Increasing downforce while reducing drag?

[MechEngVT]

Hot Rod magazine did some good wind tunnel testing with a Model A roadster that was prepped for salt flat racing. They listed some common mods and the resulting affect on Cd and lift. Last time I checked they had the full article online if someone wants to try to find the link to it. There were several Hot Rod articles on wind tunnel testing, all of them fairly decent.

[NeilBlanchard]

Hi Hermie,

Vortex generators add drag and they add (a little) frontal area. You can try them -- I would do tuft testing, but my guess is that you will either notice a slight loss of FE or have no change. I very much doubt if you will gain anything in the handling department. Any wing that adds downforce will also add drag -- or you might just get the drag and no added downforce.

[2003protege]

Originally Posted by evolutionmovement

The Audi TT in question was notorious for high speed lift-off snap oversteer due to the style-over-function design. After that incident (not the only one), the optional rear spoiler was installed on all of them by the factory.

Indeed: Clarkson on: the Audi TT - BBC Top Gear

Originally Posted by Hermie

I know there's got to...give downforce while reducing drag.

basically impossible. Lift or downforce is created by air having to travel at different speeds around an object. The slower air is at a higher pressure than the faster moving air giving a net force. to alter air's speed, it must encounter added surface friction or have it's direction changed through some force imposed by the surface of the vehicle.

The more you work toward a net-zero drag/lift situation at speed, the more you will reduce drag, although I would always err on the side of downforce.

I'm planning on doing a boattail *someday* and lift is my biggest concern, currently.

[Hermie]

Neil- I was thinking a simple lip spoiler, not a wing. Wings are too big for a car like this.. :P

[rmay635703]

Originally Posted by Hermie

OEMs won't cover ANY modification of the engine that isn't replacing OEM parts. I'm quite sure your lack of an air filter isn't covered either, so what you said is pointless.

"I'm sure you were referring to blocking the air inlets of the grille, which, in most OEM "real world" scenarios, are far too large to allow for adequate cooling."

That makes absolutely no sense. Go ahead and pull off your front facia. I'm sure you'll be running plenty cool from all that air hitting the radiator. If you said "small," it would make sense.
Unless the engineers are complete idiots, a large grille allows a large ammount of air into the engine compartment and through the radiator, thus allowing better cooling than a smaller grille. Common sense.

Its not the engineers that are ideots, look at the dodge v8 5.2 pickups out there, the grill is much larger than the radiator. It doesn't take a rocket scientist to figure out design and appearance play a bigger role than what is absolutely necessary. Also many FWD cars get most of their air from UNDER NEITH the car not from the grill.

Also I am certain Ford isn't going to cover your 91 Tempo even if you don't modify it anyway. Most of us are certainly far from the manufacturers warranty.

[NeilBlanchard]

Hi Hermie,

Originally Posted by Hermie

Neil- I was thinking a simple lip spoiler, not a wing. Wings are too big for a car like this.. :P

Well, tuft testing will let you know if it works. Tuft test as it is now, and then make a lip spoiler and test it again. I doubt that the trailing edge of the trunk on your car has attached air flow, and so the lip spoiler probably will not change anything.

Now maybe a Kamm back...

[evolutionmovement]

Maybe a small lip spoiler would reach the airstream and cause reattachment.

Though I put on an airdam (ABS plastic and alloy with 1/4 turn bolts for removal), the full undercarriage cover would probably be a better bet and wouldn't cost you ground clearance.

[Deezler]

Hermsters,

I decided to try some VGs on my Jetta.
http://ecomodder.com/forum/showthrea...rear-8839.html

No definitive mpg improvement, but a major fuel change impaired any possibility of a good comparison.

Also recently added a mediocre rear diffuser. This made a more noticeable improvement, vs the parachute stock rear bumper lip.
http://ecomodder.com/forum/118456-post34.html

[Hermie]

Checked out your thread, and your Jetta's rear end is a heck of a lot smoother and not as sharp of an angle as my Tempo's. I'll do some tuft testing when I can. Couldn't today, though. You can tell the VGs made a difference with airflow sticking.

I want to make sure the air reattaches on the decklid. If not, there's a real drag problem there, and I could make massive Cd improvements with VGs.

I'm also looking into some material from Rubber Cal for an air dam and side skirts. I ordered a couple of samples so I can see which will hold better and be easier to work with.

Those were also the brand of VG's I was looking at. They're pretty cheap on Ebay.

[robchalmers]

I'm a little confused by this thread.

Do you really want to add DF?? was that increase the point weight on the tyres and therefore the rolling resistance. I would suggest a ballanced approach go for a froint air dam but increase the size of it slowly in steps. chucking a large one at it may result in a the car become twitchy as you've increased front end grip but the back is relatively light in comparison - which brings me the the TT. As stated above the design is a form-over-function golf in drag but it is a very short wheel base car with alot of the weight over the front wheels allowing a huge amount of direct direction change. at Autobahn speeds of 150 MPH (yes MPH not KMH) any golf-size car will get twitchy but I'm stunned they didn't find this out before putting it on sale.

I'm shocked that you car gets wayward at 80! I've had some beaters in my time and all of them have been planted well beyond that ( where legal limits allow ). even my little polo stays glued on 175 tyres at GPS indicated 103 mph (more than book says it can do!!!) and cross winds at 80 don't phase it.

Another suggestion to cure its road manners maybe a new set of struts and lower the ride height, over soft shocks can make it a car raise-up at speed and therefore give a feeling of a lot less control.