# DIY Rear, anti airdam (top speed/track mod) **URL:** \ **Category:** Builds\ **Created:** [October 20, 2006, 8:24am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056 "2006-10-20T08:24:13Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Studderin](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/studderin/32/7197_2.png) [@Studderin](https://forums.speedlife.net/u/Studderin)\ **Post date:** [October 20, 2006, 8:24am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/1 "2006-10-20T08:24:13Z")
#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](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2919.jpg) 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](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2923.jpg) 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](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2924.jpg) ![http://i2.photobucket.com/albums/y11/studderin/air/IMG_2927.jpg](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2927.jpg) 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](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2932.jpg) 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](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2948.jpg) what the air seeing under the car ![http://i2.photobucket.com/albums/y11/studderin/air/IMG_2955.jpg](http://i2.photobucket.com/albums/y11/studderin/air/IMG_2955.jpg) 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?) ---
**Author:** ![brent\_strong](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/brent_strong/32/7203_2.png) [@brent\_strong](https://forums.speedlife.net/u/brent_strong)\ **Post date:** [October 20, 2006, 8:25am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/2 "2006-10-20T08:25:03Z")
Should cut lift, which effectively “adds” downforce. ---
**Author:** ![Zer0DazE](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/zer0daze/32/7624_2.png) [@Zer0DazE](https://forums.speedlife.net/u/Zer0DazE)\ **Post date:** [October 20, 2006, 8:29am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/3 "2006-10-20T08:29:20Z")
its not an anti-air damn, its a defuser anywho, :tup: to DIY ---
**Author:** ![newman](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/newman/32/7569_2.png) [@newman](https://forums.speedlife.net/u/newman)\ **Post date:** [October 20, 2006, 8:30am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/4 "2006-10-20T08:30:12Z")
if you see any benefit from this i will be shocked. ---
**Author:** ![brent\_strong](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/brent_strong/32/7203_2.png) [@brent\_strong](https://forums.speedlife.net/u/brent_strong)\ **Post date:** [October 20, 2006, 8:32am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/5 "2006-10-20T08:32:16Z")
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. ---
**Author:** ![newman](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/newman/32/7569_2.png) [@newman](https://forums.speedlife.net/u/newman)\ **Post date:** [October 20, 2006, 8:34am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/6 "2006-10-20T08:34:04Z")
yes, but it also creates a quiet zone for air flow… Example: Pickup trucks get better gas mileage with the tailgate up. ---
**Author:** ![Willybeen](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/willybeen/32/7351_2.png) [@Willybeen](https://forums.speedlife.net/u/Willybeen)\ **Post date:** [October 20, 2006, 8:44am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/7 "2006-10-20T08:44:04Z")
> [@newman](#): > > yes, but it also creates a quiet zone for air flow… > > Example: Pickup trucks get better gas mileage with the tailgate up. is this true? what about with a toneau cover? ---
**Author:** ![newman](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/newman/32/7569_2.png) [@newman](https://forums.speedlife.net/u/newman)\ **Post date:** [October 20, 2006, 9:02am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/8 "2006-10-20T09:02:37Z")
they did it on mythbusters. EDIT: looking at the shape… the part you made may effectively ADD lift > [@mythbusters](#): > > Tailgate: Up or down? > > Myth: Driving your pickup with the tailgate down gives you better fuel efficiency than with the tailgate up. > Test Setup > > Adam and Jamie were each given identical, new model pickup trucks. They both had equal mileage, same tire pressure, and 30 gallons of gas. Jamie drove with the tailgate up and Adam the tailgate down. > > The rules: > > 1. They have to maintain the speed limit > 2. All acceleration must be done by cruise control > 3. No drafting > 4. Windows up, A/C must be exactly the same in both cars > > The Test > > After 300 miles there didn’t appear to be much difference in the gas consumed, but after 500 miles Adam (tailgate down) ran out of gas. Jamie made it another 30 miles before he ran out of gas. This result was the exact opposite of the myth. > Water tunnel visualization > > According to the experts, a circular pillow of air forms behidn the cab of the truck when the tailgate is up. This “separated bubble”/“locked vortex flow” keep the faster moving air from contacting the truck, and thus reduces drag. With the tailgate down, the bubble breaks down and is no longer able to keep the fast moving air out, increasing drag. > > In their scale model with the water tunnel, they were able to see that the increased drag. With the tailgate down, the particles in the water were dropping down and hitting the tailgate. > > mythbusted ---
**Author:** ![N\_CTRL](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/n_ctrl/32/4982_2.png) [@N\_CTRL](https://forums.speedlife.net/u/N_CTRL)\ **Post date:** [October 20, 2006, 9:57am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/9 "2006-10-20T09:57:16Z")
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. ---
**Author:** ![MPD47](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/mpd47/32/7383_2.png) [@MPD47](https://forums.speedlife.net/u/MPD47)\ **Post date:** [October 20, 2006, 10:14am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/10 "2006-10-20T10:14:30Z")
> [@newman](#): > > EDIT: looking at the shape… the part you made may effectively ADD lift 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. ---
**Author:** ![Studderin](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/studderin/32/7197_2.png) [@Studderin](https://forums.speedlife.net/u/Studderin)\ **Post date:** [October 20, 2006, 12:19pm UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/11 "2006-10-20T12:19:05Z")
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 ---
**Author:** ![Studderin](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/studderin/32/7197_2.png) [@Studderin](https://forums.speedlife.net/u/Studderin)\ **Post date:** [October 20, 2006, 12:25pm UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/12 "2006-10-20T12:25:59Z")
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](http://i2.photobucket.com/albums/y11/studderin/NOPI/IMG_1973.jpg) 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. ---
**Author:** ![Studderin](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/studderin/32/7197_2.png) [@Studderin](https://forums.speedlife.net/u/Studderin)\ **Post date:** [October 22, 2006, 9:28am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/13 "2006-10-22T09:28:49Z")
These were a big PITA to do. But came out really nice 1st try:) ![http://i2.photobucket.com/albums/y11/studderin/IMG_2977.jpg](http://i2.photobucket.com/albums/y11/studderin/IMG_2977.jpg) 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. ---
**Author:** ![ImportMuscle](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/importmuscle/32/7615_2.png) [@ImportMuscle](https://forums.speedlife.net/u/ImportMuscle)\ **Post date:** [October 22, 2006, 10:05am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/14 "2006-10-22T10:05:56Z")
> [@newman](#): > > yes, but it also creates a quiet zone for air flow… > > Example: Pickup trucks get better gas mileage with the tailgate up. :word: ---
**Author:** ![VANDIT](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/vandit/32/4977_2.png) [@VANDIT](https://forums.speedlife.net/u/VANDIT)\ **Post date:** [October 22, 2006, 10:59am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/15 "2006-10-22T10:59:01Z")
> [@newman](#): > > yes, but it also creates a quiet zone for air flow… > > Example: Pickup trucks get better gas mileage with the tailgate up. :tup: to the diy and :tup: to Mythbusters.!!! i saw that one (trucks) ---
**Author:** ![Rx3](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/rx3/32/7194_2.png) [@Rx3](https://forums.speedlife.net/u/Rx3)\ **Post date:** [October 22, 2006, 3:05pm UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/16 "2006-10-22T15:05:59Z")
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”. ---
**Author:** ![Ninja](https://avatars.discourse-cdn.com/v4/letter/n/53a042/32.png) [@Ninja](https://forums.speedlife.net/u/Ninja)\ **Post date:** [October 24, 2006, 10:13am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/17 "2006-10-24T10:13:49Z")
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… ---
**Author:** ![brent\_strong](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/brent_strong/32/7203_2.png) [@brent\_strong](https://forums.speedlife.net/u/brent_strong)\ **Post date:** [October 24, 2006, 11:11am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/18 "2006-10-24T11:11:39Z")
> **[Chaparral Cars](https://en.wikipedia.org/wiki/Chaparral_(car))** > > Chaparral Cars was a pioneering American automobile racing team and race car developer that engineered, built, and raced cars from 1963 through 1970. Founded in 1962 by American Formula One racers Hap Sharp and Jim Hall, it was named after the roadrunner, a fast-running ground cuckoo also known as a chaparral bird. Troutman and Barnes were builders of the original Chaparral race cars (later referred to as Chaparral 1). Jim Hall purchased two Chaparral 1s to race. When Hall and Sharp began build... ---
**Author:** ![MaximaSE98](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/maximase98/32/7600_2.png) [@MaximaSE98](https://forums.speedlife.net/u/MaximaSE98)\ **Post date:** [October 24, 2006, 11:49am UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/19 "2006-10-24T11:49:44Z")
> [@newman](#): > > they did it on mythbusters. > > EDIT: looking at the shape… the part you made may effectively ADD lift 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 ---
**Author:** ![Rx3](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/rx3/32/7194_2.png) [@Rx3](https://forums.speedlife.net/u/Rx3)\ **Post date:** [October 24, 2006, 5:34pm UTC](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056/20 "2006-10-24T17:34:17Z")
> [@Ninja](#): > > It was attempted and banned from F1, as im sure it is from every other form of racing. > > … Pretty much. when the Chaparell hit Can Am, people were throwing fits. [Next page](https://forums.speedlife.net/t/diy-rear-anti-airdam-top-speed-track-mod/19056.md?page=2)