[usinjin]

I've been having issues with my boosted setup for a while and am still in the process of figuring out exactly where the problem lies. It's an AA stage 1 setup. Moderate throttle is causing bucking. My inclination is that there's a vacuum/boost leak somewhere.

At any rate, that's not really what my question is about here. I wanted to switch over to the M56 CCV system to see if that helped, so I have bypass the stock CCV and rebuilt the CCV in the M56 vc with a new diaphragm and the really nice billet aluminum cap. The vc is now run directly into the crankcase vacuum rail.

The car does seem to breathe/run more smoothly, and the boost definitely builds more smoothly and linearly too. Before I'd really have to stomp on the throttle to see the vacuum decrease at all. However, it is pushing oil out of the vc gasket. I've already replaced the gasket (albeit a while ago) and was thinking I'd just replace it again..except I noticed that oil is being pushed out of the oil cap, too. The cap has also been replaced at some point.

Is the pressure in the crankcase too high? Do I need to install an additional PCV somewhere? Maybe my vc needs to be resurfaced? Any advice would be hugely appreciated. Thanks!

 

[Psimitar]

When you go boosted then anything to do with the crank ventilation system needs to be plumbed into before the turbo inlet side of the intake tubing. You may also require an upgraded one way valve for the brake booster vac line to ensure the vac can never sees boost.

 

[M.Blacktree]

I'm not sure what is this crankcase vacuum rail. Are you talking about the vacuum distribution rail on the intake manifold? That gets pressurized under boost. So it's putting boost pressure into the crankcase. Not good. The CCV needs to be connected to something that does not see boost pressure, or just vented to atmosphere.

 

[Psimitar]

I would suggest you use RealOEM website to look at the diagrams for the CCV to get an idea of how the CCV works aswell as some google searching and learning.

Basically a normally aspirated engine creates a vacuum in the inlet manifold to suck air in to mix with fuel. The pistons create positive pressure in the crankcase and before emissions standards this just vented to atmosphere but now the pressure is released via the CCV and the oil mist and blowby gasses get fed into the inlet manifold to be burnt by the combustion cycle of the engine.

When you fit a turbo then aside for very low revs the inlet manifold is now positively pressurised and hence the crankcase ventilation system has nowhere for it to go but worse can become more pressurised by the turbo boost pressure.

So the CCV system needs to be plumbed before the turbo so that it is seeing a vacuum once more.