re:  You can force a lot of air into a cavity but it's just as
important to remove it as quickly as it goes in, otherwise it becomes
dormant (useless)

More than useless, aero drag occurs, defeating the purpose.

The analogy is the same as the aero drag on the body, i.e., the faster
you go, more power is required to overcome drag.  Accelerating air
through the engine compartment creates more drag and there is just no
way any performance component is enhanced.  The only way to enhance
performance with more airflow via "scoops" is to pressurize the engine
intake as in supercharging, and that won't happen unless the
connection is direct.

Also, on an aircooled it's difficult to believe the fan is
"cavitating" and not getting enough air.  It's also hard to believe
pressurizing air against the cooling fan is not going to be power
robbing.  It's not even free to just go to a lower altitude. And why
is it needed, anyway?  On wasserboxers, it's all irrelevant because
cooling occurs at the front.  On the oil cooler, the thermostat will
just adjust to maintain the same temperature--cooler temp reduces
performance anyway.  These engines do not overheat given integrity of
cooling system components.  If you want your engine to run cooler (and
it's water cooled) you'll achieve more much easier with just a cooler
thermostat.  On air cooled, choices may be limited to increasing oil
sump capacity.  In any event, what you'll achieve is reduced
performance and increased fuel consumption.  Said yet another way and
another time, you do not want your engine to run cooler, you want it
to run at design temperature.

Discussion of "scoops" on Vanagons is pointless except as discussion
of cosmetics and to learn it's net negative as regards performance.

TANSTAAFL