PCV Perceptions
PCV is an acronym for Positive Crankcase Ventilation. Gasoline engines have a PCV valve that connects the crankcase to the intake manifold, which allows crankcase gasses to be recirculated back into the intake air charge where they are burned in the combustion process. Diesel engines sometimes simply vent the crankcase to atmosphere (older versions), or incorporate a CCV (CrankCase Ventilation) system that filters the gasses, then pipes them to the air intake. The first PCV Valve was introduced in the 1964 model year on gasoline engines. Prior to that, even gas engines simply “dumped” crankcase gasses to atmosphere through a draft tube. Diesel engines started seeing some form of crankcase gas recirculation in the 1990’s, with full mandated implementation in the 2010's. The delay is because the crankcase gasses from a diesel engine are so incredibly toxic, that directly recirculating them would kill the engine in extremely short order! It took 3 more decades to find a way to make it work.
PCV Catch Can
There are contaminants in gasoline engine crankcase gasses as well; oils, water, and acids. An inexpensive “Catch Can” filters out many of these harmful liquids, and passes the light vapors to the air intake. This is basically how a diesel CCV system works. The Can does fill up with these trapped contaminants, though. When you change your oil, empty the Can. A more labor-intensive alternative is to route a drain hose back to the oil pan. You can also combine a PCV Catch Can with Water Vapor Injection (see Expounding on Expansion).
No matter what technology you look at, energy is harvested when there is a differential in “pressure”. This can be literal pressure, voltage, temperature, or other energy type. In an engine, the cylinder draws in an air/fuel charge, compresses it, then ignites it. The pressure on the top of the piston (inside the combustion chamber) created by the burning fuel is higher than the bottom of the piston (the crankcase). To make more power, you can increase the pressure on the top side of the piston, or reduce the pressure (maybe even create a vacuum) on the bottom side of the piston. Both increase the differential, thus power output.
This strongly suggests that it might just be advantageous to create a vacuum in the crankcase!?! Diesel engines don’t generate any usable vacuum, but gas engines certainly do. What would a vacuum on the crankcase do for an engine? Well, for starters, if you have a leaky rear main seal, you would suck minute amounts of air in at the seal instead of dumping minute amounts of oil out. So far, this is sounding good. Furthermore, a vacuum on the crankcase means a lower “pressure” on the bottom side of the piston, which makes the positive pressure on the top side more powerful -- a larger “Delta”. This equates to more power at light to medium throttle angle. This would be a good thing also!!
En-Valve
If a little is good, more must be better; is there any such thing as “too much”? Oh yes there is! If you have a marginal gasket or seal, and you apply a massive pressure differential (put a strong vacuum on the crankcase), you could actually “suck in” the little bit of seal or gasket that is “sort of working”. This may increase overall oil consumption.
The late Ron “The Gadgetman” Hatton advocated plugging the crankcase-to-air cleaner hose (the fresh air secondary side) to put a vacuum on the crankcase. This puts full manifold vacuum on the crankcase. I evaluated something called The En-Valve back in the 1990s that put a 5” regulated vacuum on the crankcase. I also tested an adjustable vacuum regulator from McMaster-Carr mounted in the PCV fresh air side to maintain a constant crankcase vacuum. What I found is that with a relatively fresh engine, I couldn’t put too much vacuum on the crankcase. With a tired and worn engine, excessive vacuum would “suck in” gaskets and seals making them leak worse — when the engine was off. Since the factory PCV system contributes air to the intake charge, I also found that constricting the PCV system altered idle speed in some cases (reduced RPM). You can measure crankcase vacuum by putting a vacuum gauge on the dipstick tube. If adjustable, around 5” of vacuum (around 830 kPa) is a safe target.
Adjustable Vacuum Valve
Even with a Catch Can, there are still compounds in PCV gasses that detract from combustion — cost you power and economy. I don’t advocate dumping the crankcase gasses to atmosphere (that would be illegal), but the Smart Emissions Reducer can catalytically break down these heavy elements into lighter, easier to burn gasses. It simply mounts inline in your PCV vacuum hose.
Smart Emissions Reducer
FE2 or FE3 Depending
MPGenie Basics 051 Training - PCV Perceptions
