The reason people are reluctant to air cooled is the "ustad syndrome" in Pakistan - most of these guys do not know jack about their own trade - e.g. they refuse to believe that air takes the path of least resistance and scoff on little items like the air shroud rubber seal - if that is not in place - instead of fresh (cool) air being sucked from the lid and louvres - the fan will simply recycle the air that is already there.
In a bus - the engine room actually is filled with a lot of cool air as the bus drives down the road - the fans job is to push the air on to the cooling fins and oil cooler to cool the engine down.
If you think air cooled flat 4 average compression engine sounds a bit risky - how does a porsche flat 6 with turbocharger sound to you? Its also air cooled and it can teach most cars a lesson on not to mess with it. It can sustain extreme speeds for hours. Yet its missing one big component - the coolant radiator.
In an aircooled engine - the ambient air is the coolant. You have tons of it for free available at all times, its how you want to use it. If you are into data networks and have to document a plan to reduce energy costs of a data centre - you will know how crucial air channeling is.
a VW beetle/bus/ghia/passat etc engine room is just like that.
