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Old 12-03-2007, 09:46 AM   #176
Scooby South
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also...nhluhr has some Aero Data...Search his name and Aero
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Old 12-03-2007, 09:55 AM   #177
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I think mine has at least 20 pounds of down force, or at least as much as it weighs
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Old 12-03-2007, 11:31 AM   #178
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If someone can get me a good 2d or 3d model of the car, I can tell you theoretically how much lifting force (both positive and negative) is acting on all surfaces of the car.
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Old 12-03-2007, 01:12 PM   #179
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taco bell added 20 pounds of downforce to my rear end last weekend and it was brutal.



hehehehehe...

no wing on my sti and its fine. you wont see me taking any long sweepers above 100mph though. definitely not.


almost any aftermarket wing that is a quality piece will be much more beneficial and adjustable if you are serious into track use.
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Old 12-03-2007, 02:10 PM   #180
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with the lower lip and stock wing, my 06 STi is incredibly stable at 120-140 ... with an added STi Rubber Skirt Lip, Rallispec says even more wind-cheating. Looking at the competition during track time, the track-dedicated 911s have monster wings that make the STi's look 1/2 as small ... i wonder, if a larger wing, like on the AMS Evo, is that much better for dedicated track use?
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Old 12-03-2007, 04:00 PM   #181
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i can save us all the time of speculation if I could get an accurate 2d or 3d model to run in CFD.

Increasing area does increase lift production, but also drag. It should be noted that wing should be put in "clean air" wich often results in a raised height over the roof. However, if put in proximaty of the rear diffuser, overall rear lift (downforce) production can be enhanced. Probably need a boundary layer energizing device to put the wing in "clean air" if location is below the roof.

You also have to remember that aerodynamic forces with affect the dynamic weight distribution of your vehicle as your speed changes. Your also changing your moment coefficient about your cg which will affect weight transfer at speed. This will greatly affect your vehicles characteristics in a corner it can either help or hurt your the lateral acceleration your vehicle can obtain ie can induce oversteer, understeer or promote nuetrual steer.

Last edited by stark22; 12-03-2007 at 04:09 PM.
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Old 12-04-2007, 01:13 AM   #182
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My set up is competitive enough for now, time wise, but will have KW V3s by next season. Now on Swifts, -2.7/-2.5 cambers (even though on this day rear was set to -3 for the high speed Speedway banking). Still, cold and moist conditions on Hoosier R6s really made the rear felt too 'light' at 130-140 mph, at California Speedway.

I do have the sharp-lipped v-limited replica which actually work keeping the front end down, but seems to need a bit more rear downforce.



on the Roval banking at just over 130 mph
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Old 12-04-2007, 01:26 AM   #183
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Nice pics.

You should get the roof vane from the 06-07 STI that will help make your wing more effective. You could also look at getting the SYMS (or replica) STI wing insert that you can adjust the angle of the top part to increase more downforce. You might want to add the rubber skirt on your V-LTD because more downforce on the rear acts as a lever and your front end will see more lift.
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Old 12-04-2007, 08:16 AM   #184
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The v-limited lips don't provide downforce as much as they reduce lift by limiting underbody flow. You need a splitter, canards, or an aggressive front lip to create downforce.

To clarify, creating downforce does not equal reducing lift. They can have the same end effect, but a mathematical analogy would be:

creating downforce: 3 (lift) -2 (downforce) =1
Reducing lift: 1 (lift) -0 (no downforce) =1

they have the same net effect, except the sum of "creating downforce" can become negative, while lift reducing elements can only go to zero, and not negative.
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Old 12-04-2007, 09:32 AM   #185
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Quote:
Originally Posted by Mechie3 View Post
The v-limited lips don't provide downforce as much as they reduce lift by limiting underbody flow.
I agree on that. Before I installed the lip spoiler, at the same track, the front end would push when rounding the banked oval. And, on the front straight, where I pegged at ~145 before the banking, the front end felt less planted, more nervous. The v-lip definitely stabilized the front end. I just think I need slight adjustments at the rear wing (increase angle of attack - APR, SYMS?) to give me a little more downforce.

Butt dyno is a pucker one when track surface is slick I don't want to kiss the wall at those speeds.

Last edited by MaxSTi05; 12-04-2007 at 09:44 AM.
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Old 12-04-2007, 10:22 AM   #186
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I generated a 2d model.

I will attempt to run in a CFD software by the end of the week and possibly post some static pressure plots over the car.

If you want to reduce lift in the front, louvres (fish gills) on the hood will help.
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Old 12-04-2007, 12:49 PM   #187
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I have the Syms replica rear wing and I can confirm that it does work, and the angle does make a difference. I had it set in the middle setting (it has 3), and after turning it to the steepest setting the car was noticably more planted in high speed corners and under braking at the end of high speed straights. This was most noticable at VIR going up the Esses, and braking into 14 after the long back straight. I definitely need to get a front lip of some sort. I REALLY like the new APR, bit it's pricey for something that's going to get beat on.

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Old 12-04-2007, 02:36 PM   #188
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See attached numbers from FoilSim based on the wing geometry.

Street STi wing

http://img.photobucket.com/albums/v3.../STiWing-2.jpg

Rough estimate of WRC wing (no first hand wing to get geometry from)

http://img.photobucket.com/albums/v3...TiWing-WRC.jpg

Note this is just for the wings themselves with no consideration of the lift and turbulence from the body.
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Old 12-04-2007, 02:43 PM   #189
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my butt-o-meter definitely noticed a difference...i ran 130-ish with and without the wing and i'm surprised how much better planted it feels, even on a simple straight away.

*I know this isn't cold hard evidence, but I definately noticed a difference at somewhat faster than normal freeway speed.

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Old 12-04-2007, 02:54 PM   #190
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Quote:
Originally Posted by Grintch View Post
See attached numbers from FoilSim based on the wing geometry.

Street STi wing

http://img.photobucket.com/albums/v3.../STiWing-2.jpg
So, we're looking at appx 50 lbs and 90 lbs of downforce at 100 and 150 mph, respectively. I'm assuming factory rake on the wing. Not bad. Does anyone have numbers from the SYMS or APR at their different angles?
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Old 12-04-2007, 06:45 PM   #191
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If anyone wants to host some pics later tonight, ill have some 2d flow analysis over a 2004 STI.

Let me know.

Also for the calculations above, they don't predict stall and the rear wind is not in "clean" air. Also due to 3d affects the wing is not as efficient. But it is a good place to start.

Last edited by stark22; 12-04-2007 at 07:15 PM.
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Old 12-04-2007, 07:46 PM   #192
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Quote:
Originally Posted by Grintch View Post
See attached numbers from FoilSim based on the wing geometry.

Street STi wing

http://img.photobucket.com/albums/v3.../STiWing-2.jpg

Rough estimate of WRC wing (no first hand wing to get geometry from)

http://img.photobucket.com/albums/v3...TiWing-WRC.jpg

Note this is just for the wings themselves with no consideration of the lift and turbulence from the body.

Wow! Now I can see why those vertical supports are so important on the WRC wings. .... 400+lbs at 100mph.
A way you could really tune your front end downforce would be to go with v-limited and put a CF splitter underneath that. Even with 1/2 to 3/4" protruding underneath the lip you would be adding a good amount of down-force (plus the splitter is adjustable) and add a small rubber skirt to the bottom of the CF splitter to further minimize airflow under the car depending on how much clearance you have. Getting the sides covered up will also help keep air away from the underside of the car and reduce lift. As far as planting the rear end, IMO go with the SYMS or you could at some vortex generators to the back end of the roof so your stock spoiler can get more "clean" air.
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Old 12-04-2007, 08:15 PM   #193
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I know this isn't cold hard evidence - but as some of the other said, I think the Syms wing works better too. When I first drove my MY07 STi at 120 I was amazed at how much more smooth it was at that speed than my MY04 STi.

I later added a Syms wing and at highest setting it felt almost identical to the OEM wing at speed (this is all straights with no cornering) - I basically couldn't tell difference. When adjusted to lowest setting causing most downforce I noticeably could tell at speed. It felt even more planted at 100+. Would love to add the APR front lip to further increase stability at speed...

I would be curious to see results if you could run the Syms wing through the same model above.
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Old 12-04-2007, 08:27 PM   #194
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heres a quick snap shot. Itll be done hopefully tomorrow if the solution converges. No Wing, no rolling road, no wheels. Just to show static pressure over the body. This is not the final solution...just a snap shot of a iteration. Ill try and post the final results tomorrow night.

If time permits I will validate with another code to see if these results are "accurate". I would really need to compare to empirical results.

Then you can put in any splitter, wing.....and have numerical results and know what exactly your aero mods are doing.
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Old 12-04-2007, 11:21 PM   #195
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Quote:
Originally Posted by Mechie3 View Post


Speeds are 60 and 90 mph? Can't remember.
Wow. If I understand this correctly, both cars show obscene front lift. Would love to see the same data for the new Sti. Subaru says it has zero lift. That would mean quite a lot compared to 500 pounds of front lift! I hope they don't mean "net lift" as in the sum of front and rear lift/downforces. That would basically mean the new car is potentially just as lopsided as the old car and Subaru is just summing them. That would be pretty lame...

Frank
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Old 12-05-2007, 01:45 AM   #196
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Quote:
Originally Posted by stark22 View Post


heres a quick snap shot. Itll be done hopefully tomorrow if the solution converges. No Wing, no rolling road, no wheels. Just to show static pressure over the body. This is not the final solution...just a snap shot of a iteration. Ill try and post the final results tomorrow night.

If time permits I will validate with another code to see if these results are "accurate". I would really need to compare to empirical results.

Then you can put in any splitter, wing.....and have numerical results and know what exactly your aero mods are doing.
Stark, this is awesome!

Which CFD package is this? I'm in the process of getting a license from NASA (no, I'm not joking you ninnies) for TetrUSS to try to do exactly this same thing for my 05 wagon. How did you come up with a profile of the car? How much does simplifying the profile to a flat bottom matter? How much does not having flow into the grille and hoodscoop matter?
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Old 12-05-2007, 07:59 AM   #197
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I'm actually not at liberty to say which CFD package this is. Sorry.

I came up with the profile by loading a picture of the car into a sketch plane into my CAD software. Then I put points at specific locations. Then I ran a spline curve and adjusted to points to best fit the body contours. This is not the most accurate method but it works for now.

Simplifying the underside of the car actually increases negative lifting effeciency. The underside is behaving like a diffusor. There are no oil pans, a-arms or exhaust to distrupt/distrub the flow.

Flow into the girl should not matter that much, i believe. The stagnation pressure should be in the same location however, slightly lower due to some flow through the grill.

Hood scoop as well will have less static pressure. Also no flow through the scoop will affect how well the flow stays attached to the body aft of it.
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Old 12-05-2007, 08:19 AM   #198
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Quote:
Originally Posted by stark22 View Post


heres a quick snap shot. Itll be done hopefully tomorrow if the solution converges. No Wing, no rolling road, no wheels. Just to show static pressure over the body. This is not the final solution...just a snap shot of a iteration. Ill try and post the final results tomorrow night.

If time permits I will validate with another code to see if these results are "accurate". I would really need to compare to empirical results.

Then you can put in any splitter, wing.....and have numerical results and know what exactly your aero mods are doing.
for us non-aero types...can you explain the different colors....I assume they are high and low pressure areas...and what the effect of those pressure areas do...


Bill
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Old 12-05-2007, 08:48 AM   #199
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Quote:
Originally Posted by Frank A View Post
500 pounds of front lift!

It's not 500 lbs, not sure what the units are. The article was in Japanese. It's just useful to show relative forces.


Nice work Stark. It'd be interesting too to see how the 06 and 08 profiles do with your CFD program.
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Old 12-05-2007, 10:02 AM   #200
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Quote:
Originally Posted by williaty View Post
Stark, this is awesome!

Which CFD package is this? I'm in the process of getting a license from NASA (no, I'm not joking you ninnies) for TetrUSS to try to do exactly this same thing for my 05 wagon.
Have you used anything like TetrUSS before? Have you taken boundary layer courses? Do you have serious hardware to run it on?

We use TetrUSS and have needed years of experience to get a solution that mimics reality.

Just want to make sure you know what you're getting into.
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