Shookum2004

I'm not sure if this is the correct umm forum.

After poking around on the internet, i came across cars that have flat underbody. Decreasing air drag or resistance or something.

HOwever, not many places have i heard much about it. Alot of high performance cars use it.

How hard would it be to have some type of sheet metal...at least smooth. Or as closely flat as possible.

And what type of gains would be possible with such a setup?

The concept makes sense, but i guess it was a modification worth doing, the whole world would be doing....input please?

//<86TA>\\

iTrader: (15)

i dont think doing that would make any noticable difference at all for a street car, maybe if the things runs at 200 mph all day it migh help but i dont think you will prove anything. if you want the car to go faster drop in a v8

Shookum2004

Lol lets not bash my v6. I now have a v8 trans am also ...so my engine is not the issue. Its the aerodynamics or drag or w/e that is the issue. I mean air coming from the bottom of the car has to go up into other parts of the car. And plus some new SUV taht is super aerodynamic has a flat underbody. And if its good enuff for a Sports Car, good enough for me. Plus it would not weight that much...

DFENS

If you were runnin an Elise or Ferrarri, maybe a Z06 Vette, I'd say go for it. If you just want to do it, go for it. But it won't do too much IMO. I'd say that the SUV has it more for offroading than aerodynamics. If you were to raise the 'maro and go offroading, go for it.

Think of a brick. It's about how the car looks. Now, throw it as far as you can. Now, smooth out one side of the brick, throw it with the same force. Chances are that it'll just go the same distance.

Sonix

iTrader: (1)

if you welded on a flat piece below, such to smooth it out, that'd probably work. I'm thinking you'd want to remove the "crinkled" material above it. The crinkles add strength, so that might not be a good idea. Also, those grooves that run front to back, probably help streamline the air, and make the car slightly more stable. At speeds upwards of 150MPH maybe.
Also, consider your air damn, and how it functions, while you're brainstorming this.
I think the jazz under the car would effect things most, like exhaust, tranny, cross members, etc. I you could streamline or avoid some of those, you'd probably see more aerodynamic gains, then by simply smoothing out the underbody.
I do however always like to see more info about these innovations, so if you come up with some more info on this subject, do post. Like links to other webpages or threads where people have done this mod to an older car or something. (ie, not on a brand new car, 'cuz you can't ask the engineer at porsche why he put it on the SUV or whatever...)

wiseman9986

iTrader: (2)

you wouldnt want to weld any panels on that would just make problems and moisture would get trapped between and could leat to rust but making it all out of aluminum sheet and using those body screws like ppl use to hold on hoods and other body parts and that way you wouldnt lose acces to anything

vorgath

The idea of completely flat underneath hmmmm I'm sure it was before but first time I myself saw it was in a Ferrari from the '80's.


If you want some really kewl ideas, do a search for those Camaro pics from Japan, the airdam assembly is something else.

87CIZ

iTrader: (8)

i always thought that would be an awesome idea for a car if you take it to the salt flats. As far as a street car it wouldnt help you'd end up adding more weight. not to mention having to try and do something with the exhaust. It would help though when the wind is blowing really hard i can feel it hitting the firewall with my feet when it gusts.

Comp788

If you look at a nascar most of them just use an air dam and side skirts to divert the air around the body. The Ferrari and Lambo have the air go under the body and then have ground effects (undercar wing) at the back of the car under the engine. It acts like a wing would if it was attached at the back of the body. Since the engineers are looking for streamline body styling they use the ground effects to acomplish the same thing.

I think that Sonix is right that you could improve some of the undercar things and gain more then just putting a skin under the body. Lets face it some things look great on the idea board but there is also the real world.

Shookum2004

Just an idea. I mean it would of course be boltable and easily removed. From a drag racing standpoint if anything...an extra 5 lbs of metal on the car for a full 5 minutes. Shouldn't mess anything up. Plus i see, even if minusculey it helping more than hurting. But it was just an idea...

sofakingdom

iTrader: (1)

On a 6-cyl car, I'm about positive the extra weight would slow it down more than any reduction in drag would help. Even if it was only 5 ounces, let alone 5 pounds.

BMmonteSS

You might want to consider that if you put a complete underbody tray on the car it would over heat in about 2 seconds. Camaro's are bottom feeders, they get their air from underneath infront of the air dam that hangs down and then spits it back out on the back side of said air dam.

You may want to consider just doing a front splitter. This is just a lip that extends out form the bottom of the front spoiler about 3 or 4 inches and then would extend back 18" to 24".

You might try searching around on corner-carvers.com there are several threads on the subject, and the consensus is that above 100 mph it adds an apreciable amount of downforce.....well technically it removes lift.

FSTFBDY

iTrader: (33)

Here are some good Pic's that will help you get the idea of the above idea ...

87CIZ

iTrader: (8)

those are awesome looks like the small vents are for brake cooling ducting? Hard to tell but would be an awesome idea if not. It lets all the air the radiator needs to keep it cool, and doesn't close off the back and lets the air escape. For those of us running a cowl or a hood that isn't sealed at the rear like my RAII hood air comes in from bottom exits at top.

Red Devil

Vader used to have a pic of the skirt he has on his car.

The downside to the underbody stuff is you also need to understand the aerodynamics enough to know where and how much to divert as you could cause some seriously dangerous conditions at speed if done improperly. The skirt is much safer, lighter and a better choice for most vehicles on the road.

turbochargedrs

headlight covers are going to do more for aerodynamics than covering the underside of the car and if you dont have them because you dont like the gay smoke effect they make clear ones.

BMmonteSS

The area at the base of the windshield is a high pressure area, which means that at high speed air is actually entering your engine bay in this area. You might actually reduce lift by rigging up some kind of seal between your hood and the body.

This is also why cowl induction hoods work, they use this high pressure area to force air into your carb. You'll also notice that this is where nascar gets it's air from.

scribbles

I was really into this bout 2 months ago. I found out a few things. One, third gens are Very aerodynamic, because of many factors, but one of the major factors being the angle of the windshield. 87-89 Trans am's are the best at speed because of the low, raked front bumper, and headlights. The front bumper makes crazy down force at 120+mph. the best drag reduction can be made under a car, but it won’t matter till you hit 160mph, get more air into the radiator through designing a better air dam. 2 lower the car, simple cheap, lowers the center of gravity, and reduces volume of are going under the car substantially. 3 get air out from under the hood. Only way I can figure out how to do this is a reverse cowl Very close to the back of the radiator so it is unaffected by the pressure wave created by the windshield. Remember the more air you get out of the engine compartment the less gets under the car. Next build an air splitter as explained above, also will create more down force, and limit the air under the car. Last build a air diffuser, it is a curved and ribbed plate under the rear of the car that acts like the feathers on a dart and helps the little air left under the car smoothly enter the stream of air coming over the car. If you cover the entire bottom of the car their would be way too much heat built up. But from what I have read, all these things will only matter at over 160, and all that will only affect the top speed by about 7-8 mph at almost 200, and you need 700hp and perfect gearing to get close to 200.

scribbles

Oh also forgot to add, the side windows will be sucked out of the car at round 175 by the vacuum of air going round the car caused by the windshield, not a problem in most cars but ours are not in a frame, and not reinforced to pull out, just pushing in, so either have someone duct tape them or figer out something for yourself.

pimpflea

I always thought they were for rally cars that had to skim over puddles of water, and stop dirt and crap clogging under the car?

Calorus

I'm not sure why so many are being a little ignorant, and very negative, it's actually a very good idea.

The whole point is that it creates a low pressure area beneath the car with means the the net pressure acting upon it is downwards, it's incredibly simple.

Contrary to claims made: a) Fairing in the headlights would not have any where near an equivalent effect. Once the Headlight is full of high pressure air from being pushed into atmospheric pressure air at high speed, it may as well be faired in.

Cars will tend to expel all air taken into them to their undersides, this creates a high pressure zone beneath the car which dissipates as the car rises, meaning that by definition, it creates instability. If the net force between the top side of the body with its higher pressure, long path length flow is greater than the underflow, the car generates more and more downforce with speed - in fact it should typically be FAR more efficient than a spoiler on the upper body, and has far less drag effect, resulting in a huge aero-efficiency boost.

rocluvr0013

My side windows pop out around 140

ishada

True, however the lotus elise has a 4 banger built by toyota. Also our cars are not shaped like bricks.

I would say take the car to a wind tunnel and smoke line it then do the same with smooth bottom. Chances are you would **** your pants to see how much an air tunnel costs. Otherwise all this is pure speculation.

gray89vert

iTrader: (3)

good visual description! lol
nice work so far on the underbody

Dewey316

I highly suggest you start doing some reading on aerodynamics, a good book to start with, is Competition Car Aerodynamics by Simon McBeath. It starts with a real basic overview and some begining fluids info, and then applies it car aero. The a large section on undertbody design, and rear diffuser desing, along with a great chapter on splitters.

It would be pretty easy to cause more harm, then you do good, but just trying to make something. Under car dynamics can get tricky, since the car is so close to the ground, even attached airflow can start to interact with the ground. Idealy you can use the undertray to create a venturi style effect to help speed up the undercar air. You will also have to do a lot of work, and testing, on the rear of the car, the way the air exits, really makes a big diffrence, if you stall the air up on exit, everything you do, is in vane.

scribbles

"My side windows pop out around 140"

Do they just pull out a little or really bad? I have been over 140, but not by much, and never noticed more than whistling. And I have read that you are ok with stock design until 170 -175 at that point they will be ripped out and you will have a problem, because or the uneven, extreme drag.

Dewey316

It has to do with the pressure diffence inside the cabin. Rember, high velocity over a surface = low pressure. So you have basicly non moving air inside the cabin, and very low pressure across the windows, they are going to want to suck outl.

rocluvr0013

You can visibly see a gap between the window and the seal.

Its mostly just a whistling noise however.

MaxxMitchell

iTrader: (4)

You looked at the window when you were doing 140+?

I think adding a skin of some lightweight material would possibly help, but at very high speeds. Those of witch the L98 has troubles hitting stock.

Fiberglass sheets, or carbonfiber comes to mind. You could make the fiberglass yourself, and it would be pretty light, and ridged, plus it would be easy to mold in the rear diffuser.

I think alot of this under car areo, is only going to effect if you are going for some top speed runs, and are trying to get out every MPH you can. For a car thats not going to see much over 130 in its lifetime I dont think you will notice anything, but you will gain experience, and want to tackle more worthwhile modifications in the future.

ZEEYAA

My windows were fine at 155, but I have good seals and you just set the adjuster to where when you close the door you have to roll the windows up into the seal. That even stoped the noise above 140+.

nelapse

iTrader: (17)

The sheet metal that would be required to do a sufficent job would weight around 30 or so lbs... instead of the whole body... why not create a rear diffuser? Drag will catch the rear skirt of the rear bumper. Fiber glass or use sheet metal to diffuse the drag. Most real diffusers are flat and have fins that go forward to back.

(when I mean fins look at a tpi plenum... looks like that)

Gumby

Check out Dodge avengers, They had a very well designed rear bumper diffuser. WHen they ran them in the IROC race, they were able to race bumper to bumper without the typical problems. How when they get close, they get sucked in and bump. But they oculd ride paint to paint with no side effects from the rear draft.