Questions reg. air/oil separator on Z24 turbo build.

[Spiff]

Since there is a crank breather and  rocker cover breather do I:

A- Buy two catch cans and plumb one into each of them and then to the intake

B-Buy one catch can with two inlets and one outlet or

C-Buy a regular catch tank and connect it to the crank breather and let the rocker cover breather vent to atm or put a breather filter on it.

D-Same as C but "T" the crank and rocker breather together before the catch tank.

 

I feel A and B does the same thing, and cost wise is about the same as well. Astetic reasons would put B over A, less clutter in the engine bay

C is definately the cheapest, but the breather filter on the cover isn't legal here and it always leaves a oily film that dust and grime sticks to around the breather in my experience.

D; Cheap as C but without the grime and it keeps the emissions bit kind of legal. Only thing I can think of is airflow? Two 5/8 lines combining would need an even bigger line going to the can? Or is this not something to worry about? 

 

PFA ?

[DanielC]

Why no PCV system?

[Spiff]

33 minutes ago, DanielC said:

Why no PCV system?

 

Want the cleanest possible air going in to the engine. 

 

So I've been browsing Hybridz.org for a while now and it seems most people either go for alternative B or D either plumbed back to turbo inlet or venting to atmosphere. 

[datzenmike]

The PCV uses a small amount of intake vacuum to draw fumes and moisture from the crankcase into the intake and burn them. The air that is removed from the crankcase is replaced with filtered air* from the air filter. Under heavy load, the vacuum is low and the blow-by gasses may accumulate and back up and reverse through the valve cover and into the air filter where it is sucked into the intake and burned harmlessly anyway. The system is simple and fool proof no catch can is needed. The Z18ET would have been plumbed this way. Why do people insist on messing this up? Catch cans are for real race cars (may even be mandatory on some tracks) that may blow an engine or have a failure that would otherwise blow/spill oil on the track from the block or valve cover vents.  

 

* filtered air don't get any cleaner.

 

A... does not circulate any fresh air through the engine at all, only catches blow-by (if any)

B... exactly the same as A

C... Again no air is drawn through the engine., worse than A or B

D... Again, there is no exchange of fresh air for what leaves the engine.

 

Catch cans are useless for anything but race cars that are required to have them out on the track. If you are blowing oil out the block vent or the valve cover vent then you have bigger problems.

[Spiff]

All engines have blow-by to a varying degree, some more than others, and turbo engines experience more blow-by than n/a engines.

Blow-by gas contains a foul mixture of oil vapour, unburnt fuel, co, nox, and other acidic gasses which can lower the octane of your fuel. 

Furthermore oil vapour will condense and coat the insides of the intake, throttlebodies/runners and intercooler(s)(reducing efficiency of ic). Also leads to carbon buildup in DI engines.

Plumbed back to the (turbo) inlet there will be a slight vacuum present in the crankcase, this helps rings and seals to seal better, improving performance.

 

All of this is facts, simple as that. You say a catch can is useless on anything but race engines. I disagree, the LS engine f.ex has been known to consume oil, fill the intake with oil etc because of a poor pcv system. The simple addition of a baffled catch can or other air/oil separator has been known to cure this. Audis tfsi engines as well suffers from badly engineered pcv systems and some bmw engines.

 

Had this been a stock engine, sure no problem, run the factory pcv.

But this z24 is not a stock engine, it's not N/A and I will be pushing this to the limit and probably beyond hence I wan't the air entering my engine to be as clean as possible with as little variables as possible.

[datzenmike]

Leave the block vent connected to the PCV as usual. Under no boost conditions there will be almost no blow by and fresh filtered air will circulate normally through the crankcase extending the oil change interval. Under boost, the intake will pressurize and the PCV valve will be pushed closed, so nothing from the block can enter from that direction anyway. The valve cover vent? run a hose elsewhere (like down beside the block and vent under the car) and put a filter on the end. Or a catch can so it doesn't drip all over. But now you have to dispose of this waste water/oil/petroleum. If you plan to just throw it in the landfill garbage, you might as well let it drip under the car so why collect it? Under boost, the crankcase blow-by pressure (slight though it is) will vent out through the valve cover and not into the intake at all.

 

Datsun Z series engines are not known for excessive oil consumption and there is nothing wrong with their PCV systems that needs a catch can to 'fix'. The block vent is well screened and baffled as is the valve cover high on the engine which gives plenty of time for any oil fog to separate from the air. A windage tray or crank scraper would reduce it even further in the first place.