attention super zip tie mcguivers: underbody aero on the cheap?

[tastyratz]

ok guys so I want to impliment some underbody aero on my car. id like to have a large diffusers up front and I have a gp sports g4 kit on my car, I want to integrate a rear underbody diffuser to make the bumper a transitional advantage not an ass end parachute. I believe underbody aero is very important and I would prefer not to get a giant wing if I dont need it. I see that import fan has a carbon fiber universal diffuser for the front end for 200$ but wtf, I dont need a stupid huge ricer panel that will crack in the winter. my front end has the stock sohc bumper (slightly modified ;-) with the sohc lip and I wanted to integrate it into that.
rear doesnt have to be something terribly flexible but this is an all year round car and I dont scrape the sides or rear, but I do tend to scrape the front going into some peoples driveways. I dont wanna crack this first try.

key is something I can use thats relatively stiff but hopefully slightly flexible, doesnt look like complete ass, and will be able to resist a mild impact at the minimum. I have looked at getting sheets of aluminum and abs plastic but its still gonna cost me an assload for a piece that big. this is the cheapest car community in the world, does anyone have any creative ideas on how to achieve my goal on the cheap?

[drftwerks]

"this is the cheapest car community in the world"


haha thats so true

really cheap???

cardboard. haha,

how bout plywood, seen actual roadracers use it for front splittes

[WongFeiHung]

And exactly what is your goal for this "underbody aero"? Don't expect importfan products and homemade diffusers and panels to provide any real downforce without some engineering knowhow...

[FaLKoN240]

Damn dude, I can't even read the whole post, your lack of paragraphs, and good sentence structure hurt my head.

From what I read, I think you should get some of that Home Depot garden surrounding plastic stuff, it's cheap and durable, since you're soo worried about it cracking/breaking.

[shortandsour]

around here at metal depot you can get a piece of .135 alumnium thats about 50 x 35 for around 20 bucks, thats pretty cheap if you ask me. also you can find pretty decent size alumnium sheets oh ebay.

[g2ic02]

i made one for my front(splash guard) out of an aluminum sheet i got from the local hardware store.

[tastyratz]

damn man i wish i could find aluminum sheet that cheap lol. wongfei: what im trying to achieve is actually suction and vacuum. underbody aero is more important to high speed grip and stability than a wing will achieve if done properly. you dont need an engineering degree you need an 8th grade education. i would be making the underbody of my car flat to keep undercar air velocities up. also will be putting in splitters to make it laminar for increased suction and stability. theres a science to this.... im just broke lol

[someguy_240]

1/4" plywood is flexible, pretty light and itll work.

but it wont look pretty and it might sag a bit if you dont fasten it properly.. whtvr and damn that rain will mess it up but whtvr if you want to experiment wid it why not?

[chmercer]

i made an undertray for my front bumper out of some aluminum. i got a 4' x 10' piece for i think like 70 bucks? so i have a shit ton leftover. i traced the edge of the bumper onto the metal and cut it out, then rivited it onto the bumper to where about 2.5" inches was exposed at the center. riveted it on all the way around, and cut it off flat at the back edge of the bumper. riveted some 1/4" hollow aluminum 3 sided box stuff along the back edge and down the middle (in a T shape) to keep it from sagging and to give it some rigidity. i didnt weigh it; its probably heavier than it needs to be, but i made it more to keep my dying fiberglass bumper in one piece than anything else. i resined carbon fiber cloth onto the exposed edge of it, for a touch of rice.

and it would help with aerodynamics if my car was actually low, but im having wheel clearance issues so the car has like 3" of ground clearance on the front. kindof bites

[kandyflip445]

SPL has a universal plastic diffuser but they don't list a price.

I found this site looking for some plastics. http://www.sourceplastics.com/

Through that site I found this. http://www.misterart.com/store/view.cfm?store=001&group_id=8049
It's corrugated plastic cardboard. You would most likely have to find a ways to fill the inside or you could just seal the edges with something like epoxy or silicone or some kind of other plastic. You could stick little metal dowels (maybe some welding rod) inside the holes along some certain places to make it less flexible at speed. Or to make a more solid mounting point. Like:

"| |" = 1 space
"|o|" = 1 space with a rod

|o| |o|

Inbetween those you could perforate the board and put washers on the top and bottom to give it a little more strength.

That's all I can muster up right now.

[that180guy]

"this is the cheapest car community in the world"


haha thats so true

really cheap???

cardboard. haha,

how bout plywood, seen actual roadracers use it for front splittes

lol, i have this options vid, and this one jdm silvia guy actually has cardboard as aero

[chmercer]

SPL has a universal plastic diffuser but they don't list a price.

I found this site looking for some plastics. http://www.sourceplastics.com/

Through that site I found this. http://www.misterart.com/store/view.cfm?store=001&group_id=8049
It's corrugated plastic cardboard. You would most likely have to find a ways to fill the inside or you could just seal the edges with something like epoxy or silicone or some kind of other plastic. You could stick little metal dowels (maybe some welding rod) inside the holes along some certain places to make it less flexible at speed. Or to make a more solid mounting point. Like:

"| |" = 1 space
"|o|" = 1 space with a rod

|o| |o|

Inbetween those you could perforate the board and put washers on the top and bottom to give it a little more strength.

That's all I can muster up right now.

woah, that seems :ugh: but for some reason i kindof want to try it. would be hella lightweighter than aluminum, and i think they already use somthing like that anyway.

reference
http://img316.imageshack.us/img316/7703/jgtcsofronastouringcar3dq.th.jpg (http://img316.imageshack.us/my.php?image=jgtcsofronastouringcar3dq.jpg)

[kandyflip445]

Hey, it's cheap. lol

It may be worth the time though. I dunno. I like my stock body. ;)

[drftwerks]

lol, i have this options vid, and this one jdm silvia guy actually has cardboard as aero

haha i have that one. teh yellow and black silvia

[tastyratz]

that doluck piece on raretricks website is 475 :-/ i doubt its much cheaper on spl. that corrugated plastic seems like a winning bet however and im thinking i might go with that. that was an excellent suggestion man. originally i was considering the possibilities of using like a foam posterboard and spray truck bedliner to seal it. when you have a low car something like that could work well and be disposable incase something happened. more than likely im going to try to research more into getting that board locally or in wider pieces. im going to have to measure my bumpers to see how wide it is but 48 inches seems just a little short in concept...

edit: just looked at that site again and seen they had sheets 48x96 :rawk:

[drftwerks]

Tap Plastics

[docrice]

do you really think that this will be effective??? Seriously, do you know how fast you have to be going for these kinds of effects to take place? I dont know what kind of 240 you have, but these kinds of aerodynamic effects aren't really gonna be noticable until close to max speed. Someone please correct me if i'm wrong, but i don't really think this will help you much if at all...

[kandyflip445]

Shit. If it doesn't help it's not like it cost much. lol

[chmercer]

do you really think that this will be effective??? Seriously, do you know how fast you have to be going for these kinds of effects to take place? I dont know what kind of 240 you have, but these kinds of aerodynamic effects aren't really gonna be noticable until close to max speed. Someone please correct me if i'm wrong, but i don't really think this will help you much if at all...

aerodynamics come into play largley around highway speeds, reference expensive cars with automatic wings. they pop up at like 60, not 150. obviously some will be less effective than others and require higher speed to become noticable, ie dive plates aka canards.

[tastyratz]

yes im aware, i can feel a significant drag on my car around 50mph and up since i put the g4 kit on my car. its just a big rear parachute. ive messed with this stuff before and it really does make a difference. daily driving is 85mph for me and you feel this sorta stuff at that speed... aero comes into play ALOT. if underbody aero is known to have a larger impact that a properly designed wing.... and you can feel a wing at 50-60mph speeds.... how much of an effect will this have?
every little modification ive made to my car aero wise was practical and noticed. the bumper will be great in the back when its not a big parachute. side skirts are little known but one of the most important aero mods you can have. air escaping out the side is not air contributing to the vacuum. i plan on building onto my side skirts to make them even more aerodynamically efficient. im looking to tune my car practically, and if i can pull this off under a hundred bucks entirely then ill be happy.


http://www2.mech.kth.se/courses/5C1211/KTH2Total.pdf
look at page 15. notice the yellow under the car? thats because a low pressure zone creating a velocity will increase high speed velocities. when my cars finished and built properly i plan on taking it 140+mph, but only when prepared and everything fully addressed

[kandyflip445]

Lexus and other car manufacturers are using underbody aerodynamics to increase gas mileage and ride quality at highway speeds. I remember seeing a Lexus commercial showing them using dimpled underbody covers. I'm thinking they're using this to increase the surface area under the car helping to keep the speed of air up. Like a wing the air going over the car has to travel a farther distance so the air has to travel at a higher speed. This creates a lift on the car. If you can keep the airflow under the car smooth and as long as you can make it then it will help reduce the lift on the car.

Or at least that's how I see it as. But I don't have any kind of degree. Just some reading here and there.

[docrice]

what i'm saying is, how bad is the undercar aerodynamics of a stock 240? hell it might be as good as the lexus (not likely), maybe this underbody aero isn't even necessary. Just wasnt sure how much research you did on the car's aerodynamics...

[CaoBoY]

so you have a stock front end AND a body kit on your car? huh? and also i believe you said this was a daily driver? whats the point of this? your car is not a race car, you dont need that much underbody aero that will probably get stuck on a speed bump or something. i dont really see a point in this, and its more rice to make this if you ask me.....

[matlock]

All I know is that it is MacGyver, and that the "Plastic Cardboard" is called Coroplast and it is really flimsy and likes to bend in the wind...I work for a graphic design/sign company and we use it a lot and it is not the best stuff in the world not rigid at all.

[kandyflip445]

That's why I said you could stick some metal rod in the spaces to make it rigid.

Also, why do some of you want to be so negative and go so far as to say it's rice? He is making an attempt to better his car and is just looking for some help. So what if he doesn't have 1 billion dollars. If it works I bet other people will follow in doing what he will.

[chmercer]

does anyone know if they sell sheets of fiberglass that are already resined? just like a big sheet of rigid fiberglass?

[tastyratz]

i dont think working on a part of your car to have better functionality where nobody can see it is rice. rice is apc led shift knobs and giant plates of chrome in random places on the car. rice is not smoothing the underbody of your car to increase efficiency at high speeds. why be so negative about this? its my own choice to want to do something to better improve my car WITHOUT adding a big ricey wing. if possible id like to remain wingless. my car isnt a nascar but i still do mods to make it as close as possible to something like that and just about everyone else on this board does it too.

anyways. I have 0 offset wheels and I had to chop of the front half of my wheel well liners. I also have the holes in the front bumper messed up so I had nothing to attach the underbody splash guard to. if I look under the front of my car its aero hell right now and I want to do something to change and improve that. the center of the car isnt too too bad but I also have the large high pressure zone in the back with the rear bumper (now being a parachute) the aero back there had room for improvement even with the stock bumper but now if I dont do something it will be worse.

plans are attaching a sheet to that rear bumper working around the exhaust and running it up to and a little past the diff or so. I plan on running a big sheet in the front as well to remedy most of what ive mentioned previously. ill also have to build around a massive hybrid intercooler, intercooler piping and brake air ducts. the way ive modified my front bumper looks like this guys car: http://forums.vwvortex.com/zerothread?id=1516760
http://www.we-todd-did-racing.com/wetoddimage.wtdr/i=wNDk4NDMyNnM0MTNkZmQzMXk1NDE%3D

[krustindumm]

http://www.honda-tech.com/zerothread?id=1147311
The splitter is alumilite [1/8" sheet of plastic/nylon sandwiched between two 1/16" sheets of aluminum] Punched holes in the notched tabs on the spoiler and then punched the holes accordingly on the splitter....bolted together with a stainless steel button-head allen bolt.

The splitter protrudes out 1/2" in the front and approx. 1" at the corners, much more than that and it would create too much downforce....at 90mph on a Del Sol with 1,250 lb. springs on the front it was bottoming out the suspension with a 1.5" lip...I'm only running 500+lb springs on my integra so I'd rather play it safe

http://www.speedminded.com/images/integra/bumper/dsc05364_sm.jpg

[kandyflip445]

^That's cool.

[aa87]

haha i have that one. teh yellow and black silvia

With the cardboard trunk!

[Rennen]

I want to integrate a rear underbody diffuser to make the bumper a transitional advantage not an ass end parachute.....


....you dont need an engineering degree you need an 8th grade education. i would be making the underbody of my car flat to keep undercar air velocities up. also will be putting in splitters to make it laminar for increased suction and stability...


Obviously an engineering degree would help you out in this case.... the rear bumper isn't a large parachute... read this (http://www.zilvia.net/f/showthread.php?t=68044)


First question: Is this an all out race car? what racing organization, what ruleset? If it is not a racecar, just stop now.

If you are running this plywood terror on the street, You will need to make clearance room for the suspension arms, diff and driveshaft, and exhaust...... then you are left with? Nothing that really creates drag!

Real diffusers are made with months of wind tunnel testing because the most important function of a diffuser is not to be flat, but to manage the airflow, and match the velocity on exit. If you were miraculously able to speed up the air beneath your car to noticeably affect downforce you will have fuckingfast air meeting up with slow turbulent air behind the car, creating more turbulence, and more drag. So this very tiny percentage increase in downforce you see will be completely negated by drag and weight.

What I am trying to say is: If you want a neat project to occupy your time, go for it... but just don't think you are making your car better/faster


-Matt

[CaoBoY]

^^^ EXACTLY what i was saying. If this isnt a race car, theres no real point of doing it. you are not going to be going fast enough ALL the time to make this even 40% useful, unless you live in FnF usa, i dunno what ur real point of doing this is, unless you think its cool and you think it will make THAT much of a difference. It'll probably end up weighing more and slowing the car down more than the supposed drag you are getting. Whatever though its your car, and if you want to endup stuck on a speed bump because your cool ass 'diffuser' got stuck, so be it. :ghey:

[MakotoS13]

it is feasible to say that this could dramatically aid in terms of high speed STABILITY and maybe 120mph+ actual speed. once you get above like 120 or so you're fighting wind for the most part.

the fastback is a very sleek design but its undercarriage has holes. the rear bumper (for example) is a major thing just like most cars not designed to be fuggin supercars. why do you think C5's and C6's have those little vents in the back? it decreases pressure by increasing flow. why do they make rear diffusers? cause it helps transition the air smoother thus increasing velocity THUS decreasing drag which helps stabalize the car AND free up horsepower at higher speeds.

[SochBAT]

+1 Makoto

And it looks cool. Don't bash his balls for trying his own thing. Everyone is a sentient being, all have our own ways of doing things. Keep it up!!! And tell us how it turns out with pictures!

[CaoBoY]

if it works, so be it. if you are doing it purely for asthetics, then go buy one already made. if you are doing it for asthetics and being cheap, its probably not going to look good....if you are doing it because its going to be ur weekend track car, not AUTOX (where your not going to generate enough speed anyways) then i see a point in it. if you just daily drive ur car around town, and a little on the high way, i dont understand why you want to do it unless its for asthetics...which like i said before, go with an already made appliacation, which will look good also...im not trying to hate, just more as looking out for you.

[chmercer]

^^

bullshit. aerodynamics have been proven time and time again to have large effects at low speed. a stock sti runs reasonably faster than an sti with the wing removed on the same autocross course.

[drftwerks]

how aerodynamic is that bumper with a big front mount?

[CaoBoY]

^^

bullshit. aerodynamics have been proven time and time again to have large effects at low speed. a stock sti runs reasonably faster than an sti with the wing removed on the same autocross course.

thats a WING not an underbody diffuser.. its a little different...how many stock sports cars ( that are geared for the middle class consumers) have full underbody defusers?

[TurDz]

I think it's a fun project, but you have to be realistic. Maybe look at the latest gen Altima, and the Altima SE-R, and look at what kind of aero they added and study it. The simple aero kit actually reduced drag from 0.33 to 0.31 according to GRM, which IMO is a very good improvement.

The basic things to check first is stuff like the underbody rigid plastic panels, like the ones under your engine bay. Check if they're all intact.

What you're aiming for is a very smooth flowing underbody without things that will increase pressure. With smooth flow, you can increase air velocity underneath, and if the rear diffuser is correctly designed, it can transition nicely at the end of the car.

just don't expect many universal or ricey fiberglass covered CF parts to work well.

[spdfreek0o]

IT WONT WORK!!!! :rofl:

[Rennen]

It irks me when people think "oh, I saw this on a supercar, it must work if I do it on my POS." I don't think anyone knows how much testing and computer simulation goes into creating a part like this. Unless you have a quantitative way of testing (like comparing lap times) just stay away from wings and diffusers, they'll do more harm than good.

Just for shits and giggles... go fill up your sink with water. Turn on the faucet on low. Notice that the water isn't disturbed much? Now crank your water up to high, see how much turbulence is in the water? If you were able to increase the speed(which you won't) this is what will happen behind your car, since you have no way of matching the airflow. And the size of the turbulent vortices creates the force of drag... you will make more turbulence, and more drag, while increasing weight. This is not something I'd want to do to my car.

Your time would be far better spent just keeping air out from under the car by lowering it or creating an airdam/sideskirts.

-Matt

[tastyratz]

This is a daily driver that sees highway time all the time. Its not an all out race car but I dont drive slow, and I also plan on building this for very high speed racing. An underbody diffuser may not make as much of a difference if its not tested in a wind tunnel, but smoothing out areas in the underbody that may be high pressure zones with flat panels will obviously help regardless of the "perfect angles". I may not have the perfect exit radius on splitters I put in the rear but it will keep flow laminar, reduce turbulance, and increase stability (think in terms of a keel on a boat). The stock bumper is not so much a big parachute but the gp sports g4 bumper is if you seen it. I want to remedy this situation and keep this bumper.

"Speed holes" in the bumper before anyone suggests them actually create more drag by allowing more turbulant air to pass through that excuse to put more chrome on in your bumper. The high pressure zone in the bumper allows air to pass underneath and around.

That integra post was excellent and a prime example of my goal. The purpose to my post was not to argue my concept with people who think this is trivial and are entitled to their opinion. The purpose was for advice and ideas not discouragement and insult. If you have positive input, please enlighten me.

[MakotoS13]

It irks me when people think "oh, I saw this on a supercar, it must work if I do it on my POS." I don't think anyone knows how much testing and computer simulation goes into creating a part like this. Unless you have a quantitative way of testing (like comparing lap times) just stay away from wings and diffusers, they'll do more harm than good.

Just for shits and giggles... go fill up your sink with water. Turn on the faucet on low. Notice that the water isn't disturbed much? Now crank your water up to high, see how much turbulence is in the water? If you were able to increase the speed(which you won't) this is what will happen behind your car, since you have no way of matching the airflow. And the size of the turbulent vortices creates the force of drag... you will make more turbulence, and more drag, while increasing weight. This is not something I'd want to do to my car.

Your time would be far better spent just keeping air out from under the car by lowering it or creating an airdam/sideskirts.

-Matt

this is not an opinion. this is fact: you are wrong. your sink analogy does not work because it is using the SAME shape of the drain and sink while increasing velocity of incoming water. of COURSE there will be increased turbulence.

this is how you make your analogy work:

instead of a sink you make a funnel and smooth out all the transition points. then even with your increased flow there is smoother flow.

take a look at the rear bumper. notice the overhang. anybody that thinks eliminating that drag will not help doesn't know dick about cars or aerodynamics.

you dont need a wind tunnel to eliminate obvious drag eliments.

so if you can't keep up get the hell out, kiddies.

[Rennen]

take a look at the rear bumper. notice the overhang. anybody that thinks eliminating that drag will not help doesn't know dick about cars or aerodynamics.

so if you can't keep up get the hell out, kiddies.

The rear bumper holds laminar flow for longer, decreases flow separation, creates smaller vortices, less turbulence, and less pressure drag on the car.... but then again, I don't know dick about aerodynamics or cars at all :squint:


You aren't seeing the big picture with the faucet example. The sink represents the pocket of air behind the car, the stream of water: air exiting the bottom of the car. If this flow is too fast (or too slow) it ends up disrupting the air behind the car. This disruption causes larger vortices of turbulence and more pressure drag on the car. That is why halfassing a diffuser will do more harm than good.


tastyratz: A front splitter like that on the Integra will help keep turbulence down over engine parts and the TC brackets ( I just helped make one for an ITA 240SX last weekend) Just make sure to leave enough room for hot air to escape the engine bay. Otherwise the rest of the underbody is more or less smooth, or moving parts on a street car. The only glaringly obvious aerodynamic problem you seem to have is this aftermarket rear bumper with a stock front bumper... any particular reason you need the rear? You would see far better aerodynamic gains elsewhere, rather than adding weight to the bottom of your car to bandaid fix a mismatched bumper.

-Matt