aluminum undertray advice wanted
 

i'm toying around with the idea of an aluminum undertray, that will attach to the subframe and slope slightly down from the front bumper as does the subframe, so it will shield the engine carter, transmission and exhaust from the airflow.

the undertray will have to be easily removable from underneath the car.

right now the attachment method i envision are U frames that hug the sides of the subframe and that are rivetted to an aluminum sheet, however this would make it difficult to remove.

so i'm looking for some inspiration from real world examples.


what i want is something that won't fall off out of itself but can be easilly removed without leaving to much traces when needed.

can i just hang something from a subframe or would this disturb the cars handling etc?

for now i'll work on a simple temporary solution to see what the effects are

I'll be putting mine on with tapped holes and bolts. However, I fastened my coroplast tray that is under my engine bay with sheet metal screws into the plastic bumper cover, and I used plastic expanding fasteners into the existing subframe at the rear.

how about using that stuff that tears apart easy, i dont know what its called but its got hooks and a fluffy part that it clings to... just uuse a whole crapload of that stuff...

you mean velcro? usefull stuff but i doubt it will hold an aluminum plate on maybe if i cut slots in it and use it to tie loops around the subframe... still it doesn't strike me as something that looks very solid...

did you drill holes in the subframe or did you use existing ones? i'd rather not make any structural alterations to such a load bearing structure... well i can't really as tech inspection would not allow it.

http://i17.photobucket.com/albums/b5...g?t=1211215968 I went a different route. I used Lexan for durability here in the front I used the bolts and plate for the tow hook to secure it and sheet metal screws into the existing plastic undertray.

I'm curious whether a commercially available rally skid plate might fit this description.
http://www.writerguy.com/primitive/i...1;800x600].jpg

If you can't drill the subframe, how about using epoxy to attach flat head bolts to the frame, then use (nylon insert) locknuts to hold the belly pan up? That will not impair the strength of the subframe, and if done neatly, will not raise any eyebrows at a safety inspection.

I've started taking some welding classes to tackle problems like this. I have a little more room under my truck to make the belly pan rounded though. You may try making a small frame (7/8" Unistrut) that bolts to the cars frame and then attaching the metal to it. Maybe with dzus fasteners.

I emailed the rally skid plate manufacturer. He indicated that some people have claimed a 1-2mpg improvement, but didn't seem to want to promise anything. He and a colleague did indicate that some additional vibration or noise might be noticed.

For easy on and off of a body panel, its hard to beat Dzus fasteners. A flat head screwdriver is all you need to remove the panel is about 30 seconds. Faster if you can move quickly. The downside is you will need to weld on your frame.

You can also get them with tabs you can turn without a screwdriver.

http://www.southco.com/landingpages/dzus/

these Dzus things look pretty handy but as you say they don't really do ways with the need for welding.

today i tried to fit a piece or corrugateded plastic underneath the car. it's alost exactly the width of the subframe. i might hang it from the frame with zipties if i can find some big enough aroudn the house. i can't make it go all the way back as the exhoust would probably mely it (or set it on fire wich is the last thing you want)

it seems i could get aways with one or two attachement points under the bumper.

and some "hooks" to suspend it from the subframe at the rear.

i'll see if i can safely put this together in the next few days and what the effect on FE will be, depending on the results i might choose to get some sheet aluminum and build an upgraded version, but than again, if this version works well enough i might keep it as it is.

does anyone know how hard sheet aluminum is to work with and how one would go about bending and cutting it to shapes? would some metal shears work? i wouldn't mind invesing a little money in a need mod that has proven to work; but i wouldn't like mess up to much of the aluminum

These are nice. They make nice cuts and its like a hot knife through butter with sheet aluminum.

http://www.toolbarn.com/product/kett/KD-442/

Hand shears would work, it would just be harder, and more annoying/painful. For bending a table with a sharp edge and a mallet works.

@adrive7 looks like a fine tool, but it's a bit expensive... it would sort of cancle out any financial saveings the undertray could have. if this thing delivers an actual 1% improvement in overall FE it might pay for itself 1 or two years... of course the higher fuel prises go the sooner it'll pay off, and i hope i'll save more gas, but it's not that big an area so i try to be realistic.


for the construction apparently sometimes it also pays of to look at a problem from the other side... i always envisioned the tray had to be removable from below, but when i opened the hood i saw there was plenty of room to reach down so i might suspend the undertray by just slideing it underneath the back of the bumper, suspend the other side from an alluminum L beam that rests on top of the subframes at the back and than use a conveniently located screw in the middle to hold a bracket that the whole assembly from shifting backwards and detaching.

to attach everything i'll drill holes trought the undertray, put some bolts trought it from below, and secure these to the tray with nuts from the top and than run these trough the L beam and the bracket and finally secure them with wing nuts.

to detach the undertray i would simply have to undo a couple of wingnuts and the whole thing would fall off with all the bolts staying in the undertray. i'll use some rubber wachers to dampen the vibrations a little to keep things from shakeing loose.

since te aluminum sheet might be a little floppy (i'll go for the things i can get as thats cheapest and lightest!) i might need to rivet some L beams along the edges.

anyway that's the plan.

i think i'll construct the frame and than cover it with some corrugated plastic. if that gives some measurable gains i might build a more solid version.

ok enough said, here's my first attempt.
http://i77.photobucket.com/albums/j5...a/DSC02023.jpg

i used a piece of gorrugated plastic from a sign and some metal brackets made form these little things that back off unused card slots at the back of a computer.
http://i77.photobucket.com/albums/j5...a/DSC02021.jpg
there whas a single bolt sticking out the botton of the radiator frame (it holds a bracket for the power steering line...edit: looks more like a water hose in the picture...that'll probably be it...whatever) it stuck out just far enough to accept my own bracket and another nut.

next i slid the coroplast sign underneath the bumper and folded the bracket down so it toughed the plastic. i'd already drilled two holes in the bracket so this location was marked and than a bolt was ran trough the plastic attached with a nut and than through bracket and secured with a wingnut. basically that made sure things would stay in place but the fairing was still a little floppy at the back so i bolted two more brackets on top of the plastic that squeeze it against the subframe. undo the wingnuts and it all falls clean off.

the faring isn't as long as i'd like but the exhaust would interfere, and while i could cut a hole for it, it would still represent a fire/meling hazard.

also the sign only covers the center section and not the sides, because, well that was the size of the sign. on the final aluminum version (if this one shows it's worth persuing the idea) i'd make it both wider and longer with a cutout for the exhause.
http://i77.photobucket.com/albums/j5...a/DSC02028.jpg
at the front there where some holes in the radiator support. i cut out two holes in teh fairing that match up with these. they seem to evacuate air before the radiator, wich is a little odd, but i suppose they're there for a good reason so i don't want to mess with them.
http://i77.photobucket.com/albums/j5...a/DSC02030.jpg

it's still a little floppy at the front but so far i'm rather happy with it. lets hope it does something good!

as a final note, i'd initially planned to use done headed bolds for a little extra aero, but than i realized these had a little square extention below the dome that was taller than the thickness of the aluminum so the nut would never work.. so i went with standard screw heads. i did align the slit for the screwdriver with the airflow... that a few mm less frontal area ;) im a bit perfectionistic sometimes.

undertray
 

Lots of good suggestions by members and I'll add what I did to the soup.Fortunately for me,the Toyota had all kinds of frame rail penetrations already in strategic locations.The holes were large,however by filling the big holes with suitable flat-washers,then capturing those from both sides with even larger flat-washers,I was able to attach hangers for my belly-pan by through-bolting, without drilling or welding.And a note of caution: the frame is hardened steel and if heated,can loose strength,and yield at a lower load.If you simply have to weld,use TIG or MIG to localize the heat and keep some wetted heat sinks surrounding the area to conduct heat away to the environment.Remember too that you have the potential for fire and explosion if any part of the fuel system is compromised.Angle metal can be attached to the hangers with bolts.I recommend nylon-insert nuts,as they cannot inadvertedly come loose.The angle metal can be drilled for skin attachment,and speed-nuts,from auto parts or auto refinishing supply provides an anchoring point in lieu of Dzus fastener weld-on backing plates.Also,light metal angle can be pop-riveted to the aluminum sheet to create modular panels which can be attached as a unit.I've used this since the 1970s and never had a failure.Aluminum is prone to fatigue fracture and needs to be securely fastened.Big fender-washers are handy at attach points,as they distribute fastening force over a broad surface area.Whatever method you use,just make it tough and strong and avoid some of the stupid moments I've encountered over the years.

Have you had any problems with the ladder frame flexing against the tray and fasteners? Are bushings needed?

i'm wondering about that too, not the tray is plastic so it'll flew pretty easy, but on the final version, it'll be an aluminum sheet framed by small aluminum L beams...that'll be pretty stiff.

i'm also wondering if i might need to design an radiator air exit duct in...i might just get away with a top grill block, but the grills are pretty exactly sized, and it doesn't make sence to try and smooth out the airflow under the car and at the same time obstruct the flow trough the car, wich already had a hard time.... or would that needlessly complicate things?

here's what i've made so far

it's a 0.5mm 100x50 cm aluminum sheet, cut and folded, the folds really give it much more strength and rigidety than i expected.
http://i77.photobucket.com/albums/j5...a/DSC02167.jpg
http://i77.photobucket.com/albums/j5...a/DSC02168.jpg
http://i77.photobucket.com/albums/j5...a/DSC02172.jpg
http://i77.photobucket.com/albums/j5...a/DSC02163.jpg

Nice,,,you have a brake ???

I like that skid... I need to find some coroplast political signs to hack for the Neon...

nope, just folded everything with my hands over the edge of the workbench or along some metal bars... the folds are not perfect, but thats mostely because the edge of the bench was chipped. in the places where i needed a real tight fold i rubbed the handle of a file back and forth while applying pressure

this stuff is just great to work with, making this out of carboard would be more difficult.

the folds also make it pretty rigid... it will need some support in the center to keep it form makeing noise on the car though.

the holes where not drilled but i just punched a hole in with a big self tapping screw and a hammer and than screwed it in all the way, and than used a bigger screw to get the right size... worked faster and more presise than a drill... this method along with some hamering of the spot with a big bolt, provided a nice recess where the screws can sit.

i've been driveing for two days without any tray, and i can honestly say, the difference is big! the car feels much less stable and more noisy, can't comment on FE changes yet though, can't wait to put this on thoug!

finisched!
http://i77.photobucket.com/albums/j5...y/DSC02185.jpg
http://i77.photobucket.com/albums/j5...y/DSC02182.jpg
http://i77.photobucket.com/albums/j5...y/DSC02181.jpg
http://i77.photobucket.com/albums/j5...DSC02174-1.jpg

well you did good :thumbup:

Can you please clarify the above? Are you saying no tray is worse than the political sign? Thanks!

The final result is shiny so it must be good.

no at the time of the post i was still working of the aluminum version, and had taken of the plastic one, so for a few days i was driving with the car in stock configuration (appart form wheeldams wich i'm reviseing too)

when i originally put the first tray on i thought driveing had changed, but things like "stability" are difficult to feel when you're driveing day to day... on a windy day any car might feel less stable, but when i took the tray off again i did get the impression the car drove worse again, so i really think it did something good.

although things are not dramatic, i don't think the average person would detect if its there or not from driveing the car...

now i've been driveing for a couple of days with the aluminum version. so far it's been grate apart from a rattle when a smam the door, wich makes the car sound cheap, but a little rubber in the right place will cure that.

i get the impression the plastic version might have been a hair better at sound proofing, while the aluminum version seems to keep the heat in the engine bay longer, wich is nice.
i'd driven the car and parked it outside at my girlfieds home, quite a while later we drove of and i remember being surprised the engine was warmer and the car drove nicer right away.

i've considdered placeing the plasic tray inside the metal one to get both the sound and heat insulation, but perhaps i'll use the plastic for a rear defuser so we'll see.

i still can't comment on FE changes...haven't gone trought a full tank yet, and it'll take a few tanks to be certain it works (i drove half this tank without the tray and half with so this resuly might not show the full effect although in theory it should be slightly better than average)

as you can see the sides are still exposed. yesterday i made some plastic spacers to fair these over and to serve as a basis for better wheel dams.
i don't want to compromise brake cooling though, as i damaged a break rotor once on my last car, so i know it's possible!

i think i'll make an opening above the wheel dam so the high pressure will force air in, this will also eliminate some lift.

i hope the tray will help so i don't have to start looking for a design flaw or take it of, we'll see

"i don't want to compromise brake cooling though, as i damaged a break rotor once on my last car, so i know it's possible!"


How did that happen? It would be nice to know, for us folks that are thinking about moon disc wheel covers & etc.

Thanks,
Rich

well i'm not saying one has to do with the other, but

i had smooth wheel hubs installed from my dads retired ascona (nephew of the old chevrolet cavelier), wich look more or less like a moondisc but with vent holes at the sides, i also had an airdam extention in font of the wheels, the wheelwels had no liners in front of the tires (stock setup) so behind the bumper everything was pretty much a see trough affair...wich would not make speciffic break cooling paths needed, but might also cause hot engine air to migrate to the wheelwels.

it happened on a trip to the ardenes in my old kadett, we where going to say in a guesthouse at a farm for a weekend with some friends, it was a couple of hours driveing highway, and than some large open roads but more hills, mostely high speed driveing so i think the brakes would have been rather hot to begin with.


suddenly the GPS send me on a little road wich i though would be a shortcut to another major road but the quality of the road continued to decrease, wich got me a little agitated as i was beginning to suspect the GPS from not sending me along the best route (it turned out other people's gps from a different brand had indeed taken a better route). my girlfriend started jokeing about running a flat etc, wich didn't really help to improve my mood at the time, anyway.

suddenly there appeared a very big pothole in the road, so a slamed the breaks however with all the small rocks on the roads i skid trough it.

i feared the worsed but when i got out of the car everything seemed fine, however when we got on our way i noticed a vibration in the steering wheel everytime i used the breaks.

this vibration didn't go away, so when i got home i took of the wheel and noticed the contours of the breakpad where visible on part of the disc, i don't think the disc itself was really warped but you can tell that from just looking at it... it appeared some break pad substance was baked onto the disc.

my dad said it wouldn't be a huge problem and since i switched to another car shortly afterwards i didn't fix it, but if the discs where indeed damaged that would have been an expensive repair.

anyway.... it's one of these things that remembers you that various components on a car can get hot and that they can get damaged pretty easy under such conditions.

perhaps the mods to the car had nothing to do with it but that would only mean that these things could occur even faster when factory cooling would be decreased...

since then i try to see why engineers made a setup wich seems to be causeing drag... rather than assume everthing that sticks out into the airflow is just a design flaw... you might not be able to tell a break cooling path from all the other mess on the bottom of the car, untill you close it and the breaks overheat... wich doesn't mean things can't be improved

It kinda sounds like you had some abnormal driving conditions.
All that heavy breaking during a short time frame can't be good, even for brakes that are getting good cooling air.

In any event, I'm pretty sure I'm not going encounter those conditions, but on extremely rare occasions. :turtle: