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Catch can installation and explanation

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PCV Catch Can

CLICK HERE for my new catch can design and install

What is it?
A catch can like the name implies is a can that is set somewhere in the PCV line to catch any moisture or oil spray that may exit the engine block.

How does it work?
Basically, as the engine is running, blow by from the cylinders builds up in the crank case. This positive pressure has to escape somewhere, hence PCV (Positive Crankcase Ventilation). Along with the escaping gases some oil mist and moisture also leave the crankcase. In the old days this use to be simply vented straight out into the atmosphere however the evolution of the EPA and emissions controls soon put a stop to that. In order to keep these escaping fumes from entering the atmosphere the positive pressure was simply diverted back into the intake and was burned by the engine. The problem with simply directly connecting the PCV to the intake though is that all that oil mist and moisture would also go into the intake are gum up the engine rather quickly. The catch can was born.

Different types of catch cans.
Most every car engine has a catch can from the factory. This can usually sets somewhere on the back of the block and on Hondas it is what the PCV valve hooks into. The OEM can is very primitive, and usually collects the oil and moisture and then lets it run right back into the crankcase. This not only degrades the oil but also, over time, allows moisture to build up in the crankcase. The solution to this is to separate the catch can from the crankcase. In this setup though, the can will need to be periodically emptied of its collected contents. Some catch cans have an input and output. The input is where the fumes enter the can, the oil and moisture is separated out, and then the output would be run back into the intake as the OEM setup did. Most of the time though, if you are running an external can, you will want to simply vent these fumes into the atmosphere as they can lower the octane of your burning fuel quite a bit. For this some cans simply have a small breather instead of an output.

There are a few different ways to install a functioning catch can. The simplest way is to remove the PCV valve and install a straight through hose coupling in the valve bung. To this you would attach a hose and run it to the catch can, usually attached to the firewall somewhere below the level of the cylinder head. In newer cars you will have 2 openings in the block, one for the PCV valve and also a vent usually in the valve cover. Some catch cans have 2 inputs just for this purpose. DO NOT hook both vents up to a can that is not designed for it. If your can only has two hose hookups such as the one I installed, and you hook both crankcase vents to it, there would be no place for the escaping fumes to go, they would simply pressurize the can and the crankcase and possibly damage the engine. Remember, the gases that enter the can have to leave somewhere. In my setup I ran from the OEM PCV valve bung into the can and then vented that under the car. The top valve cover vent simply vents under the car as well with no can, since it is from the valve cover not much moisture or oil mist exits. For now I left the OEM can in place but plan to remove it in the future to keep any moisture from reentering the crankcase.