DIY Rear, anti airdam (top speed/track mod)

Builds
1

#1 added support with the bumper support gone. And from wind “flapping” at hi speeds. That Ive seen on cars going down the track.

#2 The GP rear is like a ass dragging snow plow for the air under the car. Hopfully better MPG, trap speed. better everywere I see.

The support frame I made. All hand tools, cheap light weight materials for lowes.

http://i2.photobucket.com/albums/y11/studderin/air/IMG_2919.jpg
IMG_2919.jpg800×600

3/4x3/4 alum angle iron. a 1/8x1 bar. And some weied thin alum U channel 1/2x3/8 I belive its panel edging? Cut the 30" I was going to wedge it behind the outer, and infront of the center L tap on the bumper. But it bend over my knee nice [:)]. So I just gave it the nice curve that matched the arc of the bumper.
http://i2.photobucket.com/albums/y11/studderin/air/IMG_2923.jpg
IMG_2923.jpg800×600

Top support, is 3/4 x 3/4 alum angle, going off the outer muffler bolts. And itjust happends to be on the same plan as the pinch weld for the trunk floor and the spare tire wheel. So I got some 6-32 nut/bolts on the weld seam in the middle.

Then I made some conection brakets that come out really nice.

http://i2.photobucket.com/albums/y11/studderin/air/IMG_2924.jpg
IMG_2924.jpg800×600

http://i2.photobucket.com/albums/y11/studderin/air/IMG_2927.jpg
IMG_2927.jpg800×600

I cut them out so after I bent the angle they touched for added support. Sence I can’t weld alum. Plua this is low buget, so Im just useing 6-32 machine screws for harwear, and #6 sheet metal scews for the skin.

mad a cender brace with the curve of the skin, and a ataching bar.

http://i2.photobucket.com/albums/y11/studderin/air/IMG_2932.jpg
IMG_2932.jpg800×600

Than made a carboarded tempate for the skin. And traced it on some shitty acrillic plasitc I bought. I knew acrillic is the shittiest sheet plastic for working with but it was so cheap ($8?) 48x48. over 48x36 .025 alum that was $60. I cut it with my jigsaw at hi speed, and a super fine blade. And suported it well, and it still started cracking and spider web cracking all over. I bend it into shape just to test fit it better. But drilling holes it will crack all the hell. Im got get some softer polycarconate tomarrow and make the rest of the skins.

then center main skin just sitting there

http://i2.photobucket.com/albums/y11/studderin/air/IMG_2948.jpg
IMG_2948.jpg800×600

what the air seeing under the car

http://i2.photobucket.com/albums/y11/studderin/air/IMG_2955.jpg
IMG_2955.jpg800×600

Im gona make a skin peice for over the tip cutouts. The a outer skin for the sides to the wheel wells. tommorw after work.
Will track test it for back half gains if I have time.

discuss.
will it create lift and make the rear unsafe?
or will less air drag under the car, give it the wing profile effect and more down force (never gone to school on this I dono?)

2

Should cut lift, which effectively “adds” downforce.

3

its not an anti-air damn, its a defuser
anywho, :tup: to DIY

4

if you see any benefit from this i will be shocked.

5

I won’t be. Cutting “speed holes” in the bumper adds 1-3mph in the quarter. This should be just as effective (or maybe more), but isn’t as ugly as speed holes.

Shit, you’re an engineer. Think back to fluids or something. That bumper was basically just a parachute before.

6

yes, but it also creates a quiet zone for air flow…

Example: Pickup trucks get better gas mileage with the tailgate up.

7

is this true? what about with a toneau cover?

8

they did it on mythbusters.

EDIT: looking at the shape… the part you made may effectively ADD lift

9

I think you have the right idea by making some sort of skin to attach to your mounts. Stop the air from getting caught in there all together and I think you can see benefits. As a bonus, add longetiudinal flaps so it can act like a diffuser and speed up the air flow even more. I think you’re on the right track.

10

I agree, judging by the harsh angle, I can see the rear being more squirly at speed with this. You want an undertray that goes under the chassis at a gradually increasing angle as it gets to the rear. Not something that drastically changes airflow like this, which is exactly what I mentioned to Mark online. Oh yeah, and I dont care how many MPH they give you, speed holes are FUCKING GAY.

11

I think the boundry layer. or whatever the corrent term is for the pickup truck effect. Isn’t gona be worse with it. Then not having this is the rear.
Even on the car stock, thoues 3 molded plasitc tabs that have shitty push pins into the bumper support. Leave a 5-6inch gap that air gets trapped in. And the rear bumper flaps in the wind at speed.

Ideally I’d cut out the spare tire well, and make it smooth form the rear cradle to the bottem of the bumper cover. To get a less sharp angle I’d have to go around the spare well. thats a huge PITA. I made a carboard temlate doing that. I’d have to use sheet metal screws into my truck floor youd see. And they cut up the grociry bags:).

The top half has the steeper angle. The lower curves to more flatter blend to the bottme of the bumper cover. Looking down under the car, the bottem 4-6" is the only real direct area. I’m sealing off the upper part just for added strenth. And to seal it better so its hopfully just stall air up there anyway.

The drilling holes works good but it dosn’t look stock, and I didnt wnat to ruin a good bumper cover. Lonie with a turbo neon picked up 2 mph back halfs just drilling some holes. And a 1stgen neon dose have the low ground effect shit this car has. But this is differnt so Ill have to find out myself, just looking for imput/thoughts form some the the tech guys on here. thanks

12

that last pic Im really sticking the camra up behind the rear cradle. Generally the mufflars/ and the spare tire well look like the bottem plain of the car.

The ass spolier thats gona make lift. I was thinking about too. Im hoping just the bottem edge gets direct flow air. So it dosnt have much force.

lowering the car might be the best affect on airflow, but you run into breaking axles alot more. Stock height the CV angles are strait, But the front of the car dose raise a few inches on slicks. So that should get it back to stock CV angles? So that should blance that out? But its still alot higher ratio of people with faster gtps having cv boot, and axle probelms with lowerd cars. Over stock right hieght cars.

Heres a pic I took at NYI of the GMracing fullrace build orange cobalt LS turbocar. it has a full belly pan. Pretty pimp. I was surprise to see it.

13

These were a big PITA to do. But came out really nice 1st try:)

http://i2.photobucket.com/albums/y11/studderin/IMG_2977.jpg
IMG_2977.jpg800×600

I see NYSpeed has a DIY section. Thats so good, Im not sure if you wnat to move it there. I havnt tested it yet. So no real tech info.

14

:word:

15

:tup: to the diy and :tup: to Mythbusters.!!! i saw that one (trucks)

16

Bumper support, maybe. Airdam, definitely not. Rear Diffuser… nope, at least not in it’s current state.

How well do you think that will hold up if someone rear ends you at say 30 mph?

Can’t wait to see the “tests”.

17

You should put side skirts on that come down to the ground, then put a shop vac in your car, cut a hole in the floor board and suck the air out from underneath it…

Sound Stupid?

It was attempted and banned from F1, as im sure it is from every other form of racing.

A rear diffuser attempts to do this but less effectively… the faster the air moves under the car, and the slower it moves over the top of the car the more downforce youll create…

The full underbody pan on the cobalt drag car you posted i would assume does that more so for the reduction in drag, then it does for downforce… but it accomplishes both. Because drag increases exponentially with speed, it is more important to reduced drag the faster you go. Unless you need 5 tons of downforce to keep your tires from spinning like the top fuel guys.

A rear diffuser is for downforce more then it is for drag reduction…

18
19

i agree as well…its like flaps on an airplane wing…to me it seems like ur angle is the opposite of what u need…the part attached to the bumper should be higher than where it attached under the car…if ur spare tire well is lower than than the bumper u should attach it there some how…but i could be tremdously wrong cause my logic isnt always that good

20

Pretty much. when the Chaparell hit Can Am, people were throwing fits.