How do you get any aero downforce/less lift out of a ST185?

[OnAll-FOUR]

In regard to the vortex generators. Previously I have read through the www.autospeed.com four part series on them. I wouldn't imagine you would get much benefit from having them on the back as the EVO does because the GT4 hatch is quite a slow decline.

However i was interested by their idea of putting them on the underside of the front lip on the car. They reported that on a early model prius it made the car less effected by the was from other cars and trucks.

Another part I found interesting about that article was the wool tuffing they use to see the air flow at the surface of the car.

Sam Q - was this the article you were referring to?
http://www.autospeed.com/cms/A_2455/article.html

it also had this pick from a new Mercedes

[celicapain]

oh, my left nut for a wind tunnel.

[OnAll-FOUR]

I reckon It looks pretty sweet the vents from the engine bay, side exit exhaust all play their part.

[Sam_Q]

yeah thats it

[Andrew162]

howzabout an ST205 rear wing? similar to the wing posted in the first pics but slightly higher and definitely cooler. that, flat underbody, vortex generators underside of the body and rear of the roof line and you're well on your way. now get it up to 200km/h to make it all effective.

[OnAll-FOUR]

I think the rear wing is similar to celicapain's suggestion

I'm going to do some prototyping on the front undertray, baffels to direct air into the intercooler and the lumps/deflectors in front of the front wheels and i'll let you know how I go

cheers for the suggestions so far

[Roundy]

I think the rear wing is similar to celicapain's suggestion

I'm going to do some prototyping on the front undertray, baffels to direct air into the intercooler and the lumps/deflectors in front of the front wheels and i'll let you know how I go

cheers for the suggestions so far

make sure you take a template of them all

[Moppitt]

what materials will you be using for the underbody?

[OnAll-FOUR]

Probably plywood/MDF cardboard for prototyping,

For the final product, autospeed seemed to have some success with ABS plastic. can cut and shape with a heat gun easily, maybe some light aluminium ribs for reinforcement.

[TERRA Operative]

Time to disgorge my accumulated knowledge on this subject.....

The best shape for the duct for an intercooler/radiator or whatever isn't a funnel shape. What you want is an inlet area at approximately 25% of the total core area (or slightly more). So you end up with basically a backwards funnel.
By doing this, you slow down the air as it depressurises, making it stay in the core longer to absorb more heat. It also ensures that the air doesn't simply pile up in front of the core as a high pressure region and end up going around. A well designed duct like this can theoretically gain up to 15%-20% in efficiency versus no duct. In practice, the gain will be around 5%-10% or so.
Imagine having a core of 1000mm x 300mm, with a duct opening of 1200mm x 500mm. there is no way you will get all that air flowing through that restrictive core. By using the 'inverted funnel' you will ensure that all the air that goes in will go through, and won't simply go around or get piled up creating excessive drag.

Of course, that doesn't end up effecting aero too much.

For bonnet vents, you want the exhaust vents as far forward as possible. The reason for this is, as the air from the front of the car comes up over the bonnet, it creates a low pressure region in the first 30-50cm or so before it relaminates to the bonnet, effectively sucking the hot air out. The vents on the Evos are fairly well placed, but many aftermarket bonnets have the vents way too far back. A well designed vent will also help prevent under bonnet temps getting too high, which can be good with a big turbo in a small bay....

For intakes, you want the scoop placed as far back on the bonnet as possible. Further back than even the WRX would be ideal. As the air hits the windscreen, it piles up and creates a high pressure region. You can often see positive manifold pressures of up to 2psi with a good sealed intake setup (ITB's on a FWD Corolla will be easy to set up like this). It's one of the reasons the intake for your cabin ventilation is there.

For underbody trays and aero etc, you want the front lip as close to the ground as possible, a front splitter will help direct air up and over and into your intercooler too. A 10cm lip is fine.
What you want to do is prevent as much air getting under the car as possible, this will help create the low pressure region you want. Low side skirts will help to prevent air entering from the sides too.
At the rear, try to sweep the tray up towards the bumper to create a funnel effect, so the air will depressurise further. Just be sure you incorporate some sort of vane system or guides to prevent turbulence (like in that BMW pic posted earlier).

Wings are ok, but they create lots of drag, which underbody aero helps prevent. The main concern with rear wings is to keep them out of turbulent flow, hence the massive dorifto wings ricers tend to use. Yea, they actually can work...

The reason the Evo uses those vortex generators along the rear windscreen is to help maintain laminar flow over the rear windscreen and boot lid. This allows a lower profile rear wing which helps lower drag (and increase looks...).

When we come to the trailing edges, you want a sharp edge to flick off the laminar flowing air. Cars with a smooth curve over the back of the boot lid tend to hold the laminar flow over the back which causes an eddy flow of air creating a low pressure area which effectively tries to suck the car back. With a well designed boot lid or lip, the air behind the car is left at a more constant pressure which doesn't tend to create this effect.
You will see many modern sedans with this lip, and many hatches with a lip above the rear windscreen.

Vortex generators can be used along most leading edges where turbulence will result due to that edge. Good places are along the top of the rear windscreen and under the front lip. They are good in that they don't add significantly to drag for their positive effect (Unlike a rear wing).

I hope that helps a little. If there's something blatantly wrong, let me know. Even I aren't perfect.

[EDIT]
Oh, if you do make a full underbody tray, or even just the size of the engine bay, make sure to include vents like in that BMW pic. above.
You don't want the rear part of the engine bay acting like a parachute and holding all that hot air from the engine....

[OnAll-FOUR]

Time to disgorge my accumulated knowledge on this subject.....

The best shape for the duct for an intercooler/radiator or whatever isn't a funnel shape. What you want is an inlet area at approximately 25% of the total core area (or slightly more). So you end up with basically a backwards funnel.
By doing this, you slow down the air as it depressurises, making it stay in the core longer to absorb more heat. It also ensures that the air doesn't simply pile up in front of the core as a high pressure region and end up going around. A well designed duct like this can theoretically gain up to 15%-20% in efficiency versus no duct. In practice, the gain will be around 5%-10% or so.
Imagine having a core of 1000mm x 300mm, with a duct opening of 1200mm x 500mm. there is no way you will get all that air flowing through that restrictive core. By using the 'inverted funnel' you will ensure that all the air that goes in will go through, and won't simply go around or get piled up creating excessive drag.

Of course, that doesn't end up effecting aero too much.

Okay you go me there, I was going to build it the other way round. Although having said that, my radiator and intercooler stretch up behind my front bar without any direct airflow. so if I build it with stright sides, that should give me the 25% increase in area anyway. I'll try it out.

For bonnet vents, you want the exhaust vents as far forward as possible. The reason for this is, as the air from the front of the car comes up over the bonnet, it creates a low pressure region in the first 30-50cm or so before it relaminates to the bonnet, effectively sucking the hot air out. The vents on the Evos are fairly well placed, but many aftermarket bonnets have the vents way too far back. A well designed vent will also help prevent under bonnet temps getting too high, which can be good with a big turbo in a small bay....

Possibly a carbon group A celica bonnet with the vent design on the way so that would help there.

For intakes, you want the scoop placed as far back on the bonnet as possible. Further back than even the WRX would be ideal. As the air hits the windscreen, it piles up and creates a high pressure region. You can often see positive manifold pressures of up to 2psi with a good sealed intake setup (ITB's on a FWD Corolla will be easy to set up like this). It's one of the reasons the intake for your cabin ventilation is there.

Not so easy on the GT4 but I will think about it. I did have one thought of turnning the old ATA topmount bonnet scoop into a air intake?

For underbody trays and aero etc, you want the front lip as close to the ground as possible, a front splitter will help direct air up and over and into your intercooler too. A 10cm lip is fine.
What you want to do is prevent as much air getting under the car as possible, this will help create the low pressure region you want. Low side skirts will help to prevent air entering from the sides too.
At the rear, try to sweep the tray up towards the bumper to create a funnel effect, so the air will depressurise further. Just be sure you incorporate some sort of vane system or guides to prevent turbulence (like in that BMW pic posted earlier).

Wings are ok, but they create lots of drag, which underbody aero helps prevent. The main concern with rear wings is to keep them out of turbulent flow, hence the massive dorifto wings ricers tend to use. Yea, they actually can work...

The reason the Evo uses those vortex generators along the rear windscreen is to help maintain laminar flow over the rear windscreen and boot lid. This allows a lower profile rear wing which helps lower drag (and increase looks...).

When we come to the trailing edges, you want a sharp edge to flick off the laminar flowing air. Cars with a smooth curve over the back of the boot lid tend to hold the laminar flow over the back which causes an eddy flow of air creating a low pressure area which effectively tries to suck the car back. With a well designed boot lid or lip, the air behind the car is left at a more constant pressure which doesn't tend to create this effect.
You will see many modern sedans with this lip, and many hatches with a lip above the rear windscreen.

What would you recomend for the GT4. this pic gives an idea of the side profile,

Vortex generators can be used along most leading edges where turbulence will result due to that edge. Good places are along the top of the rear windscreen and under the front lip. They are good in that they don't add significantly to drag for their positive effect (Unlike a rear wing).

I hope that helps a little. If there's something blatantly wrong, let me know. Even I aren't perfect.

[EDIT]
Oh, if you do make a full underbody tray, or even just the size of the engine bay, make sure to include vents like in that BMW pic. above.
You don't want the rear part of the engine bay acting like a parachute and holding all that hot air from the engine....

[TERRA Operative]

Evo style vortex generators will help maintain lamination over the large rear windscreen, maybe a rear wing that sits a little higher.

The central intake should work ok. It's not as far back as ideal, but the airflow over the bonnet should have relaminated by then, so it will be out of the low pressure area.
Just make sure the hot air from the vent doesn't get sucked straight into the intake. Ideally, the intake will be sitting at the rear-centre of the bonnet, with the vents near the front corners.
Or stick the intake behind the headlight somewhere if you have a large front-centre located vent. Just be careful not to suck hot air off the road....

[Classique71]

If you need a pic side on of the back end of a St205 Group A ( which has an effective , and practical rear wing ) let me know - It can be provided for reference and you'll see exactly what the toyota Engineers used to keep the St205 firmly planted on the road at over 200 KMH in racing conditions

[OnAll-FOUR]

The front splitters are the first of many updates.



And have a starting point for the rear

[Moppitt]

Is that rear bar custom or is that diffuser off another car? and how far forward will you extend it?