I hate food fights (well, not really) but there seems to be a little confusion on this subject.

Just because one has never seen a crankcase explosion does not mean they do not occur. The valve is also a safety device for the system in that it shuts off the crankcase from the intake manifold in case of an intake manifold backfire.

The PCV valve will also protect the engine in case of a backfire, which causes a sudden high-pressure pulse in the intake manifold. This forces the PCV valve closed so that the backfire flame can’t reach the crankcase, where it could ignite flammable fumes and cause damage.

SOURCE- http://dannysengineportal.com/pcv-positive-crankcase-ventilation-valve-faq/

____________________________

Just saw this old thread today.
Whether there is/was any confrontation doesn't matter to me at all.
I learned a lot & appreciate the education.
I'd like to know what one does for  PCV on a modified engine with low vacuum?
How's that accomplished? Maybe I'll start a new thread.
Jim

Welcome to the site.
PCV valves do need to be as high up in the engine as possible to take advantage of heat rising which helps in removing cold start moisture residuals and other contaminants.  Attempting to hook up the PCV valve at the lower block road draft tube opening never has good results simply due to too much oil spraying around in that area and that oil getting picked up in the lower mounted PCV valve and sucked back into the cylinders.  Valve covers and the valley cover are the accepted locations for a PCV valve.
 
Here are links to a couple of past threads giving some more details on PCV valves.
Crankcase evacuation
Why a PCV valve or system? 

Lorena, Texas (South of Waco)

Aloha!
My 312 has the road-vent tube w/ canister on the lower left (drivers side) of the block.  There is no hole up on top rear of the block by the distributor.  Anybody know of some adapter kit or recommended way to simply utilize the existing road tube or that location for PCV.  I do have a 4BBL mounted carb spacer already with a blocked tube I can use to pull fumes in.  
Mahalo!

Amen Cereal Killer. After 40+ years as a mechanic in Ford dealers, I have never seen a crankcase explosion and have only heard secondhand stories about them. If your car is running so bad it might have a crankcase explosion, you have more problems than a wrong PCV valve.

Dan      Kingman Az.      86409

sorry guys like cereal killer i cant stand it any longer

any guy that can get his car out of a shed after winter put it on a truck & without raising the hood can pull 11sec runs on a drag strip knows what he's doing, i believe the original thread of dutchys was a simple re-post of his old thread which seems to have got highjacked .

btw dave as you have only been with us a short time the reason your specified thread from mr4sppedford didnt get told about picture posting is john may have broadband so he woudnt have trouble loading it & as ted hasnt said anything its possible being as busy as he is may not have seen that post yet & both are the moderators for the whole site as jim the owner cant keep an eye on everything while he works in the back ground so we can all benefit from y-blocks forever. thats all im going  to say.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

ENOUGH SAID!!!    And God Bless You All    Eddie

Eddie

Lake Forest, Ca. 92630

  Here is a picture of the Ford PCV valve from a 68 Mustang/Cougar manual. If you look close you will follow the operation of it.

When engine is at idle with high vacuum the jiggle pin moves toward the right when vacuum has overcome the spring and closes down the flow past the jiggle pin where marked "to intake manifold" on top picture, you will notice the spring is more collapsed in this condition and the rear of the jiggle pin is more open.

When engine is in high speed operation/low vacuum the jiggle pin is more toward the left with a greater opening on the "to intake manifold end", however the "from crankcase end" is more closed and restricting the flow caused by the spring. Notice the flat end on the jiggle pin by the dual arrow at the "from crankcase or rocker cover" end. Air flow does not pass through the jiggle pin. It passes around it as the jiggle pin is a solid piece with no through hole.

If in a backfire or blowback condition the jiggle pin will more toward the left (ie) pressure has come from "to the intake manifold" end forcing the jiggle pin towards the left and closing off the orifice hole to the "from crankcase or rocker cover" end by the flat end of the jiggle pin.

marv

John, I believe that you are correct, nonetheless we don't need this kind of confrontation on this site and I congratulate you on your restraint..  Keep up the good work with your vehicles and good luck with the "Hurricane"'  Thanks for all your help on this site. 

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

Dave:

I did not refuse to quote because I would be proven wrong.  I'll go ahead and quote, but you still have the option of telling me again that I can't read, or that I changed the wording.  Here goes, 1968 Ford/ Mercury manual, section 8-33, under the heading "CLOSED CRANKCASE VENTILATION SYSTEM": The first part of the explanation tells how the air gets into the crankcase and how it circulates within it.  Do you want that quoted too?  Then it continues:  "During idle, intake manifold vacuum is high.  The high vacuum overcomes the spring pressure and moves the valve to the low speed operation position (Fig. 10).  With the valve in this low-flow position he ventilating air passes between the valve (jiggle pin) and the outlet port.  In this position there is minimum ventilation but it never completely seals off the air flow.

     As engine speed increases and manifold vacuum decreases, the valve spring forces the valve to the full open position (Fig 10).  This increases the flow of ventilating air."  End of explanation.  Next words on the page are the heading for the next section, "EXHAUST EMISSION CONTROL SYSTEMS".  I would go ahead and quote the GM manual, but if I can read it correctly, it says essentially the same thing.  So does the Chilton.  I quoted the Ford manual for your benefit, Ford man that you are.

Now to my fellow Y Blockers on this site.  I apologize for extending this thread to this extent, and I will have nothing further to add.  Thank you for bearing with me.

John - "The Hoosier Hurricane"