Fan hurting or helping ???
If You look up the Hall Chaparral CanAm cars, where they used 2 large 'cooling' fans that were actually generating a bunch of downforce,...You can get an idea of what You'd need to put on the front of the car to get any kind of meaningful input force on the car. Figuring the filtering thru' the rad, & the disorganized flow aft not actually applying pressure against the stationary ambient atmosphere, I'd say it has almost -0-% impact. You'd have to seal & streamline the nose of the car to & thru' the rad & the entire engine compartment, & have it exit underneath facing rearward, and I'm not sure it would get the car to move from a stop in neutral.
Point Your exhaust tips straight back & You'll probably get as much thrust/pull, with a lot less work,...but if You wanna try it, I'll follow along......:)