an inperfect portusion...

just a thought

I flipped the top part of the bedliner and trimmed the edge to make a serve as the "chin". It is hanging about an inch below the bottom of the belly pan. I left enough length to allow me to adjust it up and down temporarily. Probably look better if more was cut off.

Inventive ;)
That should do the job.

How does it look from the front ?
It'd be good if the air dam also shielded most of the wheels.

down
 

My pan angles down to the bottom of the axle allowing better ground clearance in front of it.Then shallow diffuser behind axle.
Note of caution.ABS is a thermo-formed plastic so you'll want good heat shielding near cat-converter/exhaust pipe/muffler or she might revert to pre-formed sheet,and in turn,buckling the pan.Ouch!:o

Here is the front view. Notice I covered the grill to see if that helps I imagine having tires exposed and also the body being open on the sides isn't helping much. Before I can do some ABA tests I need to get my MPGuino recalibrated since I just replaced the faulty fuel pressure regulator which was sucking into the intake. I modified a new one to make it adjustable so I could lower the pressure a little since it was running rich in open loop.

dam
 

yeah,it would be better if the dam wrapped around to completely shield the tires,but you should see an effect for sure

Grimm, it looks great with the chin splitter and almost factory. I think you will see an improvement in highway mpg.

Kammback idea
 

In the spirit of waste not want not I have been toying with ideas of a Kammback for my Bronco II using wheel wells from the old bed liner. I can piece two halves together together to make one piece. I have no idea if the angles would be right. First two pics I had one direction and the next two I turned it around. I know I know the tire has to go :)

Haha! I do like the Kamm-back idea, you're one resourceful chap :D Of course, I think that a smoother angle would be much more effective, however, your simple idea may allow a small amount of flow re-attachment. Also, it should go some way to reducing flow spilling onto the spare, so you may well see and/or feel some improvements. A-B-A tests will be necessary for hard evidence, so get that MPGuino calibrated :thumbup:

All in all, a great little project you have there. Keep up the good work.

I'm thinking of using it in the direction of photo #4 and cutting the front so the top angle matches the top of the hatch. Then cut the bottom off at about 45*. I saw a pic of a Kammback on a minivan somewhere and I thought that was what it looked like. Could be a total wasted of time for all I know.

Waste not want not is a great motto and I think you've done a good job on repurposing the bed liner for your pan and front air dam. But, IMO, I think your trying too hard by trying to use the wheel wells for a kammback. It just doesn't look like the right shape to me to be effective, judging from what others have done. Here's a suggestion (hope you don't mind), why not see if you could use the wheel wells to make some rear wheel covers and maybe something to smooth the air flow around the tires. I suspect you will see more benefit for your effort from that. Building a kammback is a good idea, I just think that the wheel wells are not the best choice for material. Good luck on you project.

I appreciate any advice since I am new to this. After reading the following topic it appears that a box like my Bronco II probably would need a full boat tail to see much improvement.
http://ecomodder.com/forum/showthrea...box-14168.html

Search for the streamlining template on ecomodder.
That's the shape you want to approximate with the extension.
The better you match the template's angles (in both plan and side-views), the better it'll work.
But even when done crudely with flat plates, it'll work to some extent.

Obviously, in the real world it'd get too long to be practical, so you need to cut off the streamline extension.
The cut-off at the rear should be sharp and abrupt so the air separates as cleanly as possible.

Search for other folks' Kammback (or Kamm-back).


Reusing things is OK, but I think you're stretching it a bit ;)

Thank you for that. After looking at the templates I realized that the Bronco might be more efficient driving in reverse :) Anyway I have moved on to trying to direct the air around the front tires. Then maybe some side skirts?

First fender flare
 

I cut out a couple flat bedliner pieces and used a heat gun to mold them for front fender flares Probably need a support to keep them flared out in direct sunlight. They're quite rigid after they cool.

Way to go. :thumbup:
Not perfect, but it'll do better than what you started out with ;)


If you make sideskirts, you can make them do double duty as rear-wheel flares.


Some ideas :
Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - aerohead's Album: Pickup images

here's a few more idea's you might considder,
http://i77.photobucket.com/albums/j5...distance-2.jpg

the green dams would have most effect along with possibly some sort of side skirts. measuring the height of these dams on normal vehicles could give you an idea on minimum ground clearance for normal driving

making the wheel wells more tight would also cut some turbulence as would adding smooth hubcaps. rounding the A pillars could help to, although that's a bit speculative.

anyway, just a little fun i had after seeing your great work.