PCV valve location

[twobjshelbys]

Originally Posted by Tommy

The very nature of gases in an enclosed space and the principle of entropy means that even if there is a momentary local region of higher pressure, it will very quickly even out within the enclosed space. So if the crankcase pressure in one area (e.g., the driver side valve cover) were higher than that in another connected area (e.g., the passenger side valve cover), they would very quickly equalize. With all the blow-by pressure dumping into a common oil pan area, unless there was some system of intentional or unintentional one way valves inside the engine, I can't see how the crankcase pressure would be inherently higher under one valve cover than the other.

Credentials: BA Aerospace Engineering

Everything you say is true. But an engine is anything but a closed systemi. An engine has lots of moving parts that disturb the static environment. I do understand entropy. In fact, I got an A in Heat and Thermodynamics (one of my degrees, there are more).

Let's just say that which side defies intuition based on all of our static analysis. Intuition says that the system should be balanced with equal pressure on both sides. The empirical data supports that one side is suction and the other side pressure. The fact that the 390 (probably a FE) picture has an open cap on one side with no evidence of exhaust and the PCV (pressure) on the other supports that. The same was true on my Windsor with no PCV but with the K&N filters - one side had oil from the inside to outside and the other was dry. And similarly, if both sides were pressure, I'd guarantee you that Uncle Sam would demand PCV hardware on both sides. Noone here understands why it works this way, but the fact remains, it is a fact. It defies logic and intuition. Sorry, I'm not trying to define why it happens, only, from the beginning, reporting my observations. Sorry if you're looking for something beyond that, since you're not going to get it from me.

Also, while other engines may be interesting, the OP was asking about Windsors. It is consistent with my catch-can observations on my supercharged Shelby GT which was the 4.6L 3V modular combined with others that have put catch cans on both sides and observe they never "catch" anything.

So the message to the OP is: Leave the PCV where it is.

I'm not sure the consequences of changing it would be pretty: As configured, minute amounts of oil but certainly some amount of pressured gasses go from the engine to the air intake. I don't know the volumes or pressures involved. If you reverse the configuration all of a sudden the suction/vacuum side will pull stuff from the air cleaner area to the top of the engine. Think about it carefully. Then try it if you feel lucky but please report back here.

I still think Brent is the only one that can explain it. I'm not going to try to solve it myself. I'm no longer interested in investing research and learning for something that I will only use once, 20 years ago maybe, but not now. My brain is full. I'll look for an expert to explain (similar to drywall, there are experts that can do that).