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Here are some Hints and Tips on how to plumb and connect our PCV valved breathers and breather tanks for maximum performance and efficiency. PCV systems prolong oil life, reduce oil contamination and promote engine sealing when there is vacuum, and an open breather system is a last resort or when running wide open throttle for most of the engine's operating cycle.


Many think that PCV valves are "evil emissions equipment", and do not belong on an engine, let alone a performance mill. This couldn't be farther from fact. A good working PCV system is MANDATORY for any engine that is intended to produce optimum performance while providing maximum durability and longevity.

The PCV (Positive Crankcase Ventilation) valve's primary function is to allow the induction system to suck fresh air via an inlet (breather) through the crankcase of the engine, and into the combustion chamber. The vacuum created by the engine's normal pumping process produces the necessary suction to pull air from the crankcase. Since a one-ended suction alone wouldn't allow any air to be moved at all, an inlet vent, or "breather," is needed to allow fresh air to enter, thus promoting a constant airflow through the crankcase. The PCV valve itself is metered as to not create a significant "vacuum leak," thereby interfering with the normal operation of the engine. A PCV pull's it's valve open which vacuums out the engine under all conditions other than a low vacuum situation, for instance, when the engine is under a heavy load. For engines that spend more of their time under full throttle than not, they would be better served by a "scavenging PCV system," which usually gets it's "vacuum" by siphoning air flow off of the headers.

The benefit of a full working PCV system starts off with creating a positive vacuum in the crankcase, thereby reducing potential oil leaks past gaskets and seals, as well as pulling the oil rings tighter on the bottom sides of the piston, which in turn result in better cylinder efficiency, less blow-by, more power and less fuel used. The primary benefit is, the constant airflow "vacuums" all the harmful contaminants, acids, moisture and airborne dirt from the engine's crankcase, thereby increasing engine life, oil life, and overall performance.

This particular PCV valve is a disguised billet aluminum valve cover cap (yellow), with the PCV valve itself hidden inside, (aesthetic purposes only). The seal on the grommets need to be tight, and there needs to be an unrestricted passage under the grommet that might interfere with valve cover baffles, etc. Baffles in the PCV and valve cover will reduce the possibility of the suction picking up oil mist, drawing it into the combustion chamber which may result in unnecessary oil burning at the exhaust.

The inlet to the intake
(red) must be centrally located. If the PCV flow is drawn from a single intake runner, the vacuum drop in that one port and cylinder might result in a too-lean condition, possibly burning a piston or valve in that cylinder. The optimum location for the PCV inlet is under the plenum of the intake. A hole drilled and tapped can be done by taking off the carb, lining the intake with oiled paper towels to catch the chips, then removed to eliminate any debris from entering a completed engine in the car. Care must be taken to insure the PCV valve is always fully operational, and not gummed up. Shaking or sucking through the PCV occasionally will insure this.

The breather inlet (yellow) is also a matching billet cover matching the PCV cap. And important feature of any inlet breather is that it be shielded from forward airflow (fan, etc), where the wind blowing past an open style breather would try to "siphon" oil up and out of the valve cover and onto the exterior of the engine and headers, potentially causing a fire, besides the never ending greasy mess.

Since the air supply is vented in from the breather, there needs to be a filter inside, otherwise you'll be drawing in unfiltered air through the belly of you engine. The breather inlet should be on the opposite valve cover, as far away from the PCV valve as possible. This will sweep the entire engine clean of internal gaseous contaminants.

These contaminants get there from the inherent blow-by past the rings, however slight, as well as unburned gasoline passing past the rings during cold start up into the engine oilů especially with larger cammed engines, and those taking short trips. Moisture from condensation also gets into the engine, which needs to be vacuumed out with fresh, clean air. Thus, the PCV to the rescue!

HINT: The PCV (Positive Crankcase Ventilation) valve needs to be the correct size for your particular engine. The PCV's job is to 'vacuum' the crankcase free of oil contaminants and to promote further ring sealing because of the vacuum. If the vacuum volume is too high, such as in a large cubic inch engine, then the PCV valve needs to be more restricted. A smaller 4 cylinder engine would require a higher flowing valve. This is why it is important to get a valve which was designed for your particular vehicle! Also be sure to check the SEAL of the valve, and not simply rattle it to determine the operation of the PCV valve.

Sharing the Brake Booster Vacuum w/ PCV System

DETAILS: You may have heard that sharing a common inlet to connect both the PCV valve and the brake booster vacuum reservoir together in not advisable, yet you also may hear of others who say it works just fine. While it may work, it should be avoided if at all possible.

The reason this can even work at all, is that the vacuum reservoir for the brake booster fills up when it gets the chance from any extra vacuum the PCV is not bleeding off. This only happens once in a while and for a relatively short period of time under heavy deceleration, thus the interference to other devices sharing the same vacuum feed can be minimal... or not.

However in multiple pump braking situations it takes more time for the brake booster to be recharged and reach it's peak capacity, therefore the power assist for the power brakes will be diminished until the maximum vacuum level can be re-achieved. This would be the primary concern regarding sharing the brake booster source with the PCV, especially when utilizing large overlap camshafts that have even less vacuum at idle than less radical cam profiles. In some of these engine applications the PCV will drain off any extra vacuum the engine may generate leaving little or nothing to the brake booster reservoir.

It is advisable to keep the PCV vacuum source port separate from anything else for the above reasons, not to mention the possible contamination of the brake booster with oil contaminants from the PCV and/or fuel from the intake manifold. As an example, you have oil vapors running from the valve cover to the intake manifold under normal PCV operation. If the brake booster needs a charge of vacuum and the conditions are right, there is nothing stopping the flow of oil vapor normally going to the carb from re routing right into the brake booster. Furthermore, if the carb backfires, while the PCV valve is designed to close, the air/fuel mixture could be delivered to the neutralized brake booster during the split second it takes for the booster's one way valve to close contaminating it with fuel as well. If you wish to test and diagnose this condition simply remove the vacuum hose at the brake booster and notice an oily film that has accumulated on the hose end, or a the pungent odor of fuel when the hose is removed.

SOLUTION:  So, what then would be the "best" street solution to getting the best of both worlds? The PCV would draw from a separate location off of the intake manifold while the brake booster draws from a separate port. While the brake booster can draw from a single intake runner (since it's vacuum source is only momentarily bled off after the brake is released and usally not while under power), but since the PCV creates a constant controlled "vacuum leak" during it's operation, it could otherwise lean out one cylinder if ported off of a single intake runner or in a divided dual place plenum. This could result in severe engine damage by leaning that one cylinder out, and therefore the PCV vacuum source must come from a common source all the cylinders can draw from, like an open plenum from under the carb or a carb spacer with a larger 3/8" PCV port in it.

While a single open breather on one valve cover and a PCV valve on the opposite cover is acceptable, the best scenario would be an open inlet breather on each valve cover and the PCV valve located in the center of the intake manifold base (baffled to filter oil splash from the lifter valley) taking in crankcase ventilation from the valve lifter galley area which is the center of the engine. You will have double the breathers under WOT and still maintain a fully operational PCV system.

Sharing the Brake Booster Vacuum w/ PCV System