Just took a standard, empty catch can w/ a looking tube and a drain plug and 2 outlets up top, and cut a hole 1-1/4" OD and put a 3" filter on top to vent it...

Im running my two, factory VC vent ports with a diameter of 3/8" each, one in the front and one in the rear; mind you im a FWD...
but each port has sylicone hose lead that goes into the catch can; catch can has two outlets up top.

I was having trouble with blowing oil out my "factory oil pan leak" if there is such a thing...GM, kind of expected it, but im loosing oil out that pan gasket leak... Did a dye test, and after boosting around town a lil and some everyday driving, got out the florescent and deterimened it wasnt my rear-main; which i discovered had a TSB out on it by the way... but did see the factory leak showing its face like normal in the form of beads off the pan bolts, this time, it had a very little bit of dye that we could see, but no leaks under the car like we had when we would do WOT passes during some of the tuning ...it was puddled pretty good, but nothing here recently after those select runs.

So, we have determined after doing some research and talking to some other boosted front-mount LS4 guys and some other FI guys here, that one, the
LS4 just seems to have a real hard time venting any crankcase pressure and needs as much assistance doing so as possible...we were using the STS PCV switch kit in the beginning, but i wasnt catching any or hardly any blow by in the little gauze on the switch itself...just didnt seem to be large enough to vent anykind of pressure..especially not seeing much oil at all...we decided to to do some changing up and went with the above set up with the catch can...

Now, my question...: With the way I have it right now, do i NEED A VACUUM SOURCE??
The way I have it ran right now, it has no vacuum source...keep in mind that im limited to where i can vent and go on the VC or at the filler neck because I have not only my coil packs in the way, but i have my oil return coming from the oil pump on the filler neck.

Just a tid bit, i was using the factory plastic tabbed nipple connectors originally and was getting all the oil blow by on the top end of the motor, so i have eliminated those and went straight on with all of my connections before i went to the catch can and thats when i started getting oil underneath...so im chasing a gopher in holes right now....but hoping this catch can will solve my crankcase venting issues...so any input would be greatly appreciated...

 

You shouldn't need a vacuum, but IMO 3/8" line is pretty small for venting use on an FI motor. -10 (5/8") lines might help.

Jim