Here is a post we made on the differences between tanks that pretty much covers some of the details on a oil catch can.
Oil catch can, air oil separator, breather reservoir, catch tank?
Hello automotive gurus. Often the term oil catch can is used and it covers all tanks used to catch oil. More specifically there are two types of tanks that catch oil from the crankcase/vapor.
The oil catch can with a breather or “filter” on top is a “breather” with a reservoir or tank to accumulate or catch oil. The vapor escapes into the atmosphere so its a open air system. These are used without engine vacuum. The baffle inside a breather tank does not have to be complex. The baffle only helps prevent oil from exiting or getting on the breather/filter. On rally cars, trucks doing jumps/dune buggy, UTV or extreme drag racing its best to have more baffle to prevent splashing up onto the inlet but most applications work great with a simple baffle. With large engine block or valve cover outlets in the 10mm or 1/2inch range you can help prevent crankcase pressure from ever increasing. When doing so you will not only catch some oil from the vapor but also from the rockers, cams and springs throwing oil around. Its also important to note you can catch more oil with smaller outlets as the velocity is higher. Imagine a 3inch tube connected to your vacuum, its going to be hard to suck up dirt since the focus of velocity covers a large area. The other important issue is pre catch can baffling… outlets on the valve cover or block can be a culprit… baffle these so splashing oil can not easily be tossed into the fitting and thus the oil catch can. This internal baffling will help reduce your caught oil.
Another related factor is using a breather tank with a vacuum pump. For higher horsepower applications or when performance is key and cost does not matter is the addition of a vacuum pump. Thus the engine connects to the pump and the pump flows into a breather tank still. Its best to have a dual breather tank that has increased tank outlet flow for the additional fast high flow velocity that a single -12an outlet pump will flow. These pumps will require a complex or custom bracket, and so a belt and pulley off the crank or alternator will be needed.
Air Oil Separator:
The Air Oil Separator is a much more complex baffled tank that is closed off from the atmosphere. This closed system is much like stock and the engine vacuum helps draw the vapor out of the crankcase and put a vacuum pull on the piston rings. The downside to these tanks: 1. They cost more as the engineering is more complex. 2: It sends burnt oxygen lacking air back into the engine. and 3: Oil can still get into the intake.
The elements or baffles inside can be quite complex and much like a shop air compressor oil/air separator removing all the oil fragments from the air flow can be challenging while still allowing amazing flow through.
Alternately you could use exhaust venturi effects or a electric air pump to create suction but balancing the suction rate based on rpm and thus engine crankcase output can be challenging. Getting the right rate close to creating 12hg of vac (what I have read) on the rings helps them seat and more power can be made by helping the seal and preventing additional crankcase pressure.