ok got problem , how are the blown boys controlling the pcv / crankcase venting on the blown engines ,when replying include whether you draw through or blow through

You have two sides to the breather system on most cars.

You have the PVC side which only operates at idle and cruise. It is very important to retain this for emissions, I personally think it helps with economy (wont go into this) and essentially can remain as the factory set it up. Wont affect performance
Some have experienced the plastic pcv valve break with turbos but this can be replaced with a metal one. You can also put an additional one way valve inline to make sure it does not leak under boost.

Then you have the breather that leads from the other end of the rocker cover to the throttle body.

This does two things. It allows some air to come into the engine when the PCV is under vacum. Under load it allows blowby to escape and that gets burnt up in the engine.

When turboing you need to disconect this from the T/B and plumb it into the turbo air intake. Can also put to catch can.
However the tiny hole for stock applications is not big enough for performance modifications and needs to be made bigger to vent off more.


There are many ways to skin a cat but this is the setup I am currently doing. I am doing two catch cans. One catchcan is for the PCV side. It catches the oil during cruise and idle and sends it back to the sump.

For the other side I am using about a 30mm hose conection that leads to a catchcan (which drains into the sump) which then leads to the air intake.

I am not venting to atmosphere as I intend getting this car emissions passed.

To answer your question it is drawthru on cruise/idle and blowthru on load.


Just venting both points to a catchcan is not the right way.

i've thought bout draining catch cans back into the sump but a: if it's not valved then what stops it sucking back all the oil from the sump?
and b: the condensation mixed with the oil creating awsome creamy sludge that comes out of the drain in my catch can from time to time kinda turns me off that idea

Yes you do have to work out the one way valving and finding one that allows the oil to flow during engine shutdown and close when they have to.

Re sludge: Important issue. I think this would be an issue only on the PCV side as this operates continuously on cruise and idle. If you have a basic breather setup there should be no alteration to the PCV side in the first place. I am only doing a catchcan on the PCV side as an experiement on keeping the engine/intake manifold cleaner/better economy and accept this issue but most people doing a basic breather setup should not be touching this side. I think using synthetic oil helps a bit with regards to this aspect (I have read)

I have never had this issue on the venting side as this only operates when the engine is under load.

this is correct but do you want to be venting sluge into your sump ? a catch can on the breather side is a complete waste of time imho. how much oil do you recover from the breather side ?

and a bit of confusion with your post re: breather status. theres two types of catch cans, a breather type (open to atmosphere) and a sealed inline type (correct me if i'm wrong) and the breather type between the manifold and the rocker cover would render the 'pcv' completely useless. you would want a breather type catch can on the venting side and an in-line type for the constant vacum side.

the whole system creates pcv it doesn't entail two seperate operations, what your saying is true about relieving back-pressure but it's still only one system. ie: adding a breather direct to the rocker cover on the rear end = same system, less hose, but without the (filtered) vent the pcv would be sucking oil straight into the manifold.

and on the subject of keeping the inlet anifold clean..... it will never happen, it's the nature of the beast. if anything i'd consider relocating the injection point for the gases eg: swapping the brake vacum & pcv lines but then this may cause oil saturation in 6,5 and possibly 4 & a clean 1,2 & 3. (yet to be proven) best system would be 6x1/8" inlets introduced just behind the injectors.

ok thanks every thing you have said is correct , now my problem im looking to get positive cv during wot as this is when the engine will see most blowby ,now my pcv hose runs to my intake custom manifold between the tb and the blower ,clean air to the rear of rocker cover

what happening is im seeing to much vac and coating the inside of the blower, pipes, intercooler etc. in oil

engines good 140ks no real smoke at idle very small wift etc.

cant go other side of the blower, it will see pressure under boost , check valve would close this off but thats when i want the vent

thinking of exhaust , like the moroso kit

xf paul, I am not exactly clear on your setup but from what I cant interpret, it may be setup incorrectly.

You need TWO seperate hoses. The first is the PCV valve that you connect onto your intake manifold. Then you need a second that can be vented to air. (this may be what you have)

If you have higher than average vacum, you will pull alot of oil from the engine if you dont have some sort of filter system

I looked up my VT supercharger manual and it looks like it is setup to run between the intake manifold (under the supercharger) and the tract between the T/B and the supercharger.

They also have an oil seperator thingo included in their PCV valve setup which looks like a usuable thing on other setups.

low ryder,

yes I have two different filter systems. One for the PCV side and another for the other hose.

The objectives are to remove as much oil from the air going back into the engine intake in a bid to reduce emissions, keep engine clean, prevent oil seals getting blown and reduce oil consumption.

We could discuss this for ages but a picture would explain things alot better. Once I get it completely done I will post a pic.

for the amount of oil that ends up in the catch can, i personally think its a waste of time having a return bak to sump. i probably drain mine every 10,000kms and there's stuff all in there

Im a fan of leaving the PCV alone. They work fine for the factory and are designed, as the name states, to provide crankcase ventilation only during times of positive pressure to aid the prevention of blowing seals out.

If you want to, use a catch can after the PCV check valve and before the inlet manifold. Before its full, drain the garbage out of it. If you cant drain it, dont get it.

Some big misconceptions here!!
The PCV is closed when on boost.. Which is different to n/a ..
So while on boost the breather is through the rear vent on rocker cover..
This is better to have oil seperator / catch can on..
Then this is attached to either aircleaner outer cover or inlet between filter
and turbo.. Unless you run a vacuum pump? There is little vacuum in crankcase while on boost...
I find it better to drill the breather on rocker cover much larger than it is..
In some cases the catch can can be low in engine bay.. Say above chassis rail?
Then up into inlet pre turbo.. This helps oil keep in catch can..
What I have done to V8 .. Where PCV comes off manifold I added 120mm alloy tube to lift PCV away from oil.. This helps oil drain back and prevents oil being picked up in first place..

so the pcv is left to the t/b and the hose on the back of the rocker goes to a oil catch can