i know that lots of car manufactures use trays to close off the bottom of their cars, making them more aerodynamic...and aparently giving them more downforce at speed (they put a lip at the end to create a vacume to pull the car to the road) do you think this process would be as simple as buying some sheet metal and attaching it to the frame at various places....or do you think there is a lot more to it than that?

 

I hate to burst your bubble but this is probably more trouble than it is worth. (assuming your talking about a 1st gen) provided that your front valence and undertray is in place you will probably not notice much of a difference by adding a full undertray. The main battle as I understand it anyway is going to be covering the axle area (which is next to impossible on a solid axle, fendered car).

However if you wanna do some more research there is a very good book called Competition car downforce (I think this is the right title.) I have not read this book as of yet but a friend of mine has and said it was very explaitory or some pretty compex concepts.

The biggest improvement in my opinion is making sure the stock areo work on the front of the car is in good shape. This will help alot. You can PM Nick-7 or I'll get him to post here he's the one that read the book.

 

make it go to the back axle will help keep rust down, if nothing esle

 

Good qustion leif ...
You speak of high end cars like the Nissan Skyline GT-R and Ferraris..
While flat bottoming a first gen may be entirely unnecessary, there are areas underneath every car that requires any form of air foil, spoiler or wing to have the proper rake angles and such to be effective or they can actually become more of a detriment to the cars' performance aerodynamically as well as contain exhaust heat... only true way of determining that is by wind tunnel testing, or actually feeling your cars top end and acceleration speed reduce plus any instability provided you are very in tune with your car.
I felt a nice improvement at freeway speeds by simply adding a front airdam .. a later project will be making an air splitter/flat bottom til the front cross member with integral cooling ducts and possibly some form of rear diffuser as well.

 

Wow RacerX7fb that sounds industrious...

Don't FCs have somthing like that?

Allows the car to handel better at high speeds.

I could be wrong...

 

I do know what my car feels like at speed, and it feels very very shaky at top end, plus i do a little off roading (i spend most summers on logging roads and the temptation is too sweet to pass up) and i have had to replace my oil pan a few times and im running out of spares.

My goal is to add aerodynamic stability at speed, zero to sixty in our kind of cars is dependant on HP untill you get to trying to shave tenths of a second off, at the limmit of my first gen, which lies somewhere around 130mph, there is a floating feeling. i have read enough books on racing design to know how an undertray works, and i think it would work well...think about it...all of the air going thru your RAD hits the firewall causing turbulance, then it runs under the car cuz it cant exit out the hood, plus ait going under your car is stirred up considerably by the un even surface that is your underbody, i have always felt this is one of the biggest aerodynamic flaws of the RX-7...

I think im going to do it,,,just to see hwta happens.

 

oh i should have mentined that a rad deflector ala daytona cobra, Porsche GT2 and others would be required to prevent turbulance

 

So you are wanting to make a radiator deflector that would exit the top of the hood, and then try and cover as many of the underbody crevices as possible.
This sounds like a good idea to me. I have thrown around the idea about the deflector (mainly to get the hot air out of the engine bay).

I don't know if you want to worry too much about arodynamics if you take your car off road often. I think a decent sized rock could destroy whatever kind of under body sheet metal you might fabricate.

 

i aways wanted to do this like in this pic but aluminum to be cheaper on my car but i would it think that there will be poeple taht will think im a ricer

 

Underbodies do work, provided you build one correctly. There are several approaches, including a solid flat bottom and giving the car a rake (nose down, back up) which will provide a little downforce.

The trick is getting it to exert the same force on the front and rear wheels so the car doesn't feel spooky at high speeds. Good approach is using a two part underbody with seperate front and rear diffusers, the front being vented out the side or top of the car or channeled all the way to the back. Here's a cheap test, if you can aquire the equipment:

Mount a decent grade "laser tape measure" to the front and back of you car in a place you can see them (or more importaintly, your friend in the passenger seat can see them; watch the road when you're shooting down the highway at 80). Give yourself a set spead (like 80mph) to use for both tests.

Run without the underbody, and with. Take both measurements. You should see a smaller distance with the underbody; this corrosponds to your shocks being compressed from the extra "weight" of the air pressure.

If you know enough about your shocks, or perhaps can just get some people together to sit on your car and acheive the same measurements, you can calculate the downforce you added (keep in mind you should have more at speed than at a standstill).

If you have coilovers or something try the test at a few ride heights; you should see some very interesting numbers.

 

oh, and for construction materials: try foam-core board (very cheap) and fiberglass/polyester resin (not exactly expensive either). Since you're working in mostly flat shapes (except maybe the diffuser) it won't be hard, nor will it weigh much.