The GM system described earlier - and the Ford versions of the later era - used clean ventilation intake air pulled through the carburetor air cleaner by the PCV valve. Because the amount of air you would use to PCV ventilate can easily be overpowered by blowby of an older engine - the described intake system allows reverse flow back toward the carburetor. On our older systems this "overflow" would be pushed back out the oil filler tube.

This older picture of the Greenbird shows a "homemade" fitting used with a '64 292 PCV fitted (in the proper check valve direction) with hoses grommets and clamps. It also had to be fitted with an orifice, as its original installation was into a port of the manifold that incorporated small holes into both chambers of the "cross H" manifold.


 
 Steve Metzger       Tucson, Arizona

Here is a quick video of my PCV setup.



https://www.youtube.com/watch?v=fqgyyF16Go8



I connected two old draft tube "housings" together and put a grommet into one, the grommet holds the PCV valve and that in turn connects to the vacuum port in front of the carb. It's in line with the vacuum wipers, so I have a check valve to keep anything from entering the vacuum wiper pump. The engine draws fresh air in from the oil fill tube.

Almost all the GM stuff did the same thing as Drylakes posted. And it did work. Filtered air is a must, you wouldn't really want to dump dirt in the crankcase.

Frank/Rebop

Bristol, In ( by Elkhart) 

I hate to point this out but if you will notice a million of "C" brand GM engines their PCV valve was pushed into a rubber gromment in one rocker cover going to a place under the carband the opposite rocker cover had a hose that went to the side of the air filter with a small "brillo" looking filter mounted inside. Others had the hose entering between the carb air filter and the carb. When this all happened the oil filler tube disappeared and an additional sealing twist cap went on the rocker cover for that purpose.

Silly as it may seem filtered air is a must to keep things in working order. How many of you have noticed the automatic choke air tube that goes under the intake manifold enteres in the side of the teapot carb used filtered air? When I change to a Carter WCBB or a Rochester 4GC I make sure the new tube goes into tha carb air filter adapter plate to continue this practice...JD

56 Vic, B'Ville 200 MPH Club Member, So Cal.

The PCV valve location and the air inlet to the crankcase for the PCV valve supply air needs to be separated. If the crankcase air inlet is going to be the original oil fill tube at the front of the valley cover, then putting the PCV valve at the rear of the valley cover is the logical and simple location for most Y's. Here’s a past link touching on the air flow path for a PCV valve.

http://forums.y-blocksforever.com/FindPost25383.aspx

Performing an advanced search on this site using ‘PCV valve’ and selecting ‘all terms’ will bring up more.

Lorena, Texas (South of Waco)

Fair enough, thanks for the responses.

Now would a pcv valve correctly placed in the valley pan down draft tube location be superior, or would this set up work better coming off the valve cover? I ask because i have both a modern down draft tube adapter, a down draft tube, and a hole in one of my valve covers. I could even y a combo of both if called for. I plan on making my 61 unibody truck my daily driver, and would like it to run as clean as possible crank wise.

Charlie..I agree you need a lot of exhaust flow to make that style of pan-a-vac system work. That why it was only used in racing and the tube welded in the exhaust header had to be done correctly. The belt driven vacuum pump system worked all the way thru the RPM range. There are still skeptics on it's use but I'm not one of them....JD

56 Vic, B'Ville 200 MPH Club Member, So Cal.

What I understand is that the race system does not function at low (street) engine speeds. So it will do nothing for you.


Lawrenceville, GA

Unibody...What you describe is a drag racing idea to evacuate the engine to run in a vacuum for "free". You see it used a lot where racers do not want to install a true vacuum pump costing the extra HP. You need to install a A.I.R. oneway valve in the system to prevent exhaust gases from entering the engine. I had one on for years prior to the pump. I have never heard of anyone using one on a street engine.

A PVC system is for emissions which actually helps your engine compartment clean and can help with engine leaks also. I installed aftermarket ones in the 60's in when California mandated them. No matter the car brand an AC unit worked the best. We ruined a lot of valve covers and air cleaners with putting holes in them. You always needed to turn out the idle mixture screws sometimes a lot depending on the condition of the engine.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Sorry in advance for the newbie questions. It was suggested to me that the draft tube could be vented via a bung, welded into my exhaust pipe, near the manifold, since it was a pre smog vehicle.

This would help with the vacuum. Is this viable? would the exhaust gases be hot enough to burn off the vapors? Legal? If so would using the pcv be advised?

John