What size is this car you're working on?

Are you wanting horizontal thrust, down thrust (for traction) or both?

FYI: Chevron (race cars, not the oil company) got outlawed from Can-Am racing in the early 70's for having a car that was BB Chevy powered (510cid) and had like a 4 or 5 foot fan in the center of the car mounted flat to pull air up from the track. Working with hard rubber seals around the outside lower body work it was most effective. They were known as the vacuum cleaner cars. They dominated 'till they got outlawed for throwing debris straight up off the track. That was the official reason anyway .

I don't know if this type design might help or not. I hope it at least amused someone. I am the king of useless information! Just ask my wife...