I would think it wouldn't matter what size engine you had a given set-up bolted up to. It would take the same amount of hp to drive that fan/shroud/rad combo at a given rpm. The engine is just the device that turns the fan. The amount of power it takes to turn it is a function of how many cfm the fan is trying to move through a given resistance to the airflow. That's why the amount of hp required dropped without a shroud. The fan is able to move air from all around it, which reduces the resistance the fan has to overcome if all/most of the air it draws has to be pulled through all the fins on a rad. I would expect a shrouded fan pulling through a 4-row rad to rob more hp than the same fan with a 3-row rad. More resistance to the cfm it's trying to move. I would also expect a fan fully within a shroud to draw more hp than one half in/half out. It can't cheat by pulling part of its cfm from unrestricted air from outside the shroud. Now cooling efficiency is just the opposite. The more air a fan can (has to) pull through the rad, the better the cooling. But that cooling efficiency comes at the cost of hp. The trick is to find the sweet spot where you pull just enough air through the rad in an efficient manner to cool the engine to the target temp. A 4-row rad with a loose fitting, or no shroud and a 16" fan might get the engine temp where you want it. But, maybe the best combo is a fully shrouded 3-row fan with a fully inserted 10" fan. The tight shroud ensures that nearly all of the fan's cfm moves through the rad so none is wasted by pulling air from behind the rad, and the smaller fan required to accomplish that takes less hp to drive. Win-win. Of course the amount of testing required to find that sweet spot, and factor in the effect of additional forced airflow through the rad as the car speed increases, would be mind-boggling.Groover wrote:Can we assume that the HP gained/or lost is proportional to the engine displacement/HP?
That is to say that while this costs or saves 30 hp on a 350 chevy, it would cost or save proportionally less on a 260 SBF.
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Jim