Catch tank with or without PCV??????
 

This image looks to me like the PCV valve has been removed & a single pipe has been run from the crankcase breather (centre/left of the block) to the inlet manifold (via the catch can).

So if the PCV valve closes under boost so any crankcase pressure / blow by is diverted directly into the inlet manifold (manifold port will be blocked off in the above image).

So without the PCV valve all crankcase pressure will be sent via the breather to the catch can whether the car is on or off boost. (I assume this is why when people plumb the catch can in after the PCV & leave the manifold pipe connected the catch can doesn't collect anything as all the blow by is forced into the inlet manifold under boost).

https://cimg5.ibsrv.net/gimg/www.sco...5e0864589f.png



However this drawing (which I am lead to believe is supplied with the RCM catch can) says "block off the smaller of the two outlets on the PCV valve". Which insinuates the PCV valve is left connected & is plumbed into the catch can, however with pipe to the inlet manifold blanked off :confused:

https://cimg0.ibsrv.net/gimg/www.sco...1945e07707.png



Surely if that's correct then no crankcase pressure can escape under boost as the PCV valve will be shut (sounds dangerous)? So either these two images contradict each other or that 90 degree piece from the crank case breather in the first image has a PCV valve in it?


Whilst typing this I am in no doubt you should ditch the PCV & block off the port on the inlet manifold so pressure can escape 100% of the time & all is caught via the catch can so am I reading the last image wrong or missing something?

Sorry if this is confusing :wonder:

i plumbed mine with the pcv still in place and it’s been fine

But with the PCV valve still in place when the car’s under boost it shuts & all the crankcase pressure goes directly into your inlet manifold.

Your catch can will only pick up crankcase vapour etc when the PCV valve is open (the car’s not on boost) which isn’t where most of the blow by etc will happen.

That how I currently understand how it works :wonder:

i understand what you are saying , i think if the pcv was supposed to be open on boost then subaru would design it that way , i think if it was open on boost it would produce a lot more than a catch can could cope with , in theory once off boost what ever is floating around will dealt with by the catch can , my engine was a fairly recent build and catches very little , or was put on due to a smoke issue on the rebuild till the engine bedded in

My understanding is the PCV valve is a small bore non return valve. It allows crank case fumes into the inlet manifold when it's off boost. When on boost, it must close to prevent crankcase pressurisation. I assume it's small bore or otherwise limits crankcase suction to prevent excess oil draw off and mixture weakening.
I've just fitted a Grimmspeed separator. It collects from the 2 pipes that vent into turbo inlet duct. I've left my pcv valve in place. Can't comment on how it works yet. It's only done 15 miles 😊. It seems to run ok so far.

Seems like on the RCM diagrams the PCV valvehas definitely been removed then as there would be no way to leave it in place while blanking off the port (that closes under boost) to the inlet manifold).

When you could but it would end in tears.

I am going to remove the PCV valve & plumb the crankcase & cylinder head breathers into my can on a closed loop so there’s a return to the inlet manifold & metered air that’s in the system isn’t lost.

Then before mapping I’ll vent the can to atmosphere, & have the fueling tuned based on how the car’s actually running (on clean & fresh air only from the inlet with no recirculation from the engine breathers.

There’s also the option to fit a threaded barb instead of the drain plug & run line to return the oil to sump making it a stand alone system :wonder:

If you do that, plug the connection to in inlet duct to ensure that all the air into the engine is metered.

Yes mate, bungs with ridges on available on eBay to jubilee clip into the holes :thumb: