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One of my latest projects is to set up open crankcase ventilation, and when taking a look at the system, the stock ventilation is highly inadequate for a truly well ventilated system.

However, what my theory is is that these engines were built to, lets just say not very exacting tolerances (compared to Honda for example). Knowing this, and knowing blowby/windage would be high, Nissan restricted how much the PCV system can flow to provide oil consumption levels that are acceptable to the average consumer, and reduce excessive oil going through the manifold and reducing plug life and causing premature deposits. If you open your oil cap when one of these motors is running, there's tons of blowby, it's ridiculous. The fresh air inlet (the hose running off the intake to the valve cover inlet) on the valve cover has an orifice in it, it's much too small to provide adequate ventilation, same goes for the PCV valve, too small. If you take that hose off during running you'll see positive pressure tries to come out of it like a garden hose.

What i will be doing is running an open setup. This involves enlarging both the PCV port and the fresh air inlet to as large as i can get it, and plumbing those two ports to a catch can ventilated to atmosphere (it could be plumbed back into intake if you care about emissions). As i said you could plumb it back into manifold vacuum, but i want to completely eliminate ANY oil vapors from getting into my intake/heads/combustion chamber etc.

As to why i think this is related to the engine failures we have seen. Well, when you have inadequate crankcase ventilation for a given amount of blowby (in this case a large amount of blowby), you get alot of oil dilution since the windage condenses in the motor and the sump (made up of various elements, acids, and raw gasoline), which is fine, if you adjust your oil change intervals accordingly (i change mine every 5000KM, which apparently is abnormally frequent compared to many people on here), but most drivers (no offense intended) don't check their oil regularly (or don't know what to look for) and drive and drive and drive.

I think with more adequate ventilation a small performance increase could be measured as well.
 
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