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Positive Crankcase Ventilation System (PCV)

The positive crankcase ventilation system exists to relieve positive air pressure from the crankcase. Pressure in the crankcase is created by piston ring blow by and by the up and down motion of the pistons (just as the piston seals the top of the combustion chamber it seals the bottom of the cylinder, pulling air in on the compression and exhaust stroke, pushing air on the intake and power stroke). In order to relieve this pressure, a vacuum pressure sucks the pressure out of the crankcase through the PCV system. If the pressure is not vented piston ring and piston ring land damage can occur from the rings being jostled around as the piston is drawn down towards the crankcase, fighting against the pressure. In a turbo application this system must be modified or it will not work. Before figuring out how to modify the system it is a good idea to see how the stock system works. Below is a diagram of the stock PCV system:


As you can see the system begins in the intake pipe where air enters a hose that is attached to a barbed fitting on the valve cover. It is important to realize that the fitting on the valve cover is the PCV system inlet, air goes into the valve cover here. The air flows down through the head and into the crankcase. Once in the crankcase the air will pick up oil vapor from the oil being slung around at high velocity by the rotating assembly. The air then flows through the 'breather chamber' which is the black box you see on the back of the block under the intake manifold. The breather chamber has baffling in it that separates out some of the oil vapor and allows it to drain back into the crankcase. A hose connects the breather chamber to the PCV valve. The PCV valve is a one way valve that is open when a vacuum pressure is applied to the top of the valve. The PCV valve is connected to the intake manifold with a hose. The intake manifold exerts a vacuum pressure on the entire system. The PCV system is a closed vacuum circuit with pressure being exerted on one end and vacuum on the other. This allows any positive pressure in the crankcase to be vented.

The problem when a turbocharger is added is that the intake pipe and intake manifold become pressurized. If the fitting on the valve cover is still connected to the pressurized intake pipe it will pressurize the crankcase too. At the same time, the PCV valve will close when pressure is exerted on the top half of the valve, sealing the crankcase. If no modifications are made to the system a pressurized and sealed crankcase will occur when the boost kicks in, this is the worst possible time to have a sealed and pressurized crankcase.

There are quite a few different opinions on how to plumb the PCV system for a turbo application. As long as the crankcase is not being pressurized by the intake charge pressure and the crankcase has some way to vent pressure you'll be in good shape. Probably the worst thing you can do is to add a valve cover breather filter to the fitting on the valve cover and retain the plumbing for the stock PCV valve. This would force the crankcase to vent through the valve cover breather filter. Many of the popular turbo PCV options include the use of a catch can. The catch can has internal baffling that separates out more oil vapor from the system. This is important because oil vapor effectively lowers the octane rating of the gas you are using, making detonation more likely. The catch can of choice is the Moroso Dry Sump Breather Tank Moroso part# 85470. The catch can needs to have 2 fittings on it. One is provided by way of a port on the side of the can. The other must be added by inserting a grommet into the top of the can (Help! PCV Grommet # 42048 for a Ford Econoline Van), and then a barbed fitting into the grommet.
 

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Yes you need to run a catch can to release the Positive Crank case pressure PERIOD.

Your pressurizing the block when you run boost, so in order to release that pressure you run a catch can with open breathers or design a closed system like the toyota supras have stock... to do that you want to run a one way high pressure valve.. but i don't recommend it.. open breather ftw

Honestly OP This is standard stuff when your boosting an N/A motor bruh so some research.
 

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Even on the smallest turbo setup(greddy 15g, or dsm t-25) definitely run one.... its a small investment which will pay off for you in the long run...
 

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Is this a race car or a DD?

A catch can is not necessary on a daily driven boosted D. I will oppose a previous post stating that the worst thing you can do is add a valve cover vent filter and say it works fine. Like the intake air filter, keep it in good shape and it will protect your engine fine. 95% of the time the engine is running in vacuum. The stock pcv will work when routing the hose directly to the manifold. That's it.

If a boosted race application, then a catch can is best.
 

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Is this a race car or a DD?

A catch can is not necessary on a daily driven boosted D. I will oppose a previous post stating that the worst thing you can do is add a valve cover vent filter and say it works fine. Like the intake air filter, keep it in good shape and it will protect your engine fine. 95% of the time the engine is running in vacuum. The stock pcv will work when routing the hose directly to the manifold. That's it.

If a boosted race application, then a catch can is best.
Yes but for the price of a catch can.... its almost dumb not to have one... its not a super expensive luxury add-on... couple hundred bucks at most and done.... yanno? Especially if you are going through all the steps to boosting(parts, labor, tuning). It just makes sense to complete it with a can.
 

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Boost=positive crankcase pressure which needs to be vented with a catch can.

And not to mention you can put a catch can on for next to nothing
 

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Is this a race car or a DD?

A catch can is not necessary on a daily driven boosted D. I will oppose a previous post stating that the worst thing you can do is add a valve cover vent filter and say it works fine. Like the intake air filter, keep it in good shape and it will protect your engine fine. 95% of the time the engine is running in vacuum. The stock pcv will work when routing the hose directly to the manifold. That's it.

If a boosted race application, then a catch can is best.
If you want to keep the system closed its best to use a one way high pressure valve to keep the boost out of the crank case like i said above.

Running a stock PCV system is asking for problems like oil leaks, blown turbo seals.. Not to mention one dirty ass intake manifold lol

Another positive that comes with running a catch can is all the crap it usually catches is water vapor with a mix of oil.

do you really want that cycling back into your oil and degrading it faster??

I run t-6 rotella and after 3500 miles my oil is still see through..

My motor N/A with the stock pcv system after 2500 miles my oil is black..

There are too many good reason not to run one. :TU:
 

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If it were me, Id run vented...

Unless your in an emissions enforced state. then you have to keep it closed.
 

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If it were me, Id run vented...

Unless your in an emissions enforced state. then you have to keep it closed.
who says you have to keep it closed if you live in an emissions enforced state.

Any turbo setup on a honda in a state that requires emissions is illegal period.

That being said why run it closed when the rest of the setup wont pass inspection lol Just sayin

I would run it the best and most efficient way period screw emissions.

emissions is just a scam anyways.. by now most of the cars on the road are LEV so its pretty freakin pointless to even test those cars.. yet people still have to pay for it. Emissions is just about money at this point.. so F em
 

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who says you have to keep it closed if you live in an emissions enforced state.

Any turbo setup on a honda in a state that requires emissions is illegal period.

That being said why run it closed when the rest of the setup wont pass inspection lol Just sayin

I would run it the best and most efficient way period screw emissions.

emissions is just a scam anyways.. by now most of the cars on the road are LEV so its pretty freakin pointless to even test those cars.. yet people still have to pay for it. Emissions is just about money at this point.. so F em

I dont live in one of these states.. but venting oil vapors to atmosphere isnot in the emissions guidelines..IDK how strict they are.. I do know the PCV design sucks ass and only used for EPA laws. Thus making a vented can optimal for keeping things clean and relieving pressure.
 
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