fLat bottomed (girls) make the race car go round!!!
 

Its begun. Time for a flat bottomed car and a rear diffusor.

So far the car has a front splitter that goes back about 4 feet covering where the old shield used to be. Now ive got another 2 feet about to go on with this template i made (just need matterial i wanna use). The rest of the way back should be pretty simple cutting out spots like where the exhuast flanges hang a little low and going out far past the side skirts for some side splitter action.
http://i39.photobucket.com/albums/e1...snzy0vbjj.jpeg

http://i39.photobucket.com/albums/e1...s9fcad9nl.jpeg


Now onto the rear diffusor. Im still not sure what to do but this is what i have so far. The diff cooler bracket i made to catch air under the car and force it up into the cooler has what seems to be a 15.2* up angle. A 458 i tested had a 17* up angle but ive also seen flat diffusors. Guess this is as good as its gonna get without a wind tunnel. Now on a rainy day on the highway a huge rooster tail can tell a lot about a diffusor. Im also not sure how many fins to use or if they should be straight or taper out like ive seen after the center 2 like this / | | \.

http://i39.photobucket.com/albums/e1...pscvn0cdqe.jpg

What i did since the car was up in the air, i ran a string from the front to the back touching points of the car. This insured the flat bottom will be flat and that the fins are parallel to the ground. So far ive made 2 fins that are 10" apart. I dont know if ill have 4, 6, or 8. These 2 are straight as a arrow.

Any thoughts from here????

http://i39.photobucket.com/albums/e1...solp9idtc.jpeg

http://i39.photobucket.com/albums/e1...siyezqnp5.jpeg

http://i39.photobucket.com/albums/e1...skaiy5o24.jpeg

http://i39.photobucket.com/albums/e1...shl4tfazo.jpeg

http://i39.photobucket.com/albums/e1...sxivjmojj.jpeg

Awesome!!

God damn, what angle is the diffuser?

15.2 like I said. Also the 458 is 17* so...

Yea but the 458 doesn't have the downforce your spoiler has. Your car has come along way in a few yrs. For some weird reason the pics and some of the words didn't show up on my work computer.

So less angle with a spoiler? I found a few posts from some forums but I can't pretend to understand it all. Here's one...

Rear Diffuser angles - TenTenths Motorsport Forum

This subject is really hard to solve without a full scale wind tunnel. Too much angle the airflow going out of the diffuser it disrupts the spoiler but you can get away with the angle by extending the mouth out away from the rear of the bumper. The greater the angle increases the total volume of diffuser. You might not need that much because the spoiler works with the diffuser. Too much of one makes the other less efficient, balance is the key. I would make the diffuser mounts adjustable so you can tune it rather than making it with one specific angle.

Here is a good place to read about different designs and the physics behind it all.
Diffusers | Engineering basics | Aerodynamics - Racecar Engineering

I ran across this video when watching one of their other shows awhile back. But it explains some more variables and it might help out.

Glad to see you have another how-far-can-I-go project. Sub'd to see how things progress.

If I read your description right, you plan on making the underside of the car as flat as possible. Will that provide any down force?

That's correct and I have no idea. I think it just ensures proper air flow under the car and around the tires and channels it to the diffusor so down force can happen. Besides that I'm waiting for style smart people to chime in.

Yeah I saw that. Only need $2000-$4000 to test everything. I also need to rake the car I think. I won't do that though till the flat bottoms done and I measure everything. If the flat bottom tapers up and back the whole way and I have this AOA on the diffusor I don't think I'll need rake because the under bellys doing it for me. Since this car had no diffusor though or flat bottom I may be at 100% rear DF.

Keep the strakes parallel all the way. If you were doing full cf mold you might benefit from molding them together to a point in the center, but unlikely. The point is to have the flow as smooth and linear as possible while accelerating the airflow under and out of the car.

Unless you have one crazy massive wing mount hanging it back several feet from the rear of the car, you're not getting any activation of the wing from the diffuser, so it's all about drag and air speed underneath the car. I'd put some small strakes at the end of the blades or just to the inside of the tires as well. Keep the air underneath from exiting along the doors and wheels.

As I said on Facebook. In all my models I lost attachment after 12 degrees or so, but your mileage may vary with real world testing. You can always use the string and GoPro test method :)


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And like that video, I'd be surprised if you're downforce wasn't very rear biased.

Fwiw, I could tell a significant difference at high speed just by having the airflow under the car smoothed and sealing off the flow into the rear bumper cavity. That was effectively a massive air brake at speed.


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You mean like this..... | | | | and not like this / | | \??

With string and a go pro what I am I looking for? What's it look like if you have lost attachment?

The plan right now is a full flat bottom and the flat bottom will extend past the side skirts maybe 4-5 inches. The diffusor will have 8 fins and so far all are parallel to each other and parallel to the ground. I'll finish today and post a pic.

What do you small strakes at the end on the blades?

In a way I actually don't mind it! My weight ratio is like 58/42. The rears to light weight from all the weight removal. In turns it sucks but I understand at high speed in a straight it can be and feel bad.