How to Build a Functional PCV System in Performance Engines

Positive Crankcase Ventilation is a phrase that appears to be derogatory, but is it really necessary for others to view it in that manner?

Generally speaking, the PCV system serves two primary purposes, which are the alleviation of vapor and the separation of liquids.

In addition to being among the early pollution controls that were placed on our engines, PCV systems have the potential to drastically cut down on the emissions of hydrocarbons.

How to Build a Functional PCV System in Performance Engines

When it comes to high-performance engines, they also serve a few more very beneficial reasons that are crucial for optimizing power while also being quite useful.

First things first: before we go into the plumbing, let’s go over what’s within the crankcase and how it got there.

It should come as no surprise that the engine contains oil, which is composed of hydrocarbons that have the ability to evaporate and escape.

Instead of generating pollution to the outside world or dosing down the high-octane gasoline in the intake system, this oil should remain in the crankcase, where it can safely lubricate the engine.

It is not difficult for contemporary high-performance engines to surpass the typical operating cylinder pressures of 100 bar that are generated by combustion.

Given that there is no such thing as a perfect seal at the piston rings, it is inevitable that a certain quantity of combustion gasses will be forced into the crankcase when we increase the cylinder pressure while the engine is operating under power.

Even an engine that has just been machined will have leakage rates of between three and five percent, and this percentage will get into the double digits as the engine becomes older. Depending on the type of new V-8 engine, this can range anywhere from 10 to 15 cfm from blowby.

These gasses include a great deal of foreign substances that have the potential to damage the quality of our oil and seals.

It is also possible for some gasoline to get through the more lax tolerances during a cold start, before the engine has had a chance to warm up.

Evaporative emissions can be increased by this surplus fuel, sometimes known as “lost” fuel, which can dilute the oil. It is fortunate that this gasoline typically evaporates as the engine heats up, and thus, it is drawn through the engine together with the other vapors.

Moreover, a significant amount of water is introduced into the system in the form of vapor, either by the flow of air or through the blow-by of exhaust.

This water has the potential to condense inside of a cold engine, where it can combine with other harmful chemicals to produce acids that, over time, have a detrimental effect on the durability of components.

It is possible for the majority of the harmful substances to be taken out as a gas through the PCV system because the factory’s PCV and cooling systems work together to allow the crankcase to warm up to a temperature that is higher than the boiling point of water, which is 212 degrees Fahrenheit at normal atmospheric pressure.

Those of you who are using thermostats that are set to an extremely low temperature may have just recently come to the realization that your engine that is operating at a colder temperature may not be as well protected against wear from the inside of the crankcase if you are not removing the water vapor.

This is one of the reasons why I typically maintain the temperature of the thermostat that was originally installed in the majority of my performance street vehicles. In addition to the temperature setting of the thermostat, short journeys that do not enable the engine to warm up completely also contribute to the formation of sludge in the crankcase.

Therefore, it is a good idea to drive the vehicle for a sufficient amount of time to cook off the majority of this material and then allow the PCV system to pull it via the combustion process as vapors.

Next, what is the best way to expel the vapors? The process is not overly complicated when using a naturally aspirated engine. At this point, all that is required is to connect a hose from the engine valley or valve cover to the intake manifold.

Vapors are drawn into the intake manifold by the engine’s vacuum, where they are combined with the rest of the new air and fuel as they travel through the combustion chamber.

The majority of the harmful substances are converted into carbon dioxide and water when they exit the vehicle through the exhaust after being burnt in the combustion chamber and traveling through the catalytic converter.

In order to prevent the crankcase from being over-scavenged, which might potentially cause engine seals to be sucked inward, the PCV valve serves as both a check valve and a flow-limiting mechanism.

Its purpose is to ensure that things only flow in one direction and with the appropriate intensity. Because the suction is at its highest when the throttle is only partially open, we experience this phenomenon more frequently when the throttle is only partially open. In most cases, a second vent line is connected to the air input hose that is located behind the air filter.

This allows for clean, fresh air to gently replace the harmful substances that are being removed by the PCV system.

In the event that we have a significant amount of blow-by when under high load, the flow may change direction, and the line that leads to the intake tube may also assist in releasing the surplus gases into the throttle inlet.

In an ideal environment, there would always be a tiny pressure depression between the crankcase and the atmosphere outside the engine. The exterior seals and piston rings are maintained in the correct position as a result of this.

Keeping this in mind, you might be curious about the consequences that might result from installing a turbocharger or a supercharger on our engines. Because of the high pressure that is present in the intake manifold and the pipe that leads into the throttle body, we will require a separate route for the gasses that are produced by the crankcase to escape.

There is a possibility that we may have a variety of problems with the PCV system if we do not carry out cautious planning. We may learn how to manage the problem in the most effective manner by looking at how OEM turbocharged applications are handled.

The very first item that we want is a dependable check valve that will be installed between the crankcase vent lines and the intake manifold.

Having our strong compressor operate against the intake manifold while also pressurizing the crankcase is something that we do not want to happen. If the factory PCV is not strong enough to withstand boost pressure, the majority of boosting kits will add a dedicated check valve.

However, this only prevents us from adding to the existing crankcase pressure with the supercharger, and it also cuts off one of the main escape routes for the crankcase gases just when we need it the most. This is because cylinder pressures (and blowby to the crankcase) rise in direct proportion to torque.

As a result of the fact that torque is directly proportional to the working pressure within the cylinders, it follows that the greater the torque that we generate, the greater the amount of combustion gasses that escape through the rings and into the crankcase.

The blowby gasses have the potential to cause a significant amount of pressure to be built up inside the bottom of our engine if we continue to do this for a period of time that is longer than a few seconds. The consequences may include an increase in windage as well as sufficient pressure to force out the seals on the crank and valve cover.

The additional pressure that is placed on the bottom of the pistons can also result in ring flutter, a significant increase in bore wear, and even greater cylinder leakage. In a performance engine, lowering the pressure in the crankcase when the engine is under load ought to be a top focus.

The utilization of many stages of scavenging on dry sump systems is another explanation for why high-performance racing engines are designed in this manner. Its use extends beyond just collecting the liquid oil.

Additionally, this pressure is applied in both directions across the piston rings. It is possible for there to be a condition in which gasses and oil can sneak into the cylinders during the intake stroke if there is sufficient pressure in the crankcase.

This occurs when the intake stroke is producing a strong vacuum. Not only are we wasting important space in the cylinder, which might otherwise be used to generate more power by allowing more fresh air and fuel to be charged, but the oil that is being sucked in also significantly increases the likelihood of knocking. This is a double-edged sword.

Because oil has an octane value of 48 or below, it is sufficient to use only a little amount of oil in order to reduce the consumption of the intake charge.

In order to assist in the process of separating the liquid oil from the vented gases prior to reintroducing them to the inlet stream, original equipment manufacturer (OEM) systems frequently incorporate screens, tortuous pathways, or even cyclonic separators.

When there is positive manifold pressure, the PCV system of a boosted engine need to have a clean channel for ventilation to pass through. Utilizing environment as a means of escape is a lazy way out.

In addition to being a blatant violation of emissions regulations, it is simply not as effective as scavenging in the correct manner using suction. Oh, and nobody loves having a breather that is pouring with oil and is a mess as it drips all over their engine compartment. Not only is that a mess, but it also poses a risk of fire.

If we want to actively suck the pressure out of the crankcase when it is under boost, we should instead find a mechanism to apply suction to the crankcase at either the valley or valve covers (the more access we have to various spots in the crankcase, the better).

To do this, the ventilation lines must be redirected to a source of suction, such as the compressor inlet, rather than just being sent toward the atmosphere. This is accomplished by original equipment manufacturers (OEMs) by connecting the air filter to the compressor inlet, which is located in an area where there is a natural depression during high load that can assist in actively drawing vapors from the crankcase.

In addition, contemporary engines feature excellent bay-to-bay breathing that extends down the length of the block and good pressure equalization that is applied to the valvetrain.

As long as there is always a low-pressure escape line, this indicates that vapors may be pulled from only one or two spots and yet successfully regulate pressure throughout the whole bottom end of the engine to slightly below atmospheric levels. This ability is only possible if there is a low-pressure escape path.

It is time to return to the second function of the PCV system, which is the separation of liquids. Modern factory valve and valley covers have intricate passageways that make it difficult for liquid oil to travel through.

This is due to the fact that the heavier liquid tends to adhere to the walls of the built-in separator, which makes it harder for the liquid oil to pass through. Because of this, presumably the majority of the liquid oil that was suspended in the vapors will be removed.

On the other hand, we could want a little bit more assistance in this regard with high-performance engines that have a higher cylinder pressure and blowby. At this point, catch cans or external separators can be of great assistance in preventing oil contamination of the incoming fresh air charge when the load is considerable.

The actual separation of liquid and gas that takes place within the apparatus is accomplished using either a winding path or a cyclonic movement system.

The most effective versions of these will be built in such a way that the usual airflow through the PCV is maintained, so avoiding the release of pollutants under any circumstances other than the most severe ones. Irrespective of the emissions, we still do not want to blast greasy vapors through a filter in the engine compartment since it would create a mess and there is a risk of fire.

If the design of the separator is excessively restrictive, it is important to keep in mind that it is possible for the separator to impede the flow of the gases that are exiting when the load is high.

On the other hand, even if they are performing an excellent job of preventing oil from entering the intake, it is possible that they are compromising their efficiency in the primary duty of venting the gasses. When it comes to this particular aspect, cyclonic separators perform significantly better than basic catch cans or convoluted-path strainers.

This is because they maintain the gases’ swift motion. Having a setup that is correctly sized is absolutely necessary in order to prevent any substantial restrictions from occurring within the range of vapor flow that you have forecasted. For most V-8 engines, it is recommended to begin with a line that is no less than 3/8 inches (-6 AN).

However, for more aggressive installations, it is recommended to use a line that is either ½ inch or 5/8 inch (-8 AN or -10 AN) to and from the separator.

Due to the fact that there is a specific amount of pressure drop per foot caused by the internal drag, the length of this line is directly proportional to the importance of size. Always go up a size when you are unsure.

It is possible for certain separators to be completely maintenance-free by reintroducing the liquids that have been collected back into the oil sump and allowing the oil filter to handle the cleanup in the typical manner.

The finest turbocharged original equipment manufacturer (OEM) systems of today operate in this manner, which eliminates the nasty task of manually draining the can.

In the event that you connect a drain line from your separator to the oil sump, it is imperative that you incorporate a check valve. This will ensure that the PCV suction does not pull oil up the pipe that is being vacuumed.

When the engine is drawing oil into the chamber, it is extremely challenging for a tuner to eliminate knock. This is because the work gets more complex.

It makes no difference whether this was brought in simultaneously with the airflow or if it was drawn in after the rings on the intake stroke; the outcome is the same either way.

It is possible to lessen the knock by including enough airflow and isolation, which often results in increased horsepower. The engine will also have a longer lifespan as a result of this, as the oil will remain in better condition while it is being used.

All you need to do is make sure that the PCV vents are not blocked off or left exposed to the atmosphere, and you should get significantly improved results.

How to Build a Functional PCV System in Performance Engines – careerscholars.com