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L20b PCV / crankcase ventilation question


AZhitman

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Built L20b with dual DCOE Webers... Has the crankcase vent tube and valve cover vent in place, but not yet connected to anything.

 

I originally had intentions of plumbing these into a vented catch can to keep any nastiness out of the intake (car will not be driven a ton, so there's gonna be some vapor and "warm-up" crap I'm sure)...

 

However, after reading some posts by DatzenMike has me rethinking that plan.

 

What do you guys have in place?  I'd prefer not cycling any fumes / blowby / vapor into the manifold if I can help it - OR, am I way off here?

 

BTW, I'm not interested in anything half-assed on this car or this engine, so leaving the ports open or slapping some old garden hose on it isn't an option.  :)

 

Thanks guys!

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If it were mine, I would figure out a way to hook up both manifolds to a small balance tube, with a fitting to take a PCV valve for a similar sized engine.

The fumes/blowby/vapor is pretty much mostly unburnt gasoline.    

 

Besides a functioning PCV system will, help reduce oil leaks, because the crankcase operates at a slight vacuum most of the time.

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Hitman! Remember that on your RL411s the "PCV" is connected outside the intake air filter? That's the trick. Connect the PCV to the intake air filter housing before the filter so that the crap gets trapped by the air filter [not shoved into the manifold where it screws up SU needles]. Datsun roadsters and RL411s figured this out almost 50 years ago. Hope your wagon filter is still holding out, flip it 180 degrees about the intake asembly axis to get more life out of it.

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Positive Crankcase Ventilation is your friend, and "road tube" or anything like an open crankcase is not smart - IMHO.

 

It's not just a smog thing, it really serves a good function.  The fumes in your crankcase often contain unburnt fuel, the more blow-by you have at the rings the more unburnt fuel you'll have in the crankcase as the piston pushed that air/fuel mix into the crankcase.  In the old days before PCV there would be a "road tube" to allow the pressure to escape, so you don't blow seals and such, because with blow-by you get pressure in the crankcase.

 

Positive Ventilation means it's sucking those gasses out, and that's a good thing.  Those gasses, with unburnt fuel, will wash away the oil protecting moving parts.  Most common problem, in the old days of "road tubes", is wrist pin failure but other parts suffer too.  It might look "old school" or cool to have a filter hanging on that valve cover breather, but it' doesn't look smart to folks that know better.

 

I don't 'get' the little blue filter either.  Under acceleration the blow-by exceeds what the PCV can handle and it blows out the blue filter which does two things... it plugs it up often dripping oil or the fumes get in the cab. For the price of a blue filter you could run a proper hose into the air filter housing (behind the filter) and the carb would suck it all up. Gee how hard is that.

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I get the purpose for it and I understand the "need" to ventilate the crankcase - I'm asking the best way to go about it.

 

I'm not looking to simply slap a breather on the valve cover, that's for sure.

 

I'm running a Cannon manifold, and was hoping to avoid punching holes in it.  

 

No air filter housing, Mike.  I'm running velocity stacks with individual filters (this is on my '68 Dime).

My thinking was, to keep anything that's not fuel or air out of the intake charge - No reason to reduce octane or send that stuff into the combustion chamber if I can help it (or am I way off here?)

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Ok, so let me make sure I understand:

 

The crankcase port should be plumbed into the intake because it NEEDS to have vacuum?

 

And the valve cover port can simply be vented atmospherically?  Or should it tie into the intake as well?

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If your not going to use a PCV valve, and are going to vent the block to the atmosphere, I see no reason to have a valve cover vent, since there is no PCV valve, which only is able to suck so much in anyway, they put the valve cover vent in to release the rest of the pressure into the airfilter assembly.

Since you are not going to have either the PCV valve, or an airfilter housing to pipe the excess pressure into, I would delete the valve cover vent, and figure out a way to vent the block to some kind of catch can out of sight under the vehicle that has no back pressure.

Keep in mind that your oil will not last near as long, and will look ugly fast, and your engine WILL wear out faster.

 

I could be way off here, but this is the only thing that makes sense to me in this situation.

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I always thought of the port on the valve cover as the intake of clean filtered air, and the PCV as the outlet. If you are going to be sucking bad stuff out, good stuff has to have a way in if it needs it. Isnt that why the valve cover is plumbed to the air filter? For circulation?

Seems there is a diagram that shows the direction of flow.  

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I always thought of the port on the valve cover as the intake of clean filtered air, and the PCV as the outlet. If you are going to be sucking bad stuff out, good stuff has to have a way in if it needs it. Isnt that why the valve cover is plumbed to the air filter? For circulation?

Seems there is a diagram that shows the direction of flow.  

 

I suppose that the valve cover vent works both ways, it sucks and blows out, but the engine case vent also works both ways, but one thing I don't see happening is the the valve cover sucking in, and the block vent pushing out, as they are the same cavity.

He is not going to be using a PCV valve, so the whole thing isn't going to work the way it's supposed to.

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Ya sorry. I have a concern about sucking oil vapor down the intake as well. On stock stuff, what the Hell. But on hot rod stuff, it seems like your going backwards. Also with more displacement and higher RPM's, is the stock system enough? Dont know.

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This is what I ran last year, and it didnt work very well. The oil got dirty quick. There is the stock steel tube welded to the bottom of the can and it wraps around the back to the block vent. 

 

EricVideosbyDave7_zps34a02d24.jpg

 

 

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This is what I ran last year, and it didnt work very well. The oil got dirty quick. There is the stock steel tube welded to the bottom of the can and it wraps around the back to the block vent. 

 

EricVideosbyDave7_zps34a02d24.jpg

 

So you did not use a PVC valve either, and that would be why your oil gets dirty fast, as there is no fresh air getting in the block, and nothing to get the moisture out either.

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Ya sorry. I have a concern about sucking oil vapor down the intake as well. On stock stuff, what the Hell. But on hot rod stuff, it seems like your going backwards. Also with more displacement and higher RPM's, is the stock system enough? Dont know.

 

They use the exact same PCV for an L28.  So unless you've managed to punch a 4-cyl out that big, I don't think volume is an issue. That being said, the system was designed for street use.  For an actual race car, moisture and acidification isn't an issue since the oil usually gets changed before every race.  It's not in the engine for 3+ months and 160+ heat cycles.  If you're REALLY worried about oil mist in the intake, you run a combined Catch Can/PCV system.  The catch can catches the oil that comes up the tube, and an extra set of baffles or screens keeps any oil mist from making it back to the intake, though blowby gasses will still go into the intake.

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So you did not use a PVC valve either, and that would be why your oil gets dirty fast, as there is no fresh air getting in the block, and nothing to get the moisture out either.

 

 

Correct. Both ports just vented into the tube. It had no direction of flow. I change my oil every 10 passes.

 

Silky, thats a nice set up. Thats the way to go for a street set up. The pic I posted on the other PCV thread is my version 2.0.

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At idle and low to moderate speeds with light/mediun throttle, and manifold vacuum, the intake draws fumes from the crankcase through the one way PCV valve. To replace the air removed, the valve cover also has a vent hose to let air IN. This make up air is cleaned by the carb air filter and is drawn through the motor flushing out fumes and water vapor.

 

At high speed heavy throttle or on worn out motors with lots of blow by and burnt oil fumes, the PCV valve is overloaded and excess fumes back up and reverse direction through the valve cover vent entering the air filter housing and are sucked into the carb and burned. The valve cover also has a baffle to reduce oil droplets being blown out into the carb.

 

A good motor will not have a lot of blow by nor will it gum up the carburetor with oil fumes. Cars have been running PCVs since the early '60 and they run just fine with them. If that little blue filter is dripping oil or If you have oil spray inside your air filter making a mess, then you have other problems. No street car with a PCV system needs a catch can any more that it needs a spoiler or a hood scoop. If you have one and have to empty it you have either too much blow by and/or your burning too much oil. 

 

 

If racing, a PCV has no real value. High RPM and full throttle is going to produce lots of blow by and oil spray so why run it through the motor? A catch can is usually mandatory to catch any escaping oil drips and from sudden engine failures.

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I have done this setup many times. It doesn't hook to any PCV vacuum, but it doesn't go straight out either, it circulates.

 

IMG_3086Small.jpg

 

IMG_3087Small.jpg

 

IMG_3084Small.jpg

 

Or this setup which uses the light vacuum at open throttle. It tees the upper and lower breathers together and plugs into the top of the air cleaner.

 

IMG_2657Small.jpg

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I think you guys are  making this harder than it is.

 

I myself route the valve cover hose down under neath car

 

crank case  open vent and have done so for 12 years on my Banzai car.40mm mikunis. yes its stinky.

yellow 510 with 44s has been  open vent since 1984 at least also and  still running.

I don change the oil that often on these either. Be honest ost datsun will break for other reasons than these PCV issues of oil going bad. More liketly to run out of oil from being lazy to check it.

Not running one right away isnt going to kill this car.

 

Silkys Johnson and Stoffregen Motorsports  look reaaly good set up and As datzenmike suggest route a hose inside of the filter is another way to suck up the stink.

 

If anybody has a opne crank vent just ck it at idle and fedeel the air blow out then rev it up youll notice it will suck in.

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Great info, guys.  The setup that Stoffregen is using is pretty much what I had in mind.

 

However, I don't want it venting near the cowl and potentially stinking up the interior - Plus, I don't have a cool can like that one.  :)

 

I'm really leaning towards simply running a hose from the valve cover port and the crankcase port, into a T, then extending a single line down next to the transmission with a breather on the end.

 

Is there any reason I can't / shouldn't do it this way?

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Great info, guys.  The setup that Stoffregen is using is pretty much what I had in mind.

 

However, I don't want it venting near the cowl and potentially stinking up the interior - Plus, I don't have a cool can like that one.   :)

 

I'm really leaning towards simply running a hose from the valve cover port and the crankcase port, into a T, then extending a single line down next to the transmission with a breather on the end.

 

Is there any reason I can't / shouldn't do it this way?

 

That will work but you don't have the benefit of the PCV system. It's worth the effort.

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