dual electric fan mounting question ?

1st, I would not recommend just putting a wall of metal for a shroud. You need to slope/swoop it like a nozzle/funnel. You need to give the air somewhere to go, not hit a wall....

another thing to consider is how much overlap the fan and shroud have. This a parameter that auto makers pay close attention. this is how much of the depth of the fan is overlapped by the fan shroud. This helps the fan pull the air through the radiator and shroud. You don't want the air going AROUND the shroud, but THROUGH it.... Start with half of the fan depth overlapped 50% (half in, half out) by the shroud and adjust to +/- 20%.

Now that it is going through the shroud, you need to keep it going, not hit a wall. This is why you blend the shroud fore/aft, so it directs the air to go through the path of the fan.

Otherwise you are not using the full capabilities of your fan.

Many auto makers put seals between the radiator and shroud to prevent any air "leakage" around the shroud.

Some of this may not apply to your electric fan appliction, but I wanted to show you the thought process to designing a fan shroud.