I'm assuming this is for an FC.
Is this purely a "crankcase" evac system?
Since I didn't read anything about the gas tank vapor purge, I'll assume this is not part of your system...
I like the idea of running the crankcase with some vacuum.
Having the crankcase pressurized could possibly hurt power and / or cause headaches like smoking turbos.
The hard part is...how do you do it?
The stock system is overly complicated.
Mazda's stupid "purge valve" is another one of those engineering-bragging doohickeys that makes things a headache.
When we run race cars on the track, we 1) cap the bottom nipple on the center iron, and 2) run a single vent off the top of the oil filler neck.
Whether you want to run it as a recovery system or a purely purge / vent system is up to you.
Oil *will* creep up the oil filler neck to easily spew out the lower fitting in the center iron when you toss the car around the track.
Even with oil baffle pans, you can still get oil puking out that lower fitting.
We've never had too much problems with oil puking out the top of the oil filler neck.
I'm also assuming that this is for a turbo 13B.
This is good and bad.
Running vacuum in the crankcase relieves pressure that would end up puking oil out the piston compressor ring in the turbo turbine.
Effect?
Oil spews out the hot turbine section and burns in the exhaust causing embarassing oil smoke.
Bad?
Push the turbo hard enough and this causes the oil to foam more after the CHRA.
Foaming, hot oil causes more vapor crap, which causes more crap to get puked out the system.
Another bad thing...
With a turbo engine, the only "spot" that has constant vacuum is before the turbo.
If we're talking purely vapor, this would not be a problem.
In reality, we're also ingesting (hopefully) minute amounts of liquid that's hitting a (delicately) spinning compressor wheel.
Mazda decided to do this full-time with their system.
It's probably the best, passive system that could be integrated into engine at that time.
-Ted