# ‘65 GTO w/ ‘69 RAIII Heads - PCV ventilation



## Roqetman (Aug 31, 2015)

My ‘65 has the original 389, bored 30 over with RAIII heads. I found out the hard way that stock 389 valve covers are not tall enough to clear the valve train so I installed 400 valve covers. I’ve noticed many 400s have a plug on one valve cover and oil filler on the other side. My current set up is a screw-in oil filler cap (non-vented) on the driver side and an air breather cap on the passenger side. The PCV valve is located in the valley pan in front of distributor and is routed to the PCV vacuum port on the Q-Jet. My question has to do what ventilation is needed for proper PCV operation. Is the air breather cap needed or can it be plugged with a rubber cap? My thought is this, if the carb is pulling in crankcase gases from the PCV is there any need to have an air breather on the valve cover. Thanks for helpful advice! See pics for clarification.


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## PontiacJim (Dec 29, 2012)

Roqetman said:


> My ‘65 has the original 389, bored 30 over with RAIII heads. I found out the hard way that stock 389 valve covers are not tall enough to clear the valve train so I installed 400 valve covers. I’ve noticed many 400s have a plug on one valve cover and oil filler on the other side. My current set up is a screw-in oil filler cap (non-vented) on the driver side and an air breather cap on the passenger side. The PCV valve is located in the valley pan in front of distributor and is routed to the PCV vacuum port on the Q-Jet. My question has to do what ventilation is needed for proper PCV operation. Is the air breather cap needed or can it be plugged with a rubber cap? My thought is this, if the carb is pulling in crankcase gases from the PCV is there any need to have an air breather on the valve cover. Thanks for helpful advice! See pics for clarification.
> View attachment 134656


Gotta have a breather to let air in. If you didn't, a) you would have created a vacuum only and no air flow, b) at high RPM's you will build enough internal pressure as the pistons go up and down and pump internally and blow out your gaskets.

Its your call if you want to plug up the hole.


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## Roqetman (Aug 31, 2015)

Thanks for the clarification. I don’t want to blow out gaskets!


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## Lemans guy (Oct 14, 2014)

You have an air breather cap on the passenger side and A PCV in the valley pan routed to intake. Yes PJ is right, do not plug your breather. Actually two breathers can be used as well and better breathers. Those chrome ones look nice, but the K&N type valve cover breathers have much more filters area to let your crankcase breath.

your crankcase is like your lungs, the bad stuff goes out, blowby gases condensation, crud, contaminated oil etc...by the intake vac sucking it out thru vacumn.....

but your crankcase and your intake are not the same, they are two distinct chambers so yes the crankcase needs fresh air. Your PCV needs operational efficiency.

plugging your valve cover breather would be akin to injecting your lungs with a virus, and the result would be hard to breath, and then you spit up oil out the breathers and gaskets etc. Go to Me Wagner site and read watch there info. A system like thatyou can feel your engines improvement.....


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## Roqetman (Aug 31, 2015)

Lemans guy said:


> You have an air breather cap on the passenger side and A PCV in the valley pan routed to intake. Yes PJ is right, do not plug your breather. Actually two breathers can be used as well and better breathers. Those chrome ones look nice, but the K&N type valve cover breathers have much more filters area to let your crankcase breath.
> 
> your crankcase is like your lungs, the bad stuff goes out, blowby gases condensation, crud, contaminated oil etc...by the intake vac sucking it out thru vacumn.....
> 
> ...


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## Roqetman (Aug 31, 2015)

Thanks for the info!


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