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WDRacing »
https://forums.nicoclub.com/wdracing-u3125.html
Wed Aug 26, 2009 8:04 am
This is an excellent article that explains the PCV system and the valve itself.
Postive Crankcase Evacuation
Start by reading through that, so you will better understand my opinions on PCV Modification do's and don'ts.
The article mentions that increased mileage on the motor will lead to increased piston blowby. It doesn't mention that increased cylinder pressures also lead to increased blowby. Which means in the best case scenario, you've got at least one factor that leads to increased blowby and two if your motor isn't freshly rebuilt.
Why is that so important?
Because blowby gases contain a bunch of nasty stuff, from unburnt fuel to hydro carbons from the combustion process itself. At best, the combustion process has burnt all of the fuel and you only end up with nasty soot mixing with your oil...that's OK right? No.
Blowby is the #1 reason your oil is black when you change it. So even with the motor running naturally aspirated and the stock PCV System working at 100% you STILL get lots of blowby mixing with the oil. So much so that it turns totally black long before you are scheduled for a change. The oil cleanliness factor determines how fast your bearings wear as well as ALL the other lubricated surfaces in the entire motor. Sounds important when you think of like that huh? It is. Oil isn't changed because it's worn out...it's changed because it's contaminated.
Remember that we:1) Just increased the cylinder pressures across the board by adding a turbo.2) If your motor isn't fresh then you're already venting blowby into the oil. 3) If the tune isn't perfect you're adding increased blowby, in this case it's in the form of unburnt fuel. Adding boost requires the tune to be rich in order to not suffer from knock. Most consider this the "safety margin". It isn't bad in itself because it's necessary for most daily drivers. However, if the tune isn't perfect, you're pumping fuel into the oil.4)Cranked up the load / temperature of the entire motor causing further oil breakdown.
Knowing that, do you still want to take the stock system and weaken it? By that I mean any system or modification to the system that removes vacuum from the crankcase. Obviously we don't like the blowby gases being fed back into the intake manifold. It coats everything with carbon sludge and reduces the effective octane ratio of whatever fuel you'rein using. The next few things are idea's that don't work as well as the stock system. Yes they bypass the recirculation back into the motor, but at the cost of ruining your oil.
Having the valve covers vented to the atmosphere doesn't PULL blowby gases from the sump, it allows them to vent. The venting takes place when the sump fills up with vapor or the heat causes the vapor to rise on it's own. Doesn't sound very effective huh? That's because it isn't.
Having the PCV valve connected to the intake pipe pre-turbo doesn't PULL blowby from the motor. There is NO VACUUM before the turbo. When the turbo is spooled up it does pull quite a bit of air, however, when you're on boost you're also creating the most blowby. You also have to run an air / oil separator in-line so as not to have oil and carbon coat your entire intake tract. But wait, doesn't that just let the gases go back into the intake anyway? Hmm...
Those are the two most common setups that don't work. There are many other options that people have tried, but the fact remains. If you remove vacuum from the sump, you add crap to the oil.
What are our options then?
How about anything the mind can come up with, so long as the sump sees some type of vacuum related evacuation.
I like to keep things simple. So I choose to improve the factory system. I mean why not, it works and it's already in place. What parts can be improved? Well the PCV valve isn't designed for boost, so lets start by either adding an extra check valve that doesn't allow boost to creep past or swapping the stock PCV valve for one that's designed for boost.
The stock air / oil separator isn't ever changed. So lets add a air / oil separator in-line. One that allows us to monitor how much blowby we're actually removing and has changeable filters. I recommend the filters from Home Depot that they use for air compressors. Cheap and easy to install = win. In two simple steps we just increased the effectiveness of the stock system.
Another thing I do is swap oil filters in between oil changes, to cheap and to easy not to do.
Not enough? Want to remove the gas from going to the intake entirely?
You can run a vacuum pump. They can be had in the junkyard for about $40 from any older GM V8. They can be installed where ever because the pump is electric. Simply run an air / oil separator between the PCV valve and the pump and your done. Now you have vacuum even under boosted conditions. You can also buy aftermarket systems that go all the way to $550.
The other thing you can do is run a header mounted evacuation system. They are under $100 but only pull blowby when you're under a load. When idling there won't be enough exhaust flow to create the venturi required to pull the blowby. I also can't say without speculation what rpm and load would be enough to start the venturi effect. I'd use this method combined with the vacuum pump if I wanted the best of both worlds.
Questions?
WD