I have a 427ci LS engine (dart block) and I have proform valve covers. they come pre installed with 90 degree 3/8" barbed fittings for breather hose.... Currently they are not routed anywhere and I am paying the price with oil seepage. I thought that they crankcase would vent on its own without vacuum from the intake. I am obviously wrong.

I plan on running a Moroso catch can where the valve covers run to a Tee which then runs to the CC. From there, I'd run a 10an hose to the intake manifold. BTW, I am running a Holley Mid Rise intake with a 4150 Wilson Manifolds TB.

I was also contemplating doing the above mentioned, but also adding a 10an 1/2 NPT fitting to the valley cover towards the rear of the engine. From there, I'd run a 10an hose to the catch can. (I would opt for a Moroso can that has 2 10an inlets and a 10an fitting on top to run to the intake manifold) From the catch can to the intake would be a 10an hose.

Or I can run a breather on top of the catch can for a free air vent....

I would like feedback on this. Some say the crank case needs vacuum from the engine to assisted with evacuating the crank case.... Others say free air is enough.. Here are some crudely drawn diagrams of what I was thinking about doing.

The line that runs from the top of the catch can feeds into the intake on this one... not the valley cover.. i didn't use a different color to illustrate that

the red line goes to the intake.

 

I basically have the catch can in its own circuit like stock goes from the manifold to valley pan with CC in between. You need to look at it as two separate functions 1) a PCV system that clears the crankcase stuff out and 2) a WOT engine venting when the engine blow by in the crankcase is like 15-20 cfm on a 700 hp naturally asperated motor (because of restriction the PCV system only handles like less than 1 cfm during this WOT period). Then I have a #10 line in valve cover going to a separate catch can that then goes to the front of the TB for the venting. At idle it will suck air from the air intake and makes its way to the engine and then to the PCV. The PCV in the valley cover is a fixed orifice of .100 inches and at best maybe flows 2 cfm at 17 inches of vacuum. Make sure that your dirty side has a restriction in it or your catch can will fill very quickly as a 3/8 hose will draw a lot more air and oil in. So if your PCV is coming from one of the valve covers you need a valve or a restrictor (if you only use 1 valve cover for PCV if not the restrictor needs to be in front of the vacuum source or your can will fill with oil quickly (without restrictor it will flow like 15 cfm). For PCV to work it needs a vacuum source from inside the manifold the vent stuff is not a enough. The PCV only flows like 2-3 cfm with restrictor but it is enough to clear the gases out of the crankcase. The old cars just vented from the valve cover (usually 5/8 to 3/4 inch hose) to the atmosphere via the air cleaner, they had a PCV valve as the restrictor in the valve cover. As far as WOT venting the tight 90 degree 3/8 OD VC hose tubes are kind of restrictive so good you put a 10AN vent tube (pull a VC off and put a 3/8 tube on it and blow through it then pull hose off and just blow through the hose you will feel the difference). One thing I learned if you run a long length of hose it needs to be big to offset the length. Here is a photo of mine and the valley pan restrictor tube that I pulled out.

 

On these proform valve covers, the driver side VC vent tube has a built in restrictor.. like a .125” hole… the passenger side VC has no restrictor in the vent tube.

so if I understand you correctly I should route the driver side vent tube to the intake for vacuum. I can run the passenger side tube around the engine (longer hose adds a restriction in flow) to the intake.

then for High RPM venting, vent the valley pan with a -10an bung with a hose that runs to atmosphere or the intake as well?

 

Yes VC restrictor tube (drivers side) to the intake manifold (vacuum source). Yes the other tube on passenger side can go to the air bridge. I would normally put in the air cleaner but with todays cars the MAF is up there and would get all oily over time. Yes the on the number 10AN to the air bridge (not intake manifold) or the atmosphere. The air bridge and/or air filter area are not considered vacuum sources. At WOT the engine will ingests this air if in air bridge or not if you run to atmosphere. Only the drivers side VC can go to a vacuum source inside the intake manifold (as it is restricted). The reason I run the catch can on the 10AN line WOT vent line is to limit the amount of oil that may get sucked in at WOT. I could also cap my air bridge and run a breather to the atmosphere instead.

 

Ive tried all sorts of different ways to route the pcv system. The one that is by far the best is
clean air in 12an from behind filter air intake to drivers side head
16an from oil fill to catch can, catch can has one way breather on top,
pcv on catch can to intake manifolld
cap off valley cover port

This way the pcv system works like stock when just cruising but at wot it vents to atmosphere