Not sure about caddy specific, but other vehicles use them and are called "air dams" so it builds pressure and you can see wind tunnel diagrams where...
Am looking at the ads and not sure if I should try the spit or single on an 82 diesel pickup.
What do they actually do other than look interesting? ...
will have a similar range as a Caddy, but will cost you twice as much to fill it as they had a 20 gallon tank, some even had dual tanks so could hold...