The PCV System

Feb 26, 2005

1) When the engine is running, a small portion of the gases (which are formed in the combustion chamber ) leak past the piston rings and enter the crankcase. Since these gases are under pressure, they tend to escape from the crankcase and enter the atmosphere. If these gases are allowed to remain in the crankcase for any length of time, they contaminate the engine oil and cause sludge to build up in the crankcase. If the gases are allowed to escape to the atmosphere, they pollute the air with unburned hydrocarbons. The job of the crankcase ventilation system is to recycle these gases back into the engine combustion chamber where they are re-burned.

The crankcase (blow-by) gases are recycled as the engine is running by drawing clean filtered air through the air filter and into the crankcase. As the air passes through the crankcase, it picks up the combustion gases and carries them out of the crankcase, through the oil separator, through the PCV valve or orifice, and into the induction system. As they enter the intake manifold, they are drawn into the combustion chamber where they are re-burned.

The most critical component in the system is the PCV valve. This controls the amount of gases that are recycled. At low engine speeds, the valve is partially closed, limiting the flow of gases. As engine speed increases, the valve opens to admit greater quantities of air to the intake manifold. Some systems do not use a PCV valve. They simply use a restrictor or orifice in the ventilation hose to meter the crankcase gases.

If the PCV valve/orifice becomes blocked or plugged, the gases cannot be vented from the crankcase. Since they are under pressure, they will find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket, it usually creates an oil leak. Besides causing oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period, promoting the formation of sludge in the engine.

2) The PCV system has two things that take place.

First, it lets fresh air into the crank case. It grabs this air from inside the throttle body on the inlet side of the plate. That way it never sees vacuum and the air going into the crank case is metered by the MAF.

Next, the M90 sucks air out of the crank case. There is an opening on the inside of the inlet of the M90 way up in the case that sucks air from the crank case. This air comes from the crank, goes through the PCV valve and then finally enters the inlet of the M90. This is why your rotors and intake get oily.

3)The stock PCV system is left intact with the SS intercooler. There are no changes made to it’s operation with the SS IC. Adding a breather would do the same thing as adding a breather to a car with no intercooler. Drilling that extra hole in the intake manifold will do nothing for you.

3) On the full size ZZP IC the inner core is very large. In fact it’s so large that there is not room to drill all the holes we need for PCV operation straight through it. This is because of this we had to make an offset PCV hole. This is why you have to drill the intake manifold and modify the gaskets with the ZZP core. Once doing that the crank suction part of the PCV operation is not changed, we just relocated the hole slightly. If done properly this functions like stock.
The full size ZZP core blocks the fresh air inlet from the TB, just like the LS1 adapter plate. When it does you have no way of getting air into the crank, and you only are sucking it out (via 1st paragraph of #4). When this happens you get too much crank case vacuum at idle and the car will make a loud squealing noise or possibly suck a gasket in. The loud noise goes away when you take off the oil cap and you can feel air being sucked in there. By installing a breather you now solve this problem. The breather is now taking the place of that crank case inlet in the TB. The only issue here is that the air is not being metered by the MAF anymore so you will need to adjust your fueling slightly at idle (usually adding 1% to MAF freq at idle). This is not a big deal as anyone with a cam needs to adjust idle MAF already.

4) For turbo or CSC guys you are blowing into the TB, intake and engine. There is nowhere to get suction from so the PCV is rendered unusable. These guys run a breather for a different reason than LS1 or ZZP full size IC users. For the aftermarket power adders the breather lets air OUT of the crank case. The exact opposite of what M90 guys use it for. When you go under boost the piston rings leak a bit and pressurize the crank case. This air needs to be let out and the breather does just that. The more boost you run, the older your engine is, or the larger piston ring gap you run the more air that needs to come out. Some of these guys will end up needing to use 2 breathers. These are the guys that you see with oil on the valve covers or steam coming out of the breather.

5) Problems. M90 guys that use the ZZP IC and DO NOT FOLLOW INSTRUCTIONS or M90 guys that run an intercooler that blocks the PCV suction will become #5 guys. In this case your M90 will be acting like a CSC or turbo and you will have steam coming out of the breather or oil all over your valve cover. It is because so many people don’t trim the 2 SC gaskets right; and some people run an intake w/ the relocated hole (the one we drill) that  you read so many of these threads on ClubGP. Confusion is created by people posting different information because their setup is different from someone else’s and they might not even know it.

It won’t damage the car if you run a breather and use it (like paragraph #5). You won’t have the minor idle fueling issue either. However, you will have to deal with a dirty breather and a non functioning PCV system.