Post by
mdb4879 »
https://forums.nicoclub.com/mdb4879-u186863.html
Sat Aug 18, 2012 2:27 am
Are you trying to set up your PCV system like the stock FWD CA16/18DE? I'm just curious because you mention the block in the system in stock trim so I didn't know if you were using FWD cam covers or what.
I don't really want to turn this into another huge debate, especially since I'm a novice on PCV systems and you really seem to know a lot about it, TheMan, but I have to disagree with you on the not teeing the covers together things. Reason being that I recall when I was having trouble understanding how to set up a catch can you pointed out that on most other motors, such as SR's, there is only one valve cover and multiple nipples on it, so rather than thinking of how the CA has an exhaust side and intake side cover, just imagine it were one big cover. That being the case whether you have two hoses go to separate locations in the system or you tee them together is irrelevant because they are essentially tee'd together through the valve cover. I agree the shouldn't just go to a catch can with a breather, but I can only imagine that if you tee them together to go to a single catch can then have either two outlets from the catch can or one outlet that you tee into two hoses again and have them go to their respective areas of the system (one to the PCV valve on the intake and the other to the pre-turbo intake plumbing) then everything should function normally. I can only imagine the reason the lines are separated from the factory is because it resulted in less plumbing and possibly better flow without using huge hoses.
As I mentioned before, the entire ventilation system is connected though the valve cover(s) and crankcase. Any time there is pressure, positive or negative, that pressure is seen through the entire system and creates a flow. Under negative pressure the PCV valve will close and the vacuum in the crankcase will be displaced by the relative positive pressure being fed in through the connection to the suction pipe. Under near zero pressure the crankcase will flow and vent through both the intake manifold via the PCV valve and through the suction pipe. Under positive pressure and extreme bursts the PCV valve will close again (in the opposite direction this time) and the flow will be directed out through the suction pipe where there is a relative negative pressure.
Since everything is connected to the crankcase it doesn't matter where or how many times you connect the two hoses together because collectively the system is one entity and shares a single volume. For all it matters rather than having the hoses imagine it were just one big box with a PCV valve in it a part of the suction pipe in it. The system pressurizes as a whole and flow is created because of the difference in pressure outside of the system.
The only other thing I have to say about teeing the two hoses together is if you do the single hose it become must be able to flow just as well as the two hoses connected to it combined. I would just use the surface area of the inside diameter to determine the size of the new hose. For instance, if you had two hoses each with a 1 inch ID then add those together and the surface area of the ID of the new single hose must equal that. 1^2+1^2 = 1+1 = 2 So the new hose needs to have an inside diameter of the square root of 2, which is 1.41 inches (I disregarded pi because it was a common factor for all the equations and was negligible). Then when you tee the single hose back into two just use the original size hose for each. This may only be useful if you are trying to implement a single catch can tied to both the intake and exhaust cam covers. If you are not using a catch can then I see no need to tie them together because they will only have to be tee'd back into two lines. So with a catch can leaving them separated would be the way to go.
