Well that's different.....

So while I wait for my baffles to arrive I've been contemplating other contributing factors. For those of us heathens, with Holley carbs - how have you set up your PCV system?

I have a four barrel.
I have a Wagner adjustable PCV valve in the LH cover over a P6 baffle. The pipe goes from this to an oil separator mounted high up in front of the heater. A pipe goes from the separator to the intake spacer plate behind the carb.
The RH rocker cover has an open to atmosphere breather cap over a P6 baffle.
The rear block breather has a pipe on it that goes to an underside stub on the aircleaner base.
As previously said the engine used to suck in oil without the separator fitted.
 
When I had a four barrel, I connected the PCV port on the weber (Straight to engine vacuum) with a pipe to a PCV valve on the N/S rocker cover. This created a negative vacuum in the crankcase, so air had to get into the engine.

I then just used a small filter on the O/S rocker cover so that any air drawn into the engine was filtered.

Don't try this without a PCV valve :oops: it's there to control the amount of vacuum, the higher the suction, the lower the amount of fumes allowed through.

PCV weber.JPG
 
The Leyland 4.4 Rocker covers have a PCV port from factory - a fellow P6 fan is sending me a set once he's done fighting bushfires. One thing I noticed however is that on the 4.4 one cover has the PCV and the other has no breather at all. Where do the 4.4's draw air from to vent? Does the oil cap vent?


I guess in the meantime I might 'adapt' the P6 covers to take a PCV. Would dual catch-cans (one on the PCV side one on the 'open' side) be overkill?
 
Last edited:
It depends a bit on which 4.4 you are looking at. The truck engines came with pipe in the sump which goes to a vacuum pump. The car engines are like the 3.9 and there is no air inlet.
 
I believe it's out of a Leyland P76 (currently in a Landrover). How does the PCV work with no inlet??
 
Last edited:
The Leyland 4.4 Rocker covers have a PCV port from factory - a fellow P6 fan is sending me a set once he's done fighting bushfires. One thing I noticed however is that on the 4.4 one cover has the PCV and the other has no breather at all. Where do the 4.4's draw air from to vent? Does the oil cap vent?


I guess in the meantime I might 'adapt' the P6 covers to take a PCV. Would dual catch-cans (one on the PCV side one on the 'open' side) be overkill?
You only need a catch can on the side going to the intake. The open side will be drawing air in, if the system is configured correctly.
 
Cheers - I thought that under certain driving conditions the flow reversed. It's late at night here so I might be getting confused.
 
I believe it's out of a Leyland P76 (currently in a Landrover). How does the PCV work with no inlet??
To my mind Positive Crankcase Ventilation is extracting blow by gasses by sucking them out of the crank case via a vacuum acting on a valve linked to the intake.
This system relies on air being able to enter the crankcase, if no air can enter how can gasses be extracted ?
In order to manage the system effectively the PCV valve has to be tailored to the vacuum of the particular engine, so plopping on a generic valve may not be ideal. When fitting a valve the fuel / air mixture will need re setting as you are leaning out the mixture by adding more air into the intake.
 
Cheers - I thought that under certain driving conditions the flow reversed. It's late at night here so I might be getting confused.
The flow will always remain as a pull from the intake, but different driving conditions mean the flow varies, this is controlled by the spring loaded toggle in the valve, Which is why a valve from a big block Chevy will have different parameters to a valve from a 2L Pinto.
 
I'm going to use a widely available PCV from the old Holdens. Both the 3.3 6cyl and 4.2 8 cyl 70's Holdens use the same PCV, so it should be ok for the 3.5......?
An adjustable one like you have would be best, but the budget is tight.
 
Cheers - I thought that under certain driving conditions the flow reversed. It's late at night here so I might be getting confused.

At full WOT there will be very little vacuum to pull gasses out, and if your engine is not in absolute tip top condition, there may be more blow past than the vacuum can handle so it is possible to get the gasses leaving the crankcase through the inlet - (the little red filter in my picture)
 
At full WOT there will be very little vacuum to pull gasses out, and if your engine is not in absolute tip top condition, there may be more blow past than the vacuum can handle so it is possible to get the gasses leaving the crankcase through the inlet - (the little red filter in my picture)
I would accept that.
Bear in mind, how long does a street car spend at WOT versus time spent at all other throttle settings ?
 
Here's my theory... If your 4.4 is carburetted, set it up like mine where all blow past goes into the air filter before the carb. All bad gasses will get re-burnt and no pressure on the inside of your engine to push oil through seals etc (don't forget the lovely flame traps). If it's injected and you don't want to go through the remapping, rolling road tuning, finding the correct PCV etc, get it back to the factory set up exactly. I be-leave modern engines adjust mixtures according to the myriad of sensors but the early injection systems, I haven't got a clue. (Who wants a modern yawn mobile anyway):LOL:
 
So there are 2 different systems we are dealing with here.
PCV, Positive crankcase Ventilation. Where the carbs/injection system draw a measured amount of air from the crankcase via a PCV valve using manifold vacuum. And..
CV, Crankcase ventilation. Where the natural blow past of the combustion process positively pressurises the crank case where this pressure is allowed to escape via a controlled environment (back through the engine's combustion chambers) or out to the atmosphere (preferably via a catch can and filter).
The way I see it in your case, With only one PCV attachment, disable the valve so air will move through it freely and feed this either directly into the carburettor side of the air filter. This way all nasties get burnt through the engine and the vented air becomes part of the ordinary combustion mixture. If you are blowing a lot of oil out the breather, feed it via a catch can then into the carburettor side of the air filter. Don't feed the breather on the intake manifold side of the carb. This will upset the mixture severely. Had something similar but different :rolleyes: with a warped valve cover on the brake booster (the white round thing) where it was letting in air causing the cylinders nearest to where the vacuum hose entered the manifold to run very lean. (this is never good).
PCV's are used in a designed system. They can't just be put in willy nilly because they look good. (as CB has already mentioned:thumb:)
I suggest you have a talk to an engine tuning specialist if in doubt with your car at hand.
Getting an engine bay looking right is not always easy but very rewarding. ;)
 
Cheers - the installation is purely functional - but I want it to look neat. The engine has been converted to a Holley so I'm basing the PCV system off the old Holden engines I used to have of a similar capacity. I started looking into this as I was getting a lot of oil in the air filter with just a Cv system as had been suggested to me when I converted to down-draught.
 
Rocker bolts re-torqued, baffles installed, cut a hole in my rocker covers to fit a new PCV and grommet, installed a 1/2" plate with a PCV port under the Holley (Holley doesn't have one). So now I have a breather on the 1st bank and PCV valve to manifold on the 2nd bank. Seems to be working so far. Hoping to take the old gal for a more spirited run soon to see what happens. Your advice on here has been invaluable, and the cause of me still having the car! Cheers guys :)

PS P76 Rocker Covers still on the way, to make it look better :)
 
Now - new job to chase down the intermittent vacuum leak whistle. I suspect the home made manifold. Time for an Edelbrock perhaps?
Oh, and I think the temp gauge is faulty. New sender unit but gauge still intermittently goes into the red - have stopped the car and engine is definitely NOT overheating....must be gauge or wire.....??
 
Last edited:
The instructions in my Wagner call for the valve to be spaced up from the baffle at least 3/8". If your PCV valve is pushed right in to the grommet then it may be too close to the baffle and still suck oil.
To raise it, place the required amount of tight fitting O rings over the valve before fitting.
 
Back
Top