i run twin fans on my radiator and don't use a shroud. as long as the fans are mounted close enough to the radiator, you don't need a shroud. and in that case if its not designed well, it could actually hurt cooling at higher speeds. I've seen some shrouds build with door or louvers that open when at speed. seems like kind of a hokey fix. I've never had my engine overheat and can watch the temp gauge drop when the fans are on.