50 replies to this topic

[TerrA LX]

Nothing wrong with a good catch can system.

[Litre8]

What's the intended use? For normal driving the factory fitted PCV system handles these duties ok.

[TerrA LX]

Burning oil is not a good thing.

[TerrA LX]

^^ IMO better than just plumbing the PCV straight into the manifold but I prefer to have a sealed system with a PCV and a catch can for registered street cars.

FWIW any car will benifit in more than one way if you can stop oil entering the combustion process.

[Litre8]

With a proper dry sump setup on a fresh engine you can effectively seal the engine....no breathers required, the scavenge effect of the pump should pull a vacuum in the crankcase..

[TerrA LX]

So there are breather types and ones i have seen without breathers , the sealed types still have to vent somewhere though dont they?

What I mean is run the factory set up with a sealed (non vented) catch can after the pcv, before the manifold, so you still retain the benifit of the PCV operation.
This alone does not address the high speed operation as this system vents to the air cleaner.

[ls2lxhatch]

Yeah thats what i was thinking , what about running 2 breathers like the one i have on my drivers side rocker, put one on the passenger side?

On a V8 the factory system sucks filtered air through the hose connected to the air cleaner, into one rocker cover, through the crankcase to the PCV valve on the other rocker cover and then into the intake manifold. This is called positive crankcase ventilation as clean air is forced through the engine to remove vapours.

Positive crankcase ventilation is vital to maintaining oil quality. A system that has only breathers connected to the rocker covers without a vacuum source will result in contaminated oil.

You need to either use the vacuum from the intake system or you can use the vacuum generated by the exhaust in a vehicle that is not used on the road. When connecting to the intake system make sure that all cylinders are fed by the connection, do not connect to a single intake runner.

This is a good article on the subject.

This is the catchcan system and filter I am considering for my street driven LS2. The filter will guarantee that oil will not enter the intake system which I think is important for fuel injected engines.

On a carburetter engine any oil bypass from the PCV into the intake system will be cleaned by the air/fuel mixture. However port injected engines have nothing but fresh air running through the intake system which will eventually become coated in oil that has bypassed the factory PCV system. It is also worth noting that K&N style filters can also lead to oil buildup in the intake systems of port injected engines.

Edited by ls2lxhatch, 18 June 2009 - 01:55 PM.

[TerrA LX]

On a V8 the factory system sucks filtered air through the hose connected to the air cleaner, into one rocker cover, through the crankcase to the PCV valve on the other rocker cover and then into the intake manifold. This is called positive crankcase ventilation as clean air is forced through the engine to remove vapours.

Not at all RPM/Throttle positions, this is why it is called a PCValve, when it closes the engine still vents to the air cleaner.
Some guys run a single open filter or breather on this side as SS Hatchback has stated.

[ls2lxhatch]

The purpose of the PCV valve is to regulate the airflow through the engine. When vacuum is high the valve reduces airflow, when vacuum is low the valve is fully open allowing maximum airflow. Even under extreme vacuum the PCV valve should not completely close.

The primary purpose of the vacuum is to draw clean air through the crankcase to purge crankcase vapours and reduce oil contamination. In a vacuum system changing from a breather connected to the air filter to a single breather on the rocker cover will have little effect as air should be entering via the breather not venting.

Fitting a second filter to the other rocker cover as SS Hatchback suggested in a vacuum system will short circuit the system. The majority of airflow will be through one rocker cover which will reduce the efficiency of vapour scavenging and increase oil contamination.

Fitting a filter to both rocker covers in a system that does not incorporate a vacuum would be an improvement over the single filter.

Many of the catch can systems on race cars are purely designed to relieve crankcase pressure. In those setups crankcase pressure is vented via the filter on the catch can. A vacuum is not used to purge crankcase vapours and as a result the oil will become contaminated. Oil contamination is not a primary concern in a race engine but it should be a primary concern in a street engine. If you fit this type of system to a street car and only change the oil every six months you are asking for trouble.

[dattoman]

Most of us aren't dry sumpers

I would assume on an engine with Forgies you'd want a system as you have higher clearances when cold

Most drag cars run breathers as they run a fair amount of blowby on the rings.... you'd be suprised how much actually

[Tiny]

And Shiney is GOOD

I run a catch can and it does it's job...

I didnt want to run a PCV setup cause i didnt want that crap going hrough my carby and being re-burnt.

However it's illegal in in NSW as well to have it ventilated to atmosphere, You must re-breathe the vapors.

A vac-u-pan setup is another way of using the exhaust gas speed to pull a vaccum on the engine and get rid of the gasses - again not legal in NSW.

I'm going to keep going with mine for now!

[Heath]

Better for the environment with a sealed catch can anyway. It's the way to go as far as I'm concerned.

[TerrA LX]

I was told by an engine builder that you'll blow out your rear main seal if you give your motor a hard time with it hooked up.

Thats pretty much why the factory system vents into the air cleaner, when the revs go up and the manifold vacuum goes down the PCV valve closes off, the pressure from the crank case has to go somewhere.