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Senior Charter Member
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Discussion Starter #1
Folks, my vintage valve covers only have one hole in one cover. If I remember engine 101, don't I need one in each? One to take the PC valev to the carb, and the other cover needs a vented cap to allow air in??? Dang I'm easily confused now adays:) Thanks!

PS. Mota is stock 302 with Edlebrock manifold and carb.
 

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Senior Charter Member
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573 Posts
Kobrak,
Let me tag onto to your post and join you in 'engine 101. 427FE with rear intake manifold breather and front intake manifold fill (no valve cover breathers). Any way to vent fumes into the engine short of drilling the covers? Thanks for the tag along.
RB
 

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Senior Member
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3,760 Posts
Hello Kobrak, howya doin? That fuel tank cover you sent me for FREE is all installed and lookin' good with a fresh coat of satin black Plastikote, thanks again.

No breather cap is needed or even wanted with a PCV valve on a carbed engine. The internal pressure that forces oily air through the PCV and back (eventually) into the air/fuel mixture is caused by a buildup of blow-by at the rings. Even perfectly gapped piston rings allow some blow-by, there needs to be a way to vent that pressure. PCV valves replaced the messy old breather caps.

But you do need a second hole to put in an oil filler cap. It's either than or pull a valve cover every time you wanna add oil! :eek:

AJ
 

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Here's the way I see this issue....

1) Under each rocker cover are holes where the push rods go down into the cam shaft valley. As a result, any pressure build-up cause by piston ring 'blow-by' will be equal in both heads.

2) Just one vent with PCV valve connected to the carb will successfully vent both banks of cylinders because if #1.

3) The comment about adding oil, although true, does not affect the breathing since that particular orrafice is sealed when closed.

Does this describe things accurately?
 

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I'm running a pcv on the pass. side rear, and an oil cap with venting on the driver side. It seems to work great for me having both sides vented.
 

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Premium Member
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Kobrak,On my engine the pcv is on the back, in the middle of the intake. My car is EFI but I'm sure you only need one on one cover or the other.

Dan
 

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FFCobra Craftsman
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1,359 Posts
Guys - let me ask another way. In light of what everyone has said. Don't you really just need a vented/filtered oil filler cap in one valve cover and no PCV at all? Of do you need the vacuum provided by the PCV? What about fuel injected engines - anything different?
 

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Non-whiner
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10,646 Posts
What's going out, has got to come in. I always run a pcv in one cover and breather in the other. Most auto repair manuals have a diagram showing the path through the pcv and breather. Most EFI have the valve in the manifold.
 

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Mark L, you are correct, but for one it's not as environmentally friendly, two does not do as good a job as a pcv, and three can be a little messy on your valve cover.
 

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Discussion Starter #10
I was planning on running the PVC to the carb front. That was it. I was talking to Summit Tech line and they said you should always be running a PVC and a return. I was sitting there going what the heck? I got one hole!!! LOL. The thing I worry about since this conversation this morning is the fact the motor has a lot tighter tolerance than the old stuff I used to work on. I'm wondering if this is cause for concern on proper engine ventation? Think I'll just look into a different set of covers:)
 

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2savage,

Good point on #1. I never realized that but you're 100% correct about those head passages. On my Edelbrock heads, there is also an ovel shaped oil/air orifice between Cyl #1 and #2, #3 and #4, #5 and #6, #7 and #8 at the top of the head next to the lower intake.

So should the valve cover on the opposite side of the PVC cover need a breather to ambient?
 

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FFCobra Craftsman
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1,626 Posts
It wasn't a ford, but I ran a PCV only setup, no breather, and the vacum buildup in the block was so great that air was sucked through the rear seal creating a noise that sounded for all the world like a bearing that was screaming. A PCV valve needs a breather as well, but it can be a breather/PCV combo.
 
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