PCV Flow Direction - Can I Reverse?

[Zed Head]

2 hours ago, Captain Obvious said:

The original purpose of this thread was to entertain the idea of reversing the default flow direction of the whole system so the "reversed" direction of that upper tube would become the "normal" direction instead. This would also mean that the block connection under the distributor would become the fresh air replace except under high blowby conditions.

One improvement I could see from reversing flow would be the ability to clean the "steel net", that you would be adding if you matched the system design, in reverse.  I think I've mentioned this in other threads but we used to build mufflers for our vacuum pumps in chemistry lab so that the exhaust vents wouldn't blow oil vapor.  We packed a piece of pipe with steel wool, just like you show in your post, and attached it to the vent.  Without it, there would be a steady oil mist whenever we pumped a vessel down.

But in order to match what Nissan has you'd need a very large filter/separation chamber on the valve cover side.  More than just a flame arrestor sized piece.  Might be bale to build one inside the valve cover.

To take the geekiness in another direction, it would be nice if the steel net in the block had easy access so that it could be removed and cleaned.  I imagine that as it gets gunked up over the years, it loses surface area and becomes less effective, letting oil vapor pass through.  Could be why some old engines end up with a lot of oil in the intake manifold.  My old 76 engine was wet with oil in the intake.  You'd have to cut a whole in the side of the block though, or add a filter box to the end of the pipe that goes to the PCV valve.

[Zed Head]

Here's an 81.  It looks just like a 78 that I also have.  carpartsmanual shows a change in the L24 engines but doesn't give a year.

Sorry to get the thread all oily.  It's just a spare engine.

 

[Captain Obvious]

Thanks for checking Zed Head, and thanks for the pic of the 81 cover.

Chickenman, I know the stock system works well. A little ashamed to admit it, but the only reason I've even entertained this idea is simply aesthetics. Here's my thinking... I've got a FI car, and currently the PCV valve screws into the underside of the intake manifold. If I were to relocate the PCV to the engine side of the intake manifold (instead of the bottom), then I could connect a short tube from the valve cover to the relocated PCV valve*. That tube wouldn't even have to cross the fuel rail. It could go under/behind the fuel rail instead.

Then for the block end connection, I could run a short piece of tube from the block to a nipple on the underside of the rubber intake boot that connects the AFM to the throttle body.

The whole thing would be so much cleaner and simpler than the existing system. I wouldn't have those long large PCV tubes running across the top of the engine all the way from the valve cover up to the throttle body.

* As a side note, there's even a threaded hole (plugged with an allen headed plug) in the intake manifold down between the runners for cylinders 3 and 4. It connects into the shared internal passageway for the EGR system. It's almost as if Nissan had considered exactly what I'm suggesting.

From this old thread  http://www.classiczcars.com/topic/22366-efi-progress-on-my-datsun-240k/  here's a couple pics of the integral EGR passageway built into the intake manifold. This one is webbed (which mine is not), but the concept and location of the passageway is the same. He's removing the EGR passageway completely to clean up the look of his intake manifold:

 

In this pic, you can see the flat boss cast passageway between 3 and 4. The boss was never drilled and plugged like the earlier ones were though. But the boss still exists:

 

 

Edited July 14, 2017 by Captain Obvious

[Zed Head]

It wouldn't be as clean and neat on the inside but a person could run a tube to the area of the exit port under (above) the baffle then run the tube to wherever they wanted the new exit to be, inside the cover.  You'd have the same design that was originally engineered, except for the volume that the tube occupies.  If the multiple bends in the baffle have a function it would be maintained.  

[Captain Obvious]

I had to read what you wrote about six times before I figured out what you were talking about.

Just in case it wasn't just me having troubles... What Zed Head is suggesting is that it would be possible to cut a hole in the stock baffle plate and then connect a tube to that new hole. Then you could also cut a hole in the valve cover anywhere you want, and bring the other end of the new tube out that hole. The end result would be a stock baffle performance, but you could relocate the exit hole anywhere on the valve cover surface.

Assuming there's room inside to run said tube without it interfering with the camshaft or valve train.

[Zed Head]

I did leave the thought a bit unfinished.

When I look at that stamped piece of steel, that only covers half of the length of the cover I think that some engineer somewhere (probably at Nissan Motor Corp.) must have put some time and effort in to it.  Can we really just throw it all away?  Save some of it.

Is there a purpose to those bends and that shape?

[Captain Obvious]

Yes, I believe the shape of the baffle with the bends has a purpose. It's intended to seal the baffle around the entire perimeter except for the very back corner where it's open. Presumably, the designers thought there would be the least amount of oil spray flinging around back there.

Then the bumps and valleys in the middle (in conjunction with the cast ribs on the inside of the valve cover) force that air to swim a crude labyrinth (up and down) in an attempt to separate the liquid from the vapor. Up over the baffle bulge, down under the cast rib. Twice. Before finally getting to the hole at the very highest top part of the valve cover where gravity should also help keep liquid inside while allowing vapor to pass.

I wasn't there when they designed it, but that's my read.