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July 13, 2020 3 min read

Why You Need an Oil Catch Can on your Turbo or Boosted Engine

High horsepower and more notably BOOSTED engines create conditions in an engine that are not typically or ever seen in their factory form.  Pressure built by faster moving engine parts, wider ring gaps, looser tolerances, and stresses on components can allow for crank case pressure to increase.  Not allowing the excess crank case pressure out can cause even more issues including: seal failure, loss of horsepower, oiling issues, and even fire hazards as oil exits seals.  There are two types of catch cans that exist, but only one truly is appropriate for high horsepower applications.

Style 1: Closed System Cans

Factory vehicles are often equipped with a closed system particulate catch can.  This is nothing more than a can that oily pressurized air passes through in an attempt to knock the oil out of the air.  With the hopes of it collecting at the bottom of a container, some drain back into the oil pan, some do not.  The air coming out the otherside of the can then enters back into the intake after passing a PCV check valve.  These valves insure that air enters in a one way fashion.  This style system can be a vacuum leak if simply disconnected and not capped off, and can change how your tune acts. Additionally, because the air is brought back into the engine, it will contain a certain amount of particulate.  This is why factory intakes usually are oily and sludgey on the inside.  However, that cleanliness is not the only drawback.  Oil being present in a fuel charge can cause detonation and tune issues.  On a Nitrous or Boosted engine it is even more detrimental.  


Style 2: Open System (Vented) Catch Cans

For a modified and high horsepower application, this is really the only logical choice.  A vented catch can will 100% eliminate an oily air charge from getting into your intake (Most Important).  An Open system will also be more effective at removing the crank case pressure as a whole. 

An Open system simply caps off the intake port where the air would recirculate into the intake (most MAF sensor vehicles will need a tune update for this to be possible).  To hook up the catch can, the user would then take a line off of each valve cover (sizing varies depending on application), and connect each line to an inlet on the catch can.  For large High Horsepower Boosted and/or Alcohol vehicles (usually 1400+ HP) we will recommend two large cans to be safe.  

The lines from the valve covers act as an escape route for built up crank case pressure. From there, the air will enter the catch can and go through a series of turns and baffles.  This will knock the oil particulate out of the charge before it turns the corner and heads out of a small air filter at the top of the catch can.  

Where Open Systems get a bad rap from is in early days and designs.  Early catch cans were simply fittings welded to a can with a filter on top.  This would allow the oil filled air to travel directly into the filter, causing an oil soaked filter.  In the old days you would see people wrap socks, rags, sweat bands on the filter to keep it from dripping oil everywhere.  

Another tip is to baffle the fittings on your valve covers.  That is your first and best line of defense.  The air is positive pressure, it will find the low pressure escape route.  Adding baffling allows for proper ventilation, but keeps the oil in the engine.  Thats what we want afterall.

It is important to note this is not a vacuum leak, crank case pressure is completely separate of the pumping side of the engine where your intake and cylinders are connected to.  If this is a vacuum leak, your engine has some real issues!  

Conclusion

While some closed catch can systems will do a better job than others getting oil out of the air, it comes at a cost.  PCV and check valve failures can get ugly in a hurry, in fact those can be a whole headache and dangerous system in their own.  The pressure will potentially eventually build up and burst a line or cause oil to spray everywhere or worse. We have even heard of engine bay fires as a result.  

Some closed catch can systems will fill the catch can full of steel wool or another mesh to keep oil out of the outgoing line that is headed back to the intake.  Of course that comes at a cost and price reducing can volume as well as the potential of gumming up and clogging causing lower flow rate.  

For a complete list of our catch can products click the link below!

https://www.motionraceworks.com/collections/catch-can-pcv


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