Mustang Tech

fan space......... i am putting a twin thermo and alloy shroud on my mustang clevo, is it better to have the shroud with a 25mm gap between core and fan shroud or is it better to have as much space between core and shroud as i can get to pull air more evenly across a bigger area and i have the room to double the distance

Not sure you have the question right. The shroud should be sealed to the rad so the fan pulls all the air through the core. The fans being electric (I assume) would be part of the shroud? If not, the fan should have half the blade (seen across the shroud) visible.

Hope that makes sense.

25mm should be enough thickness for your shroud, but I'd go a bit deeper if you have the room. Maybe 30-40mm.
The biggest factor is how much of the area your fans will take up though. If they take up most of the room then the air should easily flow through the fans on the highway. If they don't, you can have issues with the shroud blocking the airflow. That's why some guys put flaps in the shroud that will open up when the car is moving fast enough through the air, but be closed when the fan is running.

This is an example of what Hybrid is talking about that I made up for a 16" Spal on a big block radiator in my 66. I replaced it with a dual Mondeo fan I found at a Ford wrecker.

I only had limited depth, deeper would be better. I found no difference in cooling down time between bolting the fan directly to radiator or making a box to seal it and set it back?

I made a single flap mockup unit and went for a ride on my motorcycle to check that I had enough weight on them to stop them opening under 40 kmh.