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Old 05-25-2008, 01:38 PM   #1
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custom undertray project

i've started another thread on this on ecomodder, but i didn't want to keep the gassavers out of this

this is a sort of prototype... if this shows some improvements i might build an aluminum version that's twise as long and that spans the full width of the car. i didn't want to get the coroplast to close to the exhaust and in front view the added area would be minimal





the bolts are secured to the tray with a standard nuts and than to the brackets with a wingnuts, if you undo all the wingnuts the whole things falls off without the risk of loosing a nut or any problems reattaching. the brackets are made from card slot covers from the back of a PC (source: garbage at work) wich are bend to shape and have a couple of holes drilled in

btw wingnuts are fairly expensive (5 nuts cost as much as 22 standard nuts and bolts from the same manufacturer)...still if i save 2L of gas with them i've got my money back!

the second picure also shows my custom wheel dam

BTW; i wanted to have dome shaped bolts but they had this square bit below the bead that was taller than the envisioned thickness of the whole tray so tha'd be a problem, so i got standard head screws (wich where also cheaper) i did however align the scew slots with the flow direction might as well do things rightwhen you can
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Old 05-25-2008, 09:06 PM   #2
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that's looking awesome. I too know the power of the PC slot covers When it stops raining I hope to do something similar to my GP. Keep us updated on the changes it makes.
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Old 05-26-2008, 03:14 AM   #3
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drove it for the first time to work today. i don't have instant FE feedback so reliable fe figures will take some refills to show.

i must say i noticed a difference althoug it's hard to say what exactly it was. one thing that really stood out was engine noise was much decreased.

my engine is not the most powerfull so combined with a short fist gear it revvs rather high when takeing of from standstill, however with the fairing on noise was much decreased.

as far as drivability... it felt a little "heavier", i'm not sure if that's downfoce, added stability or just plain drag (wich would be strange but not impossible) initially i thought the cars felt a little slower but when i reached a the onramp of a bridge wich is rather steep the car seemed to go faster than it usually does and i had to break to get to a speed i'm more comfortable with in that steep cuve.

temperatures might be a hair higer but nothing spectacular.

so overall a good first impression but it will be down to the FE results to see if i'll develope it further.
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Old 06-11-2008, 03:02 PM   #4
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alrighty, this is the result of two evenings work and a lot of planning in advance, still, most of these things where improvised after lots of test fitting, takeing measures etc. and getting inspiration as i went along



the only real mistake so far is a single hole in the wrong location... thats a, um...speedhole

the holes where not drilled but i used a self tapping wood screw, i used a hammer to punch trough the metal and than just screwed all the way in, and than used a bigger screw to get the right size. this gave the holes a nice bulge on the inside so the final screws will be a bit recessed.




the tray is basically a sheet aluminum of 0.5mm of 100x50cm, cost me about 12? (actually my grandfather was with me at the time and he insisted on paying for it, although he didn't really get what the plan was).

i basically chose it as it was both the lightest and cheapest, but on top of that, it's also extremely pleasant to work with. it can be folded by hand over a table edge and metal shears cut trough it like paper.

the sheet was very floppy at first, but after all the folds notably folding over all the sides it's pretty solid. it'll need some reinforcements in the center, but overall it feels like some sort of oven tray. also most of the remaining sharp edges of the folded lips where folded over again, wich gave even more strength and eliminated dangerous sharp points.


the cutouts at the back are for the exhaust and to direct some air to the oil sump. my dad seemed worried it would get hot, so i'm not takeing any chances.


the shape follows the profile of the bumper and blends this to a straight line.
working on the undertray i noticed how neath everythings placed under my car, still i started thinking about maybe extending things further



the tray doesn't reach all the way to the sides but this is good i think as that will form some natural brake cooling ducts, i'll rework my wheel dams though so that they allow cooling air fro the brakes to pass above them but direct most of the air to the undertray.

now i only have to work out the attachment method (i might end up drilling two holes in the subframe...my dad says that would be ok) but a more sturdy version of the original method is also possible.

since i took the original tray off to work on this one i've been driving around without it for two days, boy does that feel bad, some sort of A-B-A testing.
i don't know what this will do for my fe, but i can tell an undertray sure can make a car feel more sable and quite... still a 1-2% improvement in FE will have the tray pay for itself in less than half a year so whats to loose.

hope i can finish it tomorrow.
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Old 06-12-2008, 10:07 AM   #5
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that looks really nice for being doen without a bender. good job.
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Old 06-15-2008, 03:09 PM   #6
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i finally got round make some more tweaks to it and install it on the car.

i ended up drilling 3 small holes in the subframe to fasten it at the back. i drove it for some short distances... stays on fine so far, but it tends to rattle a little bit on uneven ground, or when slamming the door... nt a problem but it shouldn't be difficult to cure.

the car feels stable, but i can't say driveing is much altered... it doesn't coast notably further as far as i can see so it remains to be seen how effective the mod is.... also i took of my weel dams as my dad feared they might prevent propper break cooling, although i expect them to be back in a revised form.



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Old 06-20-2008, 05:45 AM   #7
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Wheel dams are not hugely important; if you use them fair them off so that they supply plenty of air to your brakes.
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