Your motor has blow-by. In fact, all piston-driven engines do. To combat this, they are designed with a positive crankcase ventilation system (PCV). This links the engine’s crankcase to the intake manifold via a one-way valve and tube. The low pressure in the intake, creates a vacuum that sucks the higher pressure air in the crankcase out and keeps the engine operating at, or near, a vacuum condition.
Truthfully, it is a great concept that removes extra pressure and potentially-harmful atmospheric moisture and fuel vapor from the engine’s innards. For the everyday driver or street enthusiast, the system is nearly infallible. But, if you are racking up miles around the road course or pegging the tachometer at the drag strip, your PCV system will likely start dumping oil directly into your engine — they don’t like that.
Sustained high RPM (or high boost) can contribute to increased blow-by and oil mist in the crankcase. Left unchecked, this oil vapor flows through the PVC system, eventually carrying oil directly into the cylinders.
Also, Oil vapor in the intake is detrimental to performance as it degrades the effective octane rating of fuel and cruds up the plugs and combustion surfaces. For that reason a catch can is necessary in all high performance situations.
An oil catch can, or air/oil separator, uses specially designed baffles and mesh screens to pull the oil vapor out of the crankcase charge. This allows the crankcase pressure to vent cleanly into the engine while keeping the oil out
In the MorosoTV video above, we can clearly see a Moroso Air/Oil Separator doing its job over the course of one spirited trip in a 2009 Cadillac CTS-V. Without the separator, all of that oil would have been swallowed up by the engine.