[Idaho2018GTPremium]

GM put engineering effort into minimizing the risk of oil circulation back into the intake manifold:

"One issue that faced engineers was equalizing the pressure across different parts of the crankcase. The Gen 5 block has bulkhead breathing cavities just above the cross-bolts on the nodular-iron main caps to allow air to circulate between cylinder banks, yet that proved to be insufficient on the LT4. Because all oil drainback feeds through the center of the block, differences in crankcase pressure can prevent oil from draining properly, causing the PCV to suck up oil rather than crankcase gases. "It's critical that we get oil out of the valley," says Alan Rice, the design responsible engineer for ventilation and lubrication. The solution was simple: two holes, roughly 58 inch in diameter, were drilled into each lifter valley. A PCV separator, which is unique to the LT4, was developed to keep oily air from being drawn through the intake, where it could end up collecting on the back of the intake valves. A little bit of oil on a port-injected engine can help lubricate valves, but because all Gen 5 V8s are direct injected, there's no fuel washing the back of the intake valve. That means oil in the PCV system can end up sticking to the back of the hot intake valves impeding airflow and eventually preventing the valves from seating properly."

Very interesting article by Hotrod magazine:

https://www.hotrod.com/articles/the-...e-z06s-lt4-v8/