PCV Question

[HOSTILETAKEOVER]

Geoff: I don't know if this will answer your questions and I'm not certain that it is the same for all LS engines, but this is from the GMPP documentation for my LSX 454 (I added the highlight):



Positive Crankcase Ventilation System (PCV)
How the PVC system works:
A closed crankcase ventilation system should be used in order to provide a more complete scavenging of crankcase vapors. Filtered air
from the air induction system (air cleaner) duct is supplied to the crankcase, mixed with blow-by vapors, and passes through a crankcase
ventilation metering device before entering the intake manifold. The primary component in the positive crankcase ventilation (PCV) system
is the PCV flow metering orifice. Vacuum changes within the intake manifold result in flow variations of the blow-by vapors. If abnormal
operating conditions occur, the design of the PCV system permits excessive amounts of blow-by vapors to back flow through the crankcase
vent tube and into the engine induction system (air cleaner) to be consumed during normal combustion. This engine ventilation system
design minimizes oil consumption and significantly reduces the potential for oil ingestion during vehicle limit handling maneuvers.
How to set up your PVC system:
• There are three ports on the LSX long block that make up the PCV system. There are two foul side ports. Both of these ports should be
connected to the intake manifold and be exposed to vacuum at idle.
• The two ports are 1) Front port on the valley cover. 2) Left rear (driver) valve cover. These two silver tubes may look simple but, they should
not be modified. Both of the tubes have a small orifice within them that, is used in place of a PCV valve of early designs.
• There is one fresh air port which is on the front of the right (passenger) valve cover. Again this is a silver tube that faces forward on the valve
cover. This port should be connected to filtered clean air. This is typically within the engines air cleaner system or can be a separate air
filter if using a carburetor. If you are planning on an electronic fuel injections system that uses a mass air flow meter (MAF) then, the fresh
air to the PCV should be installed between the MAF and engine’s throttle body. The engine burns the air that enters the PCV system so,
if the fresh air port is prior to the MAF then, this air will enter the engine without being measured by the MAF.

Im a little confused. I would expect that all three tubes (driver valve cover, pass valve cover and valley cover) should all be routed to the air intake just prior or after the throttle body. Any air pressure that needs to be vented from the crankcase would be as a result of blowby and pumping action of the pistons moving up and down???

Update:

After much web surfing, reading and a few phone calls, I have it figured out. There needs to be fresh air in and dirty air out so acids etc... dont build up in the crank case.

In order to do this there needs to be a pressure difference and that is provided by having fresh air (passenger valve cover) come in from somwhere in front of the throttle body (a slight vacum) and dirty air (driver side valve cover and if your motor has it the lifter valley cover) being pulled out from somewhere behind the throttle boday (much higher vacum)

That is a very simplified but practical answer. Depending what year your LS motor is will determine if you need a PCV valve inline.

Norris Motorsports has some info about what year motors need a sepperate PCV valve on his website. He was also very helpful on the phone!