Topic: PCV & Vacuum Connections
in Forum: C3 Engines
Lifetime MemberAfter reading the threads from RHeyboer's "Engine Trouble" I'm thinking my vacuum and PCV is not connected right on my 427. I have 2 PCVs one in each rocker cover and they are connected directly to the intake manifold. After reading what Ken and Ben wrote I should have only one and a (breather?) in the other. Not sure what a breather is unless it is a oil cap that has that wire mesh in the top half. I'm assuming I also should have the PCV connected to the Carb instead of the intake? One rocker cover has 2 holes today there is the oil cap in one and a PCV in the other. Any suggestions on what I should do to connect this right would be appreciated.
Lifetime MemberModerator
You need some kind of breather on the other valve cover. It can be a filler cap with the mesh like you described, or,(as it should be) a tube from the v. cover to the air cleaner, with a small, fiber filter inside the air cleaner base.
The PCV "sucks" the normal engine blow-by out of the crankcase, and into the intake, to be burned during combustion. In order for the PCV to do this, it has to have an open inlet source. This is where the breather comes into play. It allows the PCV to draw in clean, filtered air through the engine. Think of it like this.
The engine needs air, and it sucks that air thru the carb. If you seal off that air supply, the engine can't get any air, and it will not work. The PCV system works the same way. It needs an air supply(in) to work.
If you only have one v.cover with two holes in it, and the other v. cover has NO holes in it, you need another hole! You can put a breather cap where the oil-fill cap is, but the system will work much better if it draws the PCV air from the opposite side of the PCV valve. Otherwise, the only thing it is going to "ventilate" is the one v. cover.
Now....someone else can put all this in a much easier to understand terms!!
Joel Adams
C3VR Lifetime Member #56 
My Link 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
light on an aspect of our cars that I'd sort of half-understood, but not
nearly as clearly and concisely as you've just laid out.
In replacing various bits and pieces so far, I could see some of the basic
layout of the system you described, but I didn't really grasp how it all
worked, or why the parts were set up the way they are. I'm still puzzling
my way through all the array of hoses and other assorted items in the
engine compartment (not to mention the rest of the car!), and every time I
read one of your simple-enough-even-for-me-to-understand posts, I
come away feeling like I'm one valuable step closer to being able to do
more on the car, and thus enjoy it all the more.
So thanks for taking the time and effort to share your knowledge, and for
being such a great teacher.
Lifetime MemberI think I have it. One cover has 2 holes and the other one has one. I can replace the oil cap with a breather type and just reroute my PCV on the other cover to the base of the carb. Plug the second hole in the cover and plug the intake and I should be all set. Thanks for the info.
Is there any place one can go to find out exactly what type or a part# PCV you should be using? I have 2 but no idea if they are correct. Someone mentioned you need to also make sure you have the correct ones or that will also cause issues.
Lifetime MemberI think I have it. One cover has 2 holes and the other one has one. I can replace the oil cap with a breather type and just reroute my PCV on the other cover to the base of the carb. Plug the second hole in the cover and plug the intake and I should be all set. Thanks for the info.
Is there any place one can go to find out exactly what type or a part# PCV you should be using? I have 2 but no idea if they are correct. Someone mentioned you need to also make sure you have the correct ones or that will also cause issues.
[/QUOTE]
Remember this should be 1 in 1 out..
two breathers does nothing
two pcv creates a vaccum in the crankcase
one pcv and one breather is correct
the "in" is the breather cap (or connection to main breather).. the "out" is the pcv to carb
it doesnt matter which side you put them on... as long as they are on opposite sides and opposite ends.
ie.. if you have the PCV on the drivers front... have the breather on passenger rear..
i like to compare this system to an attic fan.. if you dont open a window it does nothing... and to get full effect... open a windows as far away from the fan as possible in the house.
Lifetime MemberGot the principle down now. I can't put the breather cap in the front and the PCV in the rear because the filler cap is located at the front on the driver side and the PCV is located at the front on the passenger side. I will plug the rear hole on the driver side where the second PCV is connected today.
Thanks for all the information and help on this item.