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Yes, you are correct about that.
There should be a containment ring around the blades that has a depth that reaches to a minimum of half way down the fans axis or behind any outward flow from the periphery.
The idea is to contain the outward boundary of air to compress the mass more uniformly across the fan blades face. The compressing helps create a low pressure area within the rotating blade mass.
The shroud also acts also like a funnel. The larger area ahead of the fan, that in our case is square, needs to capture that low pressure area so it pulls air from the corners utilizing the extreme ends of a cooling row in the heat exchanger. The fans distance from the cooling core is somewhat critical. There is an optimum allowance for curve flowing and working with an operational speed "bell curve" to be efficient.
You will see the rear section of the shroud is extended slightly more but it's really for the motoring public safety. Once the air is pushed then its studied and considered a frictional drag.
Do not forget a purpose for underbelly pans as air flow controllers. They can be very effective depending, on their designs for cars with those smaller grill areas showing up that can intrigue you to wonder, from where they are getting their air?
On the 240's I think they help only with their low slung alternators. As they can keep a "whirly world" of crap from getting inside and on the belts too!
I figure it this way, as "cheapskate manufacturers" usually are, if they spent their bottom line money on it, there must be a reason to have it.
Otherwise, given the chance, they would toss it like the last drag on a borrowed cigarette! (:-|)
Phil
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