Every car has a positive crankcase ventilation system. The PCV system is designed to regulate and remove fumes out of the engine crankcase, and to alleviate pressure which could cause oil leaks or seal damage. All in all, it’s a way for gases to escape in a controlled manner from the crankcase. Think about how high your cylinder pressures get and how much gases the combustion creates. Your piston rings create a seal to push as much of it as it can out the exhaust valves during your exhaust stroke. There is still a small amount of unburned ignition mixture that leaks past the piston rings and down into the crankcase. This leaking mixture is called blow-by.
The blow-by pressurizes the crankcase and needs a way to escape. When your PCV valve opens, the engine’s vacuum essentially sucks out the pressure. Coming out with the pressure is the blow-by gases and oil mist. It’s a mixture of unburned fuel, oil, and other contaminates that are diluting and creating a scary cocktail of your oil. When oil is mixed with the intake charge, it significantly reduces the knock threshold of the fuel. Let’s say I spent $15 a gallon for some 110 race fuel, but I have my PCV pumping oil through my intake. Oil burns really easily, so it destroyed the knock threshold of the nice high octane fuel I bought.
For this reason, oil catch cans were created. The catch can is added into the PCV system before the intake. Inside the can should be a series of baffles that the mixtures would cling to, solidify, and drip to the bottom of the can. Then after the mixture has passed through the can, it is routed back into the intake (hopefully as free of contaminates as possible).
A lot of the catch cans you can buy are just an empty can that doesn’t actually catch anything. Make sure you are buying a can that will function properly or else you are essentially throwing money away. It’s worth it to spend extra so that you don’t blow up your car. Looking at the pictures below, you can see the baffles that oil solidifies on. I highly recommend getting one of Mishimoto’s two filtered cans, not only are they baffled but there design also have a brass filter in them as well. They offer both a small compact design and a big capacity design. This filtered designs offer even more piece of mind so you can boost happily, hopefully, for a long time.