70% of the contents of blow by gases is unburned fuel not oil
The PCV valve runs from the backside of the engine to the intake manifold and this is the system that IS under vacuum
The tube running from the front of the engine to the intake is the breather tube this tube is not under vacuum.
80-90% of all blow by gas is routed to through the PCV valve to the intake manifold. This is where you will collect the most amount of oil, unburned fuel and water vapor in a catch can.
The breather tube is for excess blow by not routed through PCV only under high load, namely in forced induction.
If you are NOT running forced induction, running a catch can on the breather tube is basically useless.
Blow by gases increase in a linear fashion based on engine load. (Lower Load = Less | Higher Load = More)
If you drive for efficiency (low engine load) blow by will be minimal and thus a catch can on either the PCV line or breather line would catch little to nothing.
PCV Systems including vacuum are integral part of engine design and included in air to fuel ratio computation by ECU/ECM.
CATCH CAN SYSTEMS:
OPEN SYSTEMS:
Cans that do not route PCV gas back into the intake manifold.
Anti-lag has a specifically designed open catch can for turbo setups which benefit from having an open system. It is perfect for those who do not want any type of oil or blow by gases back in the intercooler or intake.
However depending where you life you may fail emissions inspection if they find you are venting PCV gases into the atmosphere.
CLOSED SYSTEMS:
Radium, and several others provide systems that sit in between the PCV valve and the intake manifold or in between the breather line and intake.
These systems hooked up correctly, do NOT bypass the PCV system, they run inline. However the cans must be drained periodically to prevent over flow or plugging the PCV system.
Basically this covers the Crawford Can, it sits between the PCV and the breather tube, and separates the air and oil back into the block. The concept is you put the blow by gas and oil back into the engine without having to drain a can. The problem not even addressed by Crawford is, blow by gas is oil, fuel and vapor that is blown by passed the rings thus contaminated. In a true performance setup do you want contaminated oil back into the block?
DIFFERENCES IN CANS:
Baffled or Condensors
Cans that use condensers or baffles help to take the blow by gas and help condense oil and prevent it from just flowing right back out of the can into the intake manifold or intake.
Cans with a straight open design with an inlet and outlet port.
These cans are basically the cheapest and least effective at trapping/separating oil, fuel and moisture. Without a baffle system there is nothing to help separate the oil from the air.
AOS
Air oil separators that use special channels to help separate the incoming air vapor into "clean" vapor and oil back into the block/oil?
