Hey again RD. I believe there often IS a pressure drop at the breather connection to the incoming air stream. I have seen some slight oil aspiration at this nipple after the PCV hose mod, esp on engines where the nipple is close to the TB on the air duct.
Remember when this mod is done the PCV system changes from flow-through circulation due to manifold vacuum, into ventilation of the crankcase into incoming filtered airstream. At idle/low engine rpm/load less blowby is created. Higher RPM/loads cause more blowby. Airflow into engine follows right with RPM/load.
This is all my opinion, I'm not an engineer or engine designer, but I think I'm right about all this.
I've learned that in Carburetors, there is reference to 3 types of vacuum: Manifold, Ported and Venturi. Refers to where a vacuum hose port/connection/nipple is located and under what conditions a pressure drop (vacuum) will occur at such point.
Manifold: connected into intake manifold direct, below throttle plate, vacuum always present if engine is running.
Ported: mostly only on Carbs. A nipple positioned on Carb throttle body base such that at idle the port is above throttle plate,(no vacuum). As throttle opens the port is exposed to manifold vac. This allows a vacuum signal to be timed, off and on, usually for distributor vacuum advance on such older engines.
Venturi: the nipple connects into carb bore, but higher above throttle plate often in main body casting of carb. As throttle opens up airflow increases in the bore and at a certain point the Venturi effect occurs at this port, namely: as flow increases so does airspeed. Increasing air SPEED causes air pressure this port is exposed to to drop somewhat. This vacuum signal is/was used often for control of emission control devices like EGR.
Sorry for all that, RD! Reason for it is to explain my ideas of how/why a modest pressure drop can occur at the breather nipple in the air duct--it gets Venturi Vacuum applied to it with increased engine RPM/load. Plus with higher RPM/load we get more blowby, increasing crankcase pressure/gas volume. Crankcase pressure is vented into incoming airstream and exposed to a moderately lower pressure. So we are still Positively Ventilating the Crankcase (in my opinion)
And yes by teeing the 2 hoses together into the breather nipple on air duct both will be ventilating as I describe, though many PCV Valves have a tapered needle valve that can open/close under different conditions.
you asked good questions, RD!! Hope your eyes don't hurt too much...
TracyG Gadgetman Reno