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Automobiles are set up and sold this way from the factory for EGR/emissions purposes. This process continually recirculates built-up pressure, along with a fine oil mist back into your intake, and onto the top of your valves. The downside with this approach is that it can create gunk and sludge buildup which over time restricts the available air-flow your engine will receive.
A catch can’s job is to stop the oil that is thrown into the PCV valve along with that pressure from reaching the intake. It will keep your intake manifold cleaner than running without one, prevents buildup of contaminants and air restricting carbon, allows you to conserve more oil for longer, maintains emissions health for the environment and even reduces harmful exhaust fumes accompanied by burning oil.
To install a catch can, the inlet hose is routed from your existing PCV valve on top of your valve cover into the inlet port on the catch can. This inlet hose is typically designed to sit lower than a baffle or a filtration component. This allows incoming air and oil into the can, but only air is allowed past the filtration element upwards. The outlet hose is routed from the outlet port on the catch can back into the intake port for your existing PCV. This is designed to let clean, uncontaminated air back into your intake system while collecting and keeping the oil which would have been burned in the intake process.
These filters are replaceable and should be checked, if not replaced at least once every year in an actively used vehicle. One plug, or even a hose with a petcock can help to drain and clean out any oil the catch can will have collected.
As with pretty much any auto part, not all catch cans are made equal and some differ greatly in design and functionality from others. For example, certain iterations like the ones made by Nuke Performance have a dipstick built in to assist with checking the level of oil inside:
This makes it easy to tell when they need to be drained. A good catch can will also have a proper baffle on the outlet side to further prevent oil from getting sucked back up, as mentioned above:
Some cheaper versions may use an open vent to release air out of the top of the can into the atmosphere. These designs are not only ineffective, but also harmful to the air quality around us and contribute to smog. Releasing emissions and unburnt engine fumes also defeats the purpose of the PCV and renders the re-usable pressure and circulating air useless.
We encourage you to do your research on catch can before buying. Generally speaking, whether a catch can has a dual inlet, single filtration construction or a baffled single inlet and outlet, the purpose stays the same. We’ve seen many cans on the market that don’t even have that, which is why we carry the Nuke Performance units. Their catch cans include all the features required for a high performance or race car.