Using both a puller and a pusher fan together is inefficient! I know there are the guys running both that will give you their example and testify how their car runs great. But the reality is it's not the best way.
Considering the fact that once the car gets moving at even slow cruising speed the fan does nothing to provide air flow across the radiator because the moving air from driving is greater than the amount the fan can provide. In a typical electric fan system the fans turn off once the preset temperature is achieved. The system is now relying solely on the moving vehicle providing the air flow to cool the radiator. Even with a solid mounted mechanical fan it's not pulling the air through because it can't keep up with the air flow when moving. That's why they started putting thermostatic clutch fans on cars. The fan just free wheels and spins like a pinwheel at cruising speed. It reduces the parasitic loss.
The point is that every fan has a threshold where it can't move any more air. At this point it just becomes an obstacle and causes turbulence. So getting back to 2 fans pushing and pulling. The fan that moves more air will over power the other fan and that fan becomes the obstacle. You would do better just having the fan that moves the greater amount of air and ditch the other. A well designed fan shroud is of major benefit as is a good air tight seal surrounding the radiator. Any radiator without either is at a disadvantage and the system loses efficiency.
