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josh817

Crank case ventilation..

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If Braap would be so kind to move the posts from the engine bay thread, we can continue the discussion over here. It seems to contain some good info for those wanting to convert to triples...thanks!

 

Posts moved from engine bay pics thread. .

 

Here's one of my 81 280zx...nothing special..

 

SMN2008067.jpg

Edited by BRAAP

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If it's blocked off and can't vent from both there AND the top of the valve cover, you will build pressure in the crankcase as it heats up and start blowing seals. At least a breather vent - or better yet still - vent to a catch can. That motor looks pretty new, so you might not have experienced it.....YET.

 

Who is everyone? There's a lot of folks on this site that would cringe (as you saw) at that piece being blocked off...it's been discussed ad nauseum in many threads.

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If it's blocked off and can't vent from both there AND the top of the valve cover, you will build pressure in the crankcase as it heats up and start blowing seals. At least a breather vent - or better yet still - vent to a catch can. That motor looks pretty new, so you might not have experienced it.....YET.

 

Who is everyone? There's a lot of folks on this site that would cringe (as you saw) at that piece being blocked off...it's been discussed ad nauseum in many threads.

 

 

Gotchya!! Will remedy as soon as possible. Thanks guys. Just wondering tho...if the oil pan is open to the timing cover, and the cover is open to the head, and the head is open to the valve cover...wouldn't it still be able to vent out the breather? Or am I not remembering that the oil pan is sealed behind the cover?

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I would assume the same but its pretty easy to run a catch tank. I have a vent on mine and it make the manifold so dirty. Mine is like a yellow silver color now. Ebay dudes sell those cheap catch tanks for $20 shipped. Hide the tank under one of the service flap things near the master cylinder, will work out well.

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Or just run it into the intake manifold somewhere, valve cover in front of the throttle plate, crankcase behind the throttle plate.

 

On a triple setup - there IS no place to vent back into the intake. Unless you want to poke a hole in the intake somewhere and fit a PCV valve in there. Hence - the problem as it exists today.

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Regarding Edz280zx choice of crank case ventilation, it sounds like you guys saying that he needs to remove the plug are assuming the crank case is sealed off separate from the valve cover, which it is not.

 

Preferably a PCV valved system plumbed into the intake manifold would be nice, (I am a huge proponent of that system), as it keeps the oil cleaner, affords a little better ring seal, main seals are much less likely to leak, etc, but technically, if you don’t use a PCV system, (which many guys don’t), his arrangement with the core plug in the crank breather is fine. He has a valve cover breather and the crank case is NOT sealed from the valve cover, i.e. they communicate air, (pressure and flow), up through the timing chain cover AND the oil drain back hole in the back of the head/block.

 

In short, if he had a breather tube/filter on the crank case vent as well as the valve cover, the pressures in the crankcase and valve cover would be no different than they are now, i.e. he is not building any more pressure in the cranks case with just the valve cover breather alone. If the valve cover breather was not large enough to allow crank case pressure from blow by to escape and the crank case was building pressure, adding another breather vent doesn’t’ fix the “Real” problem, which would be too much blow by!

Edited by BRAAP

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I guess I didn't put my reply exactly how I wanted it to come across. I meant to state if BOTH the block and valve cover breathers are blocked off - THEN you have a problem. He does have the valve cover breather. But why wouldn't Nissan just have used the VC breather and plugged off the block completely? Both are plumbed back into the intake system. One pre and one post throttle plate. I dunno - they put two holes there for a reason - one would think.

 

Also - I would like to pose this. I have never had my timing cover off and filled the engine with oil. The gap between the front cover and the pan is the "main" way for pressure to equalize (largest opening). Does 5 quarts of oil fill the pan up completely to the bottom of the block such that if you were to pull the front cover, oil would come out of the front of the pan? If so - there's nowhere for pressure to equalize (rear drain included, as it's draining down - not up) - unless you've got enough pressure in the crankcase to push the oil out of the way to equalize. My guess is if you're at that kind of pressure - your front main is the first thing to go. If the oil level DOES stay below the front main cap when full- then you're ok - but like I said - I've never filled the pan mounted to the block with the front cover off, so I honestly don't know. Anyone done this to test?

 

Further adding to this theory - if the oil drainback hole in the back of the head/block is full of oil draining back to the pan, it's also difficult for air pressure to equalize when the hole is full of oil..unless air gets in with the oil. I dunno - I'm not anywhere close to schooled on fluid dynamics - I'm posing questions (probably in the wrong thread) to learn. Should we take this to another thread? Paul?

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I guess I didn't put my reply exactly how I wanted it to come across. I meant to state if BOTH the block and valve cover breathers are blocked off - THEN you have a problem…

Exactly right.

 

…But why wouldn't Nissan just have used the VC breather and plugged off the block completely? Both are plumbed back into the intake system. One pre and one post throttle plate. I dunno - they put two holes there for a reason - one would think.

…

OE, the block breather is plumbed to the PCV valve in the bottom of the intake manifold with vacuum in the manifold, it is drawing air for the crankcase through that valve which is essentially meter air leak. At any rate, it is drawing air from the crank case into the intake manifold, (ever notice the oil residue on the inside of an intake manifold? No you know where it comes from). The tube in the top of the valve cover is plumbed in between the AFM and the throttle body of EFI cars. That is where the air comes from that is being drawn through the PCV system. That air is filter for the intake air filter, and metered for the AFM so the EFI is compensated for the air being ingesting. The factory PCV system is flowing clean filter air from the valve cover down in the cranks case and back into the intake manifold. Keeps the noxious fumes in the crank case down, cleaner oil, yadda yadda yadda. Pretty good system, still being used in that same exact manner on vehicle today.

 

…

Also - I would like to pose this. I have never had my timing cover off and filled the engine with oil. The gap between the front cover and the pan is the "main" way for pressure to equalize (largest opening). Does 5 quarts of oil fill the pan up completely to the bottom of the block such that if you were to pull the front cover, oil would come out of the front of the pan?...

Oil level when full is WELL below the main seals and below the spinning crankshaft which is below the main seals. For learning sake, spinning the crank shaft in oil would add tremendous drag, loss of power. Fill up your bath tub and with your open hand, try to move your hand through the water real fast. Do the same in the air. Imagine your trying to do that at 150+ MPH! Your crank is. I'm sure you have heard the term "Windage" before. IN relation to engine and crank cases, that is the referring to oil and the pinning crank. We try to minimize windage losses as much as possible, freeing up HP lost in spinning the crank through oil splashed about in the crank case.

 

…

Further adding to this theory - if the oil drainback hole in the back of the head/block is full of oil draining back to the pan, it's also difficult for air pressure to equalize when the hole is full of oil..unless air gets in with the oil….

The oil passage that feeds the head/cam is only a small hole, barely larger than the head of a ball point pen! Volume sis, not very much oil actually goes up to the head. The drain back hole in the back of the head is large enough to get your pinky finger wedged in. Not too mention, the front through the timing cover is where most of the oil drain back is any how. At that, the rear hole is large enough on its own that it would never be “filled” with oil, i.e. all the oil that makes it to the head can dribble down through that hole back into the crank case as air is moving back and forth around it, i.e. the oil doesn't plug that drain back.

 

…

- I'm posing questions (probably in the wrong thread) to learn. Should we take this to another thread? Paul?

Good point, yes this really is off topic for this thread. Feel free to start another thread and I’ll move the posts of this discussion over there if you’d like, otherwise I will delete these off topics posts later today. :wink:

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Thanks for confirming what I had originally thought Paul. For what it's worth, if I had the time and money I would fab up a PCV system for the car. But for the small amount I drive the car, I don't think it would be worth it right now.

 

Also..this is not a new motor..it has about 96,000 miles on it. It's actually a 79'.

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I was gonna make a post before the move but didn’t want to contaminate the picture thread... thanks Paul for the move.

 

Now for some questions...

 

We're currently building an L24 for use in my ITS racecar car. In the crank case ventilation chamber there’s a screen that was all gooped up and nasty even after we had the block tanked. What’s everyone opinion in leaving it out? Also with the discussion here it seems as if the valve cover breather is sufficient to evacuate 100% of the positive pressure in the crank case. If this is the case it sounds like my best course of action would be to plug the breather on the block and rout my valve cover to my breather can.

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That's mighty clean for that many miles! Duly impressed I am!!

 

I'm in the process (tonight) of fabbing up my catch tank. I ended up buying one from Pegasus. I have one fitting that should be there when I get home and I can finish the process. I will document it with pictures as well. I'm teeing both the valve cover and the block to the catch tank. Nothing fancy - but rather expensive since I decided to stick with the Aeroquip theme....

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One other point to note on the plugged PCV airway on the block (if I may)...

 

Remember, on a boosted, i.e. turbo motor, whenever the vacuum in the intake manifold is goes positive, i.e, changed to boost for forced induction, the PCV valve is closed, hence effectively plugging the hole that he has plugged.

 

This fact alone should be a clue as to whether or not there were other ways for air to vent from the crankcase.

 

It's quite doubtful that a boosted motor would survive very long if it had no other oil and air passage from the valve cover to the oil pan.

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Cobra...If you can afford it, which it sounds like you can, I'd just do what 2eightyZ4me is doing. $$ is the only reason I didn't do it when I put this setup in my car...this is really a budget car.lol

 

2eighty...I look forward to seeing your install pics as I will eventually be doing something similar in mine....unemployement really put the brakes on a project!! FYI, this motor was vigorously cleaned and then repainted before it went in...that's why it's so purty..lol. Thanks for the compliments tho!

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Well... Im gonna build a rather large airbox around the carbs and seal it as best I can so getting a good vacuum to run a PCV setup will be near impossible, plus Im not too keen on getting oil vapor in my combustion (ever 10th of a HP matters.)

 

With the old motor we just ran both to the catch tank... but if the valve cover breather is good enough for all ventilation, then running one line to the catch can simplifies everything, cleans up the engine bay and even reduces weight (ever little bit helps)

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Well... Im gonna build a rather large airbox around the carbs and seal it as best I can so getting a good vacuum to run a PCV setup will be near impossible, plus Im not too keen on getting oil vapor in my combustion (ever 10th of a HP matters.)

 

With the old motor we just ran both to the catch tank... but if the valve cover breather is good enough for all ventilation, then running one line to the catch can simplifies everything, cleans up the engine bay and even reduces weight (ever little bit helps)

 

True dat;-)

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So the verdict is the block plug is fine as long as the valve cover is vented?

 

 

I’m not 100% convinced of it... I’m not sure exactly how much volume were talking about so IMHO the single valve cover vent COULD be a restriction. So unless someone who KNOWS otherwise posts from experiance (I want one last post from BRAAP)... I’d consider the case still very much open.

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