The conventional thinking is that PCVs keep the engines cleaner.  But what about drawbacks of the addition of relatively contaminated and heated air into the A/F mixture?  Looking at all the components of a used PCV system usually shows heavy carbon deposits.  I had one late model 2V metal PCV tube almost completely closed from gunk.  Quite a few other OEM aluminum spacers with PCV connection also have been found heavy with carbon like deposit, meaning whatever isnt deposited goes into the cylinders.

The late model 2V manifolds have the gases routed to and from the PCV going only to the front 4 cylinders.  It seems like the front 4 would be lean or the other four rich.  Curious, at least to me.

Is there a tried and true inline PCV that can go between the late model valley with rear cap, and the carb/spacer?  The PCV I am currently using mounts into a bushing at the valley rear.  It produced the same effect as a vacuum leak, with hoses going to each side of an aluminum spacer.  Ended up having to decrease diameter of openings at the spacer to about .180 inches.

I have heard that a PCV has a greater tendency to produce oil leaks from the engine generally, compared to a draft tube.  True False?   

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.

Since I installed one it stopped leaking all together.I am happy with the way it runs.I ended up using one for a 300 six.The one for 302 seemed like it had a vacuum leak.My engine used to leak from every place that it could except the rear main.

55 fairlane gasser 312 /c4, 57 f100 292/c4, 52 mainline gasser 302/t10 4speed

Mike, I also have removed the draft tube, and have the valley pan that is vented at the rear....and have a PCV valve between it and a port on my Demon carb, connected by short lengths of heater hose. At least this setup spreads the gases fairly equally to all 8 cylinders. I too was a little concerned about the amount of air passed into the A/F mix via the PCV arrangement. I read (probably on here) that about 3 cfm go through it under normal conditions. Trying to limit this, I switched to a AC Delco PCV valve that's actually intended for a 231 ci GM. It runs fine. I took things apart recently to check it out and everything's OK, although it's only been a coupla hundred miles. I plan on checking it regularly, as it is somewhat of a restriction.

On my previous build of the engine, I used a PCV valve from some GM 305 V8 application. It had a nipple on each end. One end was the same size as the hose nipple dealamajig that bolts to the valley pan and the other was the same size as the port on the carb. I don't remember the application. I found it by looking at the pictures of various valves on advanceautoparts.com or napaonline.com. While I do still have the valve... somewhere... I have no idea where I've put it to see if it has a number on it.



Road draft or pcv, they will all clog, given enough neglect.


Lawrenceville, GA

The vacuum leak which was produced by my PCV really surprised me.  The PCV is for some engine around 300 cu in.  It has one outlet with an adapter on top that will take a 5/16 hose and a 3/8 hose.  The hoses then run to the 1 in. alum. spacer which has been taped for nipple fittings.  So, the PCV gas enters the spacer primary bores immediately below the throttle blades, at a right angle.  Maybe there is a venturi effect at the entry of the PCV gas which caused more flow than usual.  I filled the inside of the brass barbs with lead and then drilled it out to create more restriction.  Seems to work ok.  I dont actually remember what the final size is inside the barbs.

The PCV Charlie had in his earlier engine is what I have in mind.

Hadnt thought of using a PCV for a much smaller engine (duh).  Perhaps that plus a draft tube would be a possibility, if I get one of the earlier blocks with a side mount together. 

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.

This is an obvious question.Is the valve installed in the correct direction?At idle with high vacuum the valve should close(or almost) working against a light spring pressure inside the valve.This should do away with the "vacuum leak" at idle.As vacuum drops off idle the valve opens to draw more air from crankcase.On mine I started with a valve from a 302 which was too big and went to a smaller valve from a 4 cylinder Fairmont or Zephyr.Worked much better. The PCV system was created to help air quality.Instead of oil and gas fumes dumping raw out the draft tube they were reburned using the PCV valve.As far as oil leaks this system should reduce internal pressure as the "positive" in PCV states.The open draft tube system is a passive system as far as air in and out.If you are tapped into the spacer plate that is the correct hookup point if not availalble at the carb itself as done with my Holley 390.There is a tube to hook the line onto.Some people have used the vacuum fitting at the back of the intake to draw fumes which will give lean mixture in the rear cylinders.You could also tap the intake under the carb as long as its central to the motor.

  

When I first installed a PCV kit (CASCO blue FoMoCo valve, and rear-ported alum. carb spacer), I was running max. ignition advance (Loadomatic). The leaner charge caused an alarming ping on acceleration. Instead of retarding, I cured the ping initially by inserting a restrictor into the PCV hose to the valve in the valley pan. Tinkering with the distributor has since allowed removing the restrictor, and the car runs fine today.

Suppressing leaks, eliminating noxious fumes/oil mist that contaminate the engine are a PCV's main advantages. Of course though, any motor fed a charge diluted with blow-by & oil will not produce the same power as one burning pure gasoline of the right A/F mixure.

6 VOLTS/POS. GRD. NW INDIANA

I once saw a mechanic plug the PCV for an old Pinto 4 banger. As soon as he did the smoke started pouring out of the tail pipe. Rings were bad. That says to me that the PCV relieves a lot of crankcase pressure.

From what I'm reading here which PCV makes a difference. Is there one that is specificaly recommended for the Y-Block? Seems they all have different flow rates. I used a screw in type from a later FE. Still get some puff from the oil filler at times. Chuck in NH

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

The engine in my driver is a stock 292(except for .080 overbore) and the factory PCV from a 64 truck engine was too big.I had to put a restrictor in the line to keep it from leaning the engine way out.

 

Paul,

Boonville,MO

Interesting about the `64 truck PCV being too much cfm and it vac leak effect... I'm gonna plum a `64 truck set-up to the bottom of the air filter base... will afix a wad of steel wool (the stuff from a typical oil filler cap/breather) at the port openning inside the filter base and then occassionally check for contaminate build up... shouldnt be an issue on healthy motor, right?

Cheers... Brian

Cylinder Index = 84

Current Experiment = `57 Tbird, Grand Rapids, Michigan