I was reading an article in the paper today about the new porsche carerra GT. It has a carbon fiber undertray, much like that on an indy car to help with downforce. Would it be possible to make one for a 2GNT? It most likely wouldn't be carbon fiber, but would it even be worthwile? Our cars can reach some pretty high speeds, and it would be helpful for somebody who wanted to race their car on a road course. I don't plan on making one anytime soon, but I just wanted some more info. How exactly do they create downforce?

They create downforce using this aerodynamic principle:
If the air moving UNDER the car moves faster than the air above it, it creates a pressure difference resulting in the car being pulled downwards. Same idea behind airplane wings. When air goes over a surface faster than it goes under, it creates lift.

When you lower your car, you increase the velocity of the air flowing underneath it. A tray smooths the underside of the car, further increasing velocity.
I hope this post of mine is intelligent enough to be in the advanced tuing section. I've always thought a tray would be awesome.

especially if our cars flew

Yup good explanation. Ferrari has been doing that for years on their latests cars. One even incorporated fan I believe for the engine ocmpartment sectio to draw air up, reducing lift.



15.9 @ 86.7mph

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Under car trays have been used for decades and only recently have really seen duty on street cars. Rally cars also use them to protect the underside. The biggest issue with an undertray is trapping heat and servicing. If you want to make a cheap one, go to home depot and buy some thin type of sheetmetal and have it fabricated. I considered doing this years ago and worked out the schematics once but then never got around to it. You have to be sure to address the ventilation issue.

I'm thinking that if you ran two main panels longitudinally alongside the main exhaust line, you could bypass most of the cooling issues while still providing an increase in aerodynamics. You would want to leave an access panel for the beautifully placed fuel filter or your aux pump if so equipped, but would you do anything regarding the suspension arms? Curious... :P

Lexus had a neat idea on the suspension arms... They gave them an aerodynamic shape to them, kinda like knife edging them. I bet that someone with a tig welder could make some pieces and weld them into place that would be a bit more aerodynamic...
-=B-=

I imagine if you got enough airflow across the suspension arms, you could make them into little wings to put the downforce right where you really need it - at the wheels. I think the airflow in the wheel wells is probably too turbulent to make it work. Someone needs to make an open wheel DSM. That would be cool, imo... :P

I actually have been thinking about this a lot lately and I have posted on a few other sites. dsmtalk.com and machvforums both have a post on this and some very good insight and knowledge on how it works. Also, there are some pictures of real cars that have these on them. what you basically need is

1) up front, basically just a flat piece under the front part of the the car, back to aorund the wheels, maybe a little farther.
2) at the back of the car you need a diffuser so the air can expand out the back and help smooth the airflow.

as you smooth the airflow under the car, the air will move faster and help create a lower pressure underneath the car and this will sort of pull the car to the ground.

Right now im in the process of trying to find somewhere to buy material for it. I was just thinking of using some sheetmetal but i cant find it anywhere. if i find something better ill use it.

Now if you put a piece under the front bumper, you now have blocked off the area jsut below your engine so you know how to worry about cooling issues. WELL, depending how it is made, you can have the piece only go to the middle part of the front wheels so there is still an opening in the back, and you coudl also, remove the weatherstripping at the back of the hood and then maybe add a washer or too to the bolts that hold the hood on. This would raise the hood in the rear slightly and it would leave a nice opening at the back fro the hot air to rise up and out of. im not sure how important the weaterhstripping is but i am thinking about doing this.

so, as soon as i find a good material that i want to use i will be goign to work on this. it would be nice if i could get a somewhat high powered fan and a smoke machine because i could blow the smoke underneath the car and see what the air does before and after the pieces are installed. also it would help with what areas are more turbulent

Check out www.mcmaster.com

You can buy sheets of steel, aluminum, plastic, and composites.

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

thanks for that site. helps moocho

Great idea.

Just one problem...
Removing the weatherstripping and spacing the back of the hood will let NOTHING out of the engine bay. That is a high pressure area. That's why cowl induction works, and why the inlet for the climate control is up there. Cool air might be forced into the engine bay, but for removal of the air from inside of the engine bay, you need an extracto.

An extracter is a vent in a low pressure area of the hood. Wherever the air accelerates is a good place. Usually, though, it is just easier to put a hole behind a bump (insert appropriate inappropriate joke here). The bump pushes the air in another vector, away from the hood, creating a low pressure area. The hole is where the replacement air for the displaced air comes from. In the right place, an extractor duct can keep almost anything cool. Hell, It might even make me cool.
-=B-=

http://www.machvforums.com/showthread.php?s=&threadid=20732&perpage=15&pagenumber=3

go there. that is what im thinking about doing to my car. now from the looks of it the front piece does no go very far back. Im thinking that if it does not go real far back that air and heat would still be able to get out of the engine.