Somewhat related to this overall subject, when using an electric fan (puller, 1 or 2 fans), some fan shrouds are solid, while others have small venting slots or flappers around the otherwise solid shroud areas. I'm considering to get an electric fan (1 or 2), that would have a fan shroud. Any preference/suggestion on the design of the shroud? This would be for my aluminum triple-flow US Radiator, 22" wide (fitting my core opening)... runs hot while road racing/autocrossing, but cool in regular street or hwy driving. I've tried different thermostats... no difference when racing.