at what speed do you think thay would help?
why dont more people use it?

how big of 1 is needed?

In land speed stuff its not really for downforce it just to keep air out from under the car. A real land speed car wants little downforce as possible. The more downforce the more power it robs to push the car. That is why most speed cars are heavy tanks. My buddy's Bonneville car that goes 320 MPH weighs 5200 lbs and has such little down force it only compresses the shocks 1/2 inch at that speed. I think it has different affects and outcomes in dragracing.

Last months issue of Racecar Engineering had an in depth article on aero devices at relatively low speeds, with the hill climbing crowd in mind. They reported measuring downforce beginning at 30-40mph, and of course its quantitative effect is very speed dependent. I was suprised.

thanks jcc i will try to find it.

here is the link on the camaro.
http://www.google.com/url?sa=t&sourc...D2DXZCs-Li5l80w

i can understand some not wanting to block there grill/radiator in part or all but a valance /spoiler can only help it looks like.

when i fitted my current spoiler i could definately feel the steering get heavier at speed.

Front spoilers reduce lift by coaching the air around the car instead of under it. The absence of lift could be considered downforce but it's not really. Think of it as being a car with 2000 lbs nose weight but at 70MPH the lift it experiences effectively makes the nose weigh 1800 lbs. A spoiler reduces or eliminates that lift. Downforce means that there is now say 2200 lbs on the nose as the car moves through the air. Splitters and such are typically downforce generators, as would be the example of a car where the radiator is ducted so that air escapes through the hood against a panel. Look at the Euro Touring car series for an idea of how they manipulate air for downforce, especially the DTM (German Touring Cars).
A rear spoiler like on the 1st-gen Camaros & etc actually causes the air coming over the roof to hit the trunk lid, as well as breaking up the eddy that forms behind the car. The trade-off with rear aero devices, as well as big cooling openings & add-ons like mirrors & etc is drag.
To an extent, you can think of a car moving through air as a stationary object in moving water, although it's a bit more complicated than that, which is why the better wind tunnels now use moving floors.

if you still blocked the grill you could divert air from the spoiler into the rad and still have enough cooling i would think unless you used a curtain style and just diverted the air.