Here is some basic PCV and crankcase evacuation 101, and reading this there is plenty of good info, and the usual misudnerstandings of all the functions of the PCV system (Positive Crankcase Evacuation)
First and most common mistaken assumption is that the PCV system is primarily there to relieve pressure from the crankcase, and that is only one function. The most important is to constantly remove the damaging compounds that are combustion by-products and enter as blow-by. If these are not immediately evacuated, or "suck out and flushed out" of the crankcase while still in a suspended or gaseous state, quickly settle into the oil and contaminate the oil reducing it's ability to protect. Once these compounds settle into the crankcase and oil, it is difficult to remove them. And they consist of this:
Water, released during the intense heat and pressure of the combustion process.
Un-burnt fuel, no fuel in an internal combustion engine burns completely.
Sulfuric Acid, forms when the different compounds mix as they enter.
Abrasive carbon and soot particles.
And other hydrocarbon related compounds.
This training video covers a naturally aspirated engine and how, and why the PCV system is critical to all engines for long life:
If all you do is relieve pressure, then almost all of these nasty compounds remain in the crankcase increasing wear of the internal parts and contaminating the oil so it cannot protect properly.
On race engines, we always use a belt driven vacuum pump (the best possible solution) to assure not only immediate evacuation of these compounds, but we also maintain vacuum on the crankcase to facilitate ring seal (this allows us to run a low tension ring for less friction and parasitic loss) and to add power from eliminating most downward windage pressure on the pistons. Here is a good video of Matt Scranton (have raced w/Scranton Bro's for ages) showing this:
Now, if you eliminate the evacuation suction, all this damaging gunk is remaining in, and accumulating in the crankcase (as the EcoBoost has such a severe issue with). So, venting can only work if your changing oil every week or so depending on the mileage driven, and that is an error so many make as proper PCV system function is not taught to techs anymore, and only us old timers that grew up when it was understand, or in the racing industry it is passed down to some. Far to often we see evac systems disabled and breathers run that only release pressure, and defeat all the other critical functions of the PCV system.
So, on a Naturally Aspirated engine, intake manifold provides this evacuation suction....but with a turbo application, the intake manifold will not provide suction anytime the engine is under acceleration, highway cruise, etc. So ONLY when at idle, deceleration, or very lite throttle is there sufficient vacuum to evacuate (at under 2-3", evacuation halts and the PCV valve in the passenger side valve cover, the "foul" or "dirty" side, so no evacuation can take place. So, as Ford management decided to save money by utilizing a PCV system that can only work properly on a non-turbo engine, most of the time no evacuation takes place, and the crankcase pressure builds until seeking the path of least resistance back-flows out the cleanside inlet into the driverside turbo inlet (cleanside should NEVER flow backwards or you are defeating the principals of evacuation) pushing this concentrated mix of gunk into the inlet tube where the turbo sucks it and pushes it into the CAC (intercooler), where it condenses and accumulates to later be ingested when under heavy acceleration/full boost blowing out spark at the least (causes shudder and misfire and poor fuel economy as this is contaminating the A/F mixture so detonation occurs and the ECU pulls timing as well as less energy is released per explosive event if anything by air & fuel is present.
If more than a tablespoon or so is pushed into a combustion chamber, liquid does not compress, so pistons break, rods bend/break, and catastrophic engine failure results (see NTSB investigation).
So, the RX system was designed (until copied, was the ONLY system that utilized both IM vac and turbo suction to maintain constant evacuation) to use intake manifold vacuum to evacuate when in non-boost, and turbo suction to continue evacuation when in-boost so no matter what, the crankcase is being evacuated. Clean, filtered fresh air enters the drivers side valve/cam cover from the airbox, replaces the foul/dirty vapors being sucked out the passenger side, and uses one-way checkvalves to ensure no boost pressure can enter the crankcase and maintain a constant evacuation of this "gunk".
Let me know if there are other questions, please ask so I can clarify anything confusing. The PCV system is the most misunderstood of any system on modern cars and light trucks, and very few from dealer techs to racers and performance shops understand it. It used to be part of every automotive techs training, but for the past 20 plus years has been ignored, and now with todays direct injection engines, this is more critical than ever.
