How Do You Properly Run An Oil Catch Can?

[duffymahoney]

1 minute ago, AK260 said:

Wouldn't the block pressurise and create oil leaks everywhere? 

I think it would just go out the valve cover?  I have no clue.  

[AK260]

4 hours ago, duffymahoney said:

Ok, here is my plan. It's a bit complex.  

 

Some pcv grommet from a multi pack, fits the stock check valve and block perfectly.  I might end up moving this upstream, I am a little afraid of it getting oil trapped in it.  Then BSPT adapter to hose barb.  Hose barb to a true air filtering catch can.  Catch can will be a billet version of the mann provent 100 or 150.  Filter media gets 93% of particles prior to hitting my intake.  I plan to change the filter every 1-2 oil changes.  It will mount to existing 240z holes on the fender.  Then from the filtering catch can, to the intake.  This is all just for the lower block PCV.  I haven't decided what to do about the valve cover one.  

As much as I commend the creativity of this solution, something in the back of my head is nagging me that the PCV valve is going to clog up over time! *Scratches head, removes even more vitally needed follicles*

[Av8ferg]

So here’s a question. Duffy has the PCV valve coming directly off the block. Are you going into a catch can inlet from there? Would the line off the valve cover go not the other inlet of the catch can? Outlet to a filter mount on the top of the catch can?


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[Reptoid Overlords]

I’m sure someone on the forum will chime in that knows how to refit this.  I can’t be the only one that has this problem.  I imagine you can put a sleeve in there and re-press it in.  Maybe an epoxy weld like JB weld might work too.  I’d rather have a better solution that that.  Any thoughts on the PVC delete for EFI catch can.  Captain Obvious might have an answer for us.  

I used Toyota black FIPG(form in place gasket) on mine.

It's holding fine after 1,000 miles at least, and the PCV system seems to be functioning fine.

I'll bet that if I went and pulled on it with a bit of force it would break the seal though.

[AK260]

A good read on the first two paragraphs ...

https://www.burtonpower.com/tuning-guides/tuning-guide-pages/engine-breather-system.html

[Captain Obvious]

8 hours ago, AK260 said:

Datsun Spirit provide engines without them being in place - so worth dropping Eiji a note at how he recommends going about it.

When you say he provides engines without them (the block breather tube) in place... Are you saying that his engines (as delivered) just have the breather hole hanging open with no tube installed, or are you saying that he actually blocks off the hole with a plug of some sort?

[Captain Obvious]

10 hours ago, Av8ferg said:

Bruce., Thanks for the explanation and that make perfect sense. So keep the PCV in place to balance the vacuum pressure. I’m think the catch can can accept oil in either direction but not sure. If you had 2 inlets to the can that would function the same I think except you might suck oil back a when vacuum pressure is high in the intake. Since most modern cars using catch cans these days are EFI, I imagine there is an off the shelf solution that considers all the changes in vacuum pressure within the intake. I’ll begin my research and report back my findings.

Newer cars have MAP sensors, AFM's, TPS sensors, and O2 sensor feedback. Using all of those tools allows them pull out of one block vent through the PCV right into the intake manifold while venting the second block vent back to the air cleaner in front of the AFM.

Problem is that on our early (much more crude) EFI cars, we had only one of those input sources (the AFM)*, and we have no feedback system (O2). The whole system operates on "assumption". Assumption that everything is working as designed because the ECU module has no way to know or tell if it isn't.

So if you pull from one side of the AFM without balancing it with the replenishment source being pulled from the same side of the AFM, things get out of whack. And there's no feedback source of info to account for it, and no computer to learn from it.

 

* We do have a three position TPS, but that three position switch won't do anything to help with PCV details. 

Edited July 30, 2021 by Captain Obvious
more detail

[AK260]

When you say he provides engines without them (the block breather tube) in place... Are you saying that his engines (as delivered) just have the breather hole hanging open with no tube installed, or are you saying that he actually blocks off the hole with a plug of some sort?

So here’s a recent DSI engine pic below.- he doesn’t block them.



I’m not convinced by the suggestion that if you block it, the fumes would just come out of the top. Why would Nissan and other manufacturers have gone through the trouble of putting vents at the top and off the block? But I don’t know enough about how sealed the bottom is from the top to have an informed opinion.

And here’s a novel approach by [mention=32065]jonbill[/mention] - I love the no nonsense mindset! But maybe he can shed light on how he fixed it to the block.

[grannyknot]

2 hours ago, AK260 said:

I’m not convinced by the suggestion that if you block it, the fumes would just come out of the top. Why would Nissan and other manufacturers have gone through the trouble of putting vents at the top and off the block? But I don’t know enough about how sealed the bottom is from the top to have an informed opinion.

I agree, at times air is drawn in through the valve cover vent and that would be difficult if there is always the positive pressure from blow by from the bottom end. 

[Captain Obvious]

4 hours ago, AK260 said:

So here’s a recent DSI engine pic below.- he doesn’t block them.

Gotcha. So he's assuming you (the purchaser) will do something appropriate with that crankcase vent and NOT leave the vapors in the block.  @duffymahoney 

[Captain Obvious]

4 hours ago, AK260 said:

I’m not convinced by the suggestion that if you block it, the fumes would just come out of the top. Why would Nissan and other manufacturers have gone through the trouble of putting vents at the top and off the block?

The top and bottom are not sealed at all. There are huge holes between top and bottom at both the front (where the timing chain lives), and the rear where the valve train oil drains back down into the oil pan. Top and bottom are in no way sealed from eachother.

The point of the two vents is that you are supposed to have positive crankcase ventilation (PCV) under all operating conditions. With just one vent hole (located at either top or bottom) you could vent off the blow-by, but you would not be able to completely remove the vapors from the block. By having two vents, you can set up a circulatory path and actually refresh the air inside the crankcase with fresh clean air. This enables you to do more than just vent off the excess... It allows you to evaporate off the water vapor and more thoroughly remove any corrosive blow-by gasses.

[Captain Obvious]

Oh, and forgot to mention... Since you're trying to create a complete path that clears out the entire engine interior, that's why the two vent connections are so far apart. If they were both on the valve cover, you would set up a little circle there. And if they were both on the block, you wouldn't clean out the head area. They put one on the head and one on the block so it pulls through the entire block.

On "V" style (and opposed) engines, you can put one vent on each valve cover because they are each joined to each other through the block cavity. But on the inline engines, you need one at the bottom and one at the top.