I assume you mean venturi effect. It could be done. All you have to do is increase the velocity of the airflow under the car. That can be achieved by creating a tunnel, constricting the air as it exists the engine cavity. The air has no where to go but that hole. The area of the intake is smaller than the exhaust, so the velocity increases. Wala an increased differential in the velocity under vs over the car resulting in downforce. We would still have to worry about making the hole too small, overheating the engine.

I would imagine the reason they put channels is to direct the airflow to minimize drag. In a sense keep less negative pressure on the ass end of the car. This resitricts the air from curling back behind the car, creating drag.

I believe there was an attempt to use active aerodynamic enhancements, but it was quickly banned.

 

[QUOTE]Originally posted by outoforder
[B]bbsilver,

Exactly: a giant X brace between all four wheels, but really thin.

Here's the page on dual-lock: http://www.3m.com/us/mfg_industrial/adhesi...0709-3869-4.pdf

Dynamic shear strength is 31.7 PSI, which is good.

 

That would do part of it. A cross brace would be more effective. They have basically stiffened the stiffest part of the car. The bigger problem is a torsional flex.

A CF version of that would be easier to jig and that would be STIFF and light. We could make it out of four smaller tubes and bolted in the center, that way we could accomedate cars that aren't quite up to the factory specs (racing, wrecking etc).

 

bbilver,

I was just calculating the weight of the velcro, not the carbon fiber panel. The panel would weigh quite a bit more -- I'm hoping for 20-30 lbs. including adhesives, fasteners, carbon fiber, matrix, and foam/honeycomb/whatever.

I've been thinking about the aero problem, and it's a big problem, as ScienceOfSpeed pointed out. Airflow between the sheet and the existing underside is going to be very high drag, and there is not much room to expand any airflow after contact with the cat and resonator. Also, any such clever ducting is going to involve sticking complicated shapes up off the top of the sheet up near stuff that likes to jiggle around, a sure recipie for cost and rattles.

I think some small amount of downforce is possible simply by reducing the amount of drag (and therefore increasing the speed) between the sheet and the air between the ground and the sheet, but for most of the length there is just no room for actual expansion. There is also the opportunity to positively guide engine compartment airflow laterally out, which would clear some of the air mass out from under the car.

However, I think the potential for just bracing the chassis is definitely there. For this application the sheet would just run between the front and rear lower A-arm attach points, between the two exposed frame rails. It would have a few largish holes down one side to vent the air cooling the catalytic converter. Somehow, and I don't know how, it has to connect compressive forces up to the frame rail running over the driveshaft between the front seats. Maybe I'd hang a torque tube/box just outboard of each frame rail, but probably not, since I bet you just can't couple the torque stiffness into velcro fasteners that fundamentally have to peel off.

I'm thinking velcro all under both front-back frame rails, under the transmission mount, and then somehow couple the sheet to the X brace and rear brace mount points. Hmm... 300-400 square inches, so about 9000-12000 pounds of shear strength, which is probably about right. Maybe the front and rear mount points get actual bolts, so maybe torque tube/boxes do make sense. But my intuition says that you let the CF deliver tension loads between the four corners of the car, and let the steel frame take care of the rest.

 

[QUOTE]Originally posted by outoforder
[B]bbilver,

I was just calculating the weight of the velcro, not the carbon fiber panel.

 

well I agree that more bracing the better. Like on my 98 trans am, it benefited a lot of hotckis braces. Any idea if this undertray will be produced?

 

Look under an E46 M3!!!

They replaced the multipoint x-brace with an aluminum plate. many attacment points, single to double shear benefits and aero effects.

'Course it's only under the front portion of the car.

Stan

 

bbsilver,

Tell us a little more about cost. I'm familiar with fiberglass, and I had assumed that CF was simply a matter of buying more expensive mat and perhaps more expensive CF compatible matrix. Am I off in the weeds? How much is a 36" by 100" by 0.1" plain sheet of CF (about 360 cubic inches) going to cost, neglecting any fasteners?

And, do you have any stress/strain info, or a pointer to a web page with material specs?

 

[QUOTE]Originally posted by outoforder
[B]bbsilver,

Tell us a little more about cost.

 

Does anyone know for sure how the front and rear subframes are connected to the main chassis? Does the service manual show anything conclusive? The subframes on my car are painted black, in contrast to the chassis which is, of course, body color. It might just be that they are manufactured seperately and then bolted or welded together. This page suggests as much:

http://www.honda.ca/models/s2000_benefits_...description.asp
"The front and rear portions of the central frame and the side sills tie into diagonal braces (X-braces) at the rear of the cockpit and at the front cowl. These X-members connect directly to the front and rear suspension subframes."

...On the other hand, that page has some mistakes and in general looks like it was written by marketing, and it seems odd to me that the subframe would be painted and then welded, which suggests it is just bolted, which doesn't give me a good feeling. Nor do the parallel front crossmembers ahead of the front wheels, one for the subframe and one for the chassis.

If the subframes are vibration isolated from the main chassis, any brace that connects the two is (a) going to add noise, vibration, and harshness, and (b) probably going to break either itself or something else. This could be a showstopper.

On the other hand, if the subframe is bolted to the chassis, then a straight brace has lots of potential, since the existing force path winds around a fair bit.