Like that thick rubber spoiler under the car. I had one like that on my mid engine Corvair. Is it straight across? Maybe setting it as a V shape to push the air out the sides. The roof spoiler is not so much for downforce, but to disturb the airflow around the car and push the flow up and behind rather than curling around the back of the car. Need some more horsepower but I think I can accomplish that with a different tune and methanol injection. Car was real strong and you can tell it has another 20 mph in it.Maine.jpg