Dave,

The issue of pressure zones is a good one. Some years ago following a
discussion with Dr. Tim, I set up a water manometer the pressure levels at
the top and bottom of the vent chamber. Can't locate the results quickly but
they are probably in the archives under ancient history. As a result of those
measurements, I sealed off the drivers side vent with a viton flap which is
anchored to the top of the engine compartment, the side edge of the defining
wheelwell, and open on the bottom. The viton (from a diving shop) was cut to
be long enough to go to the bottom of the frame rail. Inside this sealed
compartment, I mount my air cleaner (K&N, biggest I could fit) and the air
flow sensor. This was to ensure that the hot engine compartment air would not
be drawn into the intake. Haven't had a problem in years.

Those measurements also showed a high pressure zone in the area of the axle
shafts and above the transmission. This is with the diesel sound shield in
place. This is where I mounted the Mazda RX-7 external air cooler.

But, the area is quite compromised for efficient air to air intercooling. In
my case, I am building a liquid to air intercooler with a continuous duty
Shurflo electric water pump for recirculation, a small radiator in the front
of the vanagon, large diameter heater hose for the routing of coolant and a
golf reservoir mounted above the rear axles. It will be triggered by
temperature and by the manifold pressure switch.

Frank Grunthaner