PCV and Crankcase Evacuation 101
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12-29-2014, 05:32 PM
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PCV and Crankcase Evacuation 101
PCV and crankcase evacuation 101
Here is basic PCV and crankcase evacuation info, there is plenty of good info, along with the usual misunderstandings of PCV system (Positive Crankcase Evacuation) functionality.
First, the most common assumption made is that the PCV system is primarily there to relieve pressure from the crankcase, but that’s only one function. The most important is to constantly remove the damaging compounds, combustion by-products that enter as blow-by. If these are not immediately evacuated, or "sucked out and flushed out" of the crankcase while still in a suspended or gaseous state they quickly settle into the oil, contaminating the oil thus reducing its ability to provide protection. Once these compounds settle into the crankcase and oil, it is difficult to remove them. They consist of the following:
Water (released during the intense heat and pressure of the combustion process.)
Un-burned fuel (no fuel in an internal combustion engine burns completely.)
Sulfuric Acid (This forms when the different compounds mix as they enter.)
Abrasive carbon and soot particles.
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 air 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 you’re changing oil every week or so depending on the mileage driven, and that is an error so many make. Proper PCV system function is not taught to techs anymore, and only understood by us old timers or those in the racing industry that have passed it down. Far too often we see evacuation systems disabled and breathers that only release pressure, defeating all the other critical functions of the PCV system.
So, on a Naturally Aspirated engine the intake manifold provides the evacuation suction. In a turbo application, the intake manifold does not provide suction when the engine is under acceleration, highway cruise, etc. but ONLY when at idle, deceleration or very lite throttle. Under 2-3 lbs. of boost evacuation halts and the PCV valve in the passenger side valve cover ("foul" or "dirty" side) closes so no evacuation can take place. 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 little to no evacuation takes place, and the crankcase pressure builds until seeking the path of least resistance. It then back-flows out the clean side inlet into the driver side turbo inlet (clean side should never flow backwards or you are defeating the principals of evacuation) pushing this concentrated mix of gunk into the inlet tube. The turbo inhales it and pushes it into the CAC (intercooler), where it condenses and accumulates to later be ingested. When under heavy acceleration (full boost) spark is extinguished, at the least causing shudder, misfire and diminishing fuel economy. This contaminates the air/fuel mixture at detonation causing the ECU to pull timing. Energy is released per explosive event if anything but air & fuel is present.
If more than a tablespoon of water is pushed into the combustion chamber, pistons may break, rods bend/break, and catastrophic engine failure results. Liquid doesn’t compress. (See NTSB investigation).
The RX system is designed to utilize both intake manifold and turbo vacuum to maintain constant evacuation and intake manifold vacuum to evacuate when in non-boost. Turbo inhalation is utilized to continue evacuation when in-boost for constant crankcase evacuation. Clean/filtered fresh air enters the driver’s side valve cover from the air box replacing the foul/dirty vapors being removed from the passenger side valve cover. The system uses one-way check valves to ensure no boost pressure can enter the crankcase and maintain a constant evacuation of any contaminated vapors.
If there are any questions that arise from the read please let me know so I can clarify any confusion. The PCV system is the most misunderstood of any system on modern cars and light trucks, and very few dealer techs, racers and performance shops understand it. It used to be part of every automotive techs training, but for the past 20 plus years this has been ignored. This training with today’s direct injection engines, is more critical than ever.
Here is basic PCV and crankcase evacuation info, there is plenty of good info, along with the usual misunderstandings of PCV system (Positive Crankcase Evacuation) functionality.
First, the most common assumption made is that the PCV system is primarily there to relieve pressure from the crankcase, but that’s only one function. The most important is to constantly remove the damaging compounds, combustion by-products that enter as blow-by. If these are not immediately evacuated, or "sucked out and flushed out" of the crankcase while still in a suspended or gaseous state they quickly settle into the oil, contaminating the oil thus reducing its ability to provide protection. Once these compounds settle into the crankcase and oil, it is difficult to remove them. They consist of the following:
Water (released during the intense heat and pressure of the combustion process.)
Un-burned fuel (no fuel in an internal combustion engine burns completely.)
Sulfuric Acid (This forms when the different compounds mix as they enter.)
Abrasive carbon and soot particles.
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 air 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 you’re changing oil every week or so depending on the mileage driven, and that is an error so many make. Proper PCV system function is not taught to techs anymore, and only understood by us old timers or those in the racing industry that have passed it down. Far too often we see evacuation systems disabled and breathers that only release pressure, defeating all the other critical functions of the PCV system.
So, on a Naturally Aspirated engine the intake manifold provides the evacuation suction. In a turbo application, the intake manifold does not provide suction when the engine is under acceleration, highway cruise, etc. but ONLY when at idle, deceleration or very lite throttle. Under 2-3 lbs. of boost evacuation halts and the PCV valve in the passenger side valve cover ("foul" or "dirty" side) closes so no evacuation can take place. 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 little to no evacuation takes place, and the crankcase pressure builds until seeking the path of least resistance. It then back-flows out the clean side inlet into the driver side turbo inlet (clean side should never flow backwards or you are defeating the principals of evacuation) pushing this concentrated mix of gunk into the inlet tube. The turbo inhales it and pushes it into the CAC (intercooler), where it condenses and accumulates to later be ingested. When under heavy acceleration (full boost) spark is extinguished, at the least causing shudder, misfire and diminishing fuel economy. This contaminates the air/fuel mixture at detonation causing the ECU to pull timing. Energy is released per explosive event if anything but air & fuel is present.
If more than a tablespoon of water is pushed into the combustion chamber, pistons may break, rods bend/break, and catastrophic engine failure results. Liquid doesn’t compress. (See NTSB investigation).
The RX system is designed to utilize both intake manifold and turbo vacuum to maintain constant evacuation and intake manifold vacuum to evacuate when in non-boost. Turbo inhalation is utilized to continue evacuation when in-boost for constant crankcase evacuation. Clean/filtered fresh air enters the driver’s side valve cover from the air box replacing the foul/dirty vapors being removed from the passenger side valve cover. The system uses one-way check valves to ensure no boost pressure can enter the crankcase and maintain a constant evacuation of any contaminated vapors.
If there are any questions that arise from the read please let me know so I can clarify any confusion. The PCV system is the most misunderstood of any system on modern cars and light trucks, and very few dealer techs, racers and performance shops understand it. It used to be part of every automotive techs training, but for the past 20 plus years this has been ignored. This training with today’s direct injection engines, is more critical than ever.