“Catch Cans” & Why They’re Necessary…

While many high performance car enthusiasts are familiar with catch cans and their importance, many customers we talk to have not heard of them.

Likely every car owner, however, has heard of the term “PCV valve” from a service advisor at an auto dealership.  While the Positive Crankcase Ventilation (PCV) valve has some interesting origins stemming from World War II tanks, its use in modern cars is primarily for pollution control purposes.

During normal engine operation, some combustion gasses make it past the pistons and rings into the crankcase as opposed to out the exhaust manifold.  This buildup of gasses in the crankcase creates pressure.  That crankcase pressure is a bad thing—makes seals leak and robs engine of performance and efficiency.  To address the crankcase pressure problem, Crankcase Ventilation (CCV) systems were used to relieve the pressure.  Before the early sixties, CCV systems relieved crankcase gasses pressure with open tubes and breathers that vented to the atmosphere.  Well, the EPA decided this was a big pollution contributor, so the PCV valve was introduced as part of the CCV system.  The PCV valve is a one-way valve that allows gasses to exit, but not enter back into, the crankcase.  On the exit side of the PCV valve, a hose is routed to the intake manifold so that the only way crankcase gasses can exit is eventually through the exhaust, where the catalytic converters make the gasses more acceptable to be released into the atmosphere.

The problem with routing crankcase gasses back into the intake air stream is that those gasses also carry with them a mixture of oil, unburnt fuel, sulfuric acid and water vapor, among other things.  This dirty mixture has several bad effects for engine performance.  It effectively reduces the octane of the fuel, fouls plugs thereby reducing their life and ignition effectiveness, and generally reduces engine efficiency and power.

A well-designed catch can or “oil-air separator” system that effectively “scrubs” the CCV gasses before they are reintroduced into the intake air stream can largely eliminate this problem.  One system we like to use and recommend is made by RX Performance.  Most products out there involve using a single “catch can” that uses a metal can with some sort of filtering that is plumbed into the car between the PCV valve and intake manifold.  RX Performance, however, uses a 2-sided approach.

ProCharged C7 with RX Performance catch can & oil-air separator installed by FRANJO SPEED

ProCharged C7 with RX Performance catch can & oil-air separator installed by FRANJO SPEED

On the “dirty” side—the side of the motor with the PCV valve—RX Performance uses a large catch with single or dual valves, depending on application.  On the bottom of the RX Performance catch cans is a valve that you periodically open to drain the oil/gas/acid/water crud that is being kept out of your intake air stream.  The advantage of the RX Performance catch cans versus others is that they trap all—or nearly all—of the oil and other contaminants from the crankcase gasses.  Most other catch cans on the market remove only 15-30% of the suspended compounds, allowing the remaining 70 – 85% to pass through and be ingested.  To be really effective, all or nearly all of the vapor contaminants need to be removed.  For forced induction applications—where blow by gasses are an even bigger problem—RX Performance offers a “Monster” (i.e., really big) 2-valve catch can.  RX Performance’s Monster system is one of the only complete solutions for turbo charged and centrifugal super charged applications that provides proper contaminant evacuation during both boost and non-boost operation.

Then on the “clean” side of the motor where there is typically a CCV hose running from the oil fill tube in the valve cover over to the air box just behind the air filter, RX Performance uses a “Cleanside Separator”.  The Cleanside Separator keeps oil in the valve cover and lets only clean gasses back into the intake stream. Most other catch cans on the market don’t address the “clean” side at all, even though contaminant carrying gasses can still make it into the intake from this path (especially on forced induction applications).

Mustang GT500 catch can & oil-air separator installed by FRANJO SPEED

Mustang GT500 catch can & oil-air separator installed by FRANJO SPEED

To maintain power, efficiency and the life of your plugs and other components, every performance car should have a proper catch can and oil-air separator system.  For forced induction cars, it is a must.  At FRANJO SPEED, we have installed many of these systems on a variety of cars.  Give us a shout to discuss your particular application.

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2 Responses to “Catch Cans” & Why They’re Necessary…

  1. Bob jones says:

    i have a T-Bucket with a Chevy 350 small block.it has the oil fill tube and breather in the front of the motor.i have tryed all types of breathers but get oil drops on the fire wall and right side of car!!!!!! can you help? thank you!

  2. Frank Bick says:

    Hello, Bob. Thanks for contacting FRANJO SPEED. If you can drop by with the T sometime over the next couple weeks, we’d be happy to take a look at it an let you know what we think.

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