[quote]569104 (2/15/2011)

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Ok,



Please help me understand. If I block off the draft tube and run a pcv from back of valley cover and have a standard oil filler cap then wouldn't I just be pulling fresh "unfiltered" air through the cap and under valley pan into pcv and not venting the crankcase at all?



I have a "filter" in the draft tube that is equivelant to the wire mesh common in the oil filler caps. I also have vents in the valve covers. It seems to me it would be better to pull the fresh air through the crankcase and valve covers and out the oil filler tube into the engine. Seems like this would provide better "crankcase ventilation" to me. What I'm not getting? Thanks for the help. (quote)



The original oil cap had an oiled wire mesh filter (good for keeping out pebbles and large bugs), the repro caps have a foam filter (I clean & oil mine frequently for increased filtration), but the best would likely be an oiled cotton K&N type that seals tightly to the filler pipe. I DID try one of those but found that it was too tight a seal. Cotton filter would get saturated with oil pumped up by high RPM crankcase pressure, and drip on the engine. Better to let some oil mist escape around the looser fit, unless a system could be rigged to drain the oil back.



I initially also assumed that a lower fresh air intake would be more logical, but I guess when the cool air enters the fill pipe, it fall down to replace the hot blowby gasses being sucked out from the rear of the valley.

6 VOLTS/POS. GRD. NW INDIANA

You can rig a test to see if there is any vacuum in the air filter housing. Fit a nipple to the housing, attach a vacuum gauge, and run the engine. Because it's such a large volume, I doubt it will produce enough vacuum, if any at all to provide the desired effect. It shouldn't be any worse than a typical breather system.


Lawrenceville, GA

You make a valid point regarding vacuum signal.  What I was thinking of is a PCV with a very light spring (or maybe even simply an open line with a wire mesh filter) such that all but idle velocity would help vacate the "gases" in the valley and recirculate them in the combustion cycle.

This shouldnt create a "vacuum leak" senario as might a light spring PCV plumbed directly to the carb circuit or intake manifold. There should still be negative flow throught the oil filler cap, there should be less fumes into the air/garage, and with a PCV or mesh filter inline, it should minimize the heavy partical contaminants being re-introduced to the venturis.

Am I really way off track in my thinking?

Cheers... Brian

Cylinder Index = 84

Current Experiment = `57 Tbird, Grand Rapids, Michigan

Do you park your truck in the garage?Do you notice the smell of oil and fumes when you open the door after its been kept closed overnite?When you close off the draft tube it seals the block and you wont get that smell anymore.One more reason to use a PCV system.

  

Thanks Ted,

So what your saying is the way I have my engine set up is OK and would actually provide better evacuation of crank case "contaminants"?

   

1956 F100 Big Window 309ci Y-block,  1956 F100 small window 272ci Y-block

Greg.  Mountains of North Eastern CA

The cap itself is filtered with mesh which filters the incoming air.  The later model PCV systems went the extra step and ran a hose from the cap to the air cleaner to insure pure filtered air but tends to be overkill for a simple PCV valve retrofit.  The intent of bring fresh air in from the opposite side of the engine from where the PCV valve is located is to set up an air flow that will pick up moisture and other contaminants from the valley area of the engine.  Having the fresh air inlet and the PCV valve close together minimizes the amount of contaminants that can be pulled from the engine.  I believe that answers what you are asking?

Lorena, Texas (South of Waco)

Greg, it isnt a hi jack, but even if it is so what.  I have done a few myself .

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Ok,

Please help me understand.  If I block off the draft tube and run a pcv from back of valley cover and have a standard oil filler cap then wouldn't I just be pulling fresh "unfiltered" air through the cap and under valley pan into pcv and not venting the crankcase at all? 

I have a "filter" in the draft tube that is equivelant to the wire mesh common in the oil filler caps.  I also have vents in the valve covers.  It seems to me it would be better to pull the fresh air through the crankcase and valve covers and out the oil filler tube into the engine.  Seems like this would provide better "crankcase ventilation" to me.  What I'm not getting?  Thanks for the help. 

Mike I don't mean to hijack your thread.

   

1956 F100 Big Window 309ci Y-block,  1956 F100 small window 272ci Y-block

Greg.  Mountains of North Eastern CA

Aside from all that dirty/unfiltered air contaminating the oil, when the system goes positive-pressure at high RPMs, the crankcase opening will likely pump out more oil, as the agitated lube (compared to the valley/valvecover space) is probably creating a heavy mist? Also, what might be the deleterious effects (if any) of the extra volume (vacuum driven) of cold fresh air injected into the lower crankcase?

6 VOLTS/POS. GRD. NW INDIANA

If you are using a PCV system you need to take the draft tube off and plug the opening with a cup type plug.Having the draft tube AND PCV defeats the purpose of the closed engine crankcase ventilation system.Fresh air is supposed to be drawn in from the oil filler cap.If you leave the draft tube on fresh UNFILTERED  air is drawn IN from that source instead of the cap so you dont really get a fully ventilated engine.