DeTomaso Mailing List: September 2000, Message #250

A properly installed PCV system actually creates a pressure differential,
as the PCV side is connected to a large manifold vacuum source, typically
underneath the primaries of the carb, and the air source line connected to
the air cleaner, at atmospheric pressure.  Therefore, both sides are NOT
connected to vacuum, as I think the original post was ascertaining.  So a
valve cover filter/cap style cap would perform the same function as running
the hose to the small filter in the air cleaner assembly.  I think it's
just a matter of your choice.  The PCV hose filter in the air cleaner stand
a better chance of staying clean than the filter/cap sitting on the valve
cover.

my 2 cents,

Asa Jay