My Crankcase Ventilation Question

[rarerodder]

There's many threads covering this topic and I think I have read them all. Seems there's just as many versions of how to accomplish so I just wanted to ask to be certain.

My 434 will be running a single four Edelbrock intake with vented oil filler cap and Holley 770. I riveted the baffle to the bottom of the intake which covers the 'draft tube' hole. Intake came with a grommet, connector, hose, and metal elbow to vent to bottom of air cleaner; but, no PCV. My question is can (& should I) I insert a PCV into this intake grommet, route line to base of carb and let filler cap pull air from atmosphere?

 

[La Hot Rods]

You can put the PCV in the base of the carburetor going to the grommet in the back of the intake and have the oil fill tube open.

 

[pvs409]

Like this with PVC check valve that is necessary on the back of the Edelbrock AFB carb plus this engine has the vented oil fill cap (nothing on valve covers)
The hose from the carb runs to the back of the factory 409 intake and hooks to a 90 degree tube in a grommet in the intake.
Paul

.

 

[38Chevy]

You need one of these fittings on the back of the intake manifold.
https://www.classicparts.com/mobile/1956-67-PCV-Draft-Tube-Assembly-S_B/productinfo/86-141/

 

[Skip FIx]

Edelbrock went to using that hole for the fresh air because too much oil got sucked into using it for a PCV. There is a lot of oil flying around in the valley of a running motor.The "second generation" baffle is even larger than their first design. They ,at least the dual quads,do not have a hole in the back for a draft tube type deal. I've fought oil sucking PCVs with my Pontiacs when using one in an aftermaket valley pan that does not have the baffling the stock ones do. Added a baffled grommet, a taller tube with mesh still sucked oil! Heck trying out one design it was "fogging for mosquitoes" so bad the DPS pulled me over to see what was going on!

Look at a stock SBC valve cover where the PCV is -it has a pretty substantial baffle made into it.

I used a factory repop baffle under the intake on my Edelbrock intake-it actually has bosses there to use it. I safety wired bolts instead of rivets. When I dynoed it we just had breathers but plan on using the PVC in either a valve cover or the oil filler tube.

 

[rarerodder]

Thanks, guys. That is considerably more baffle than mine has as you can see mine below. I was really hoping to put the PCV behind the carburetor to this hole in top of intake to keep things looking cleaner. Maybe if I can put a roll of steel wool or figure out some additional baffling coming out of that hole?

 

[38Chevy]

That manifold does not have the threaded hole to attach the factory pcv fitting so you will have to use a grommet that you can plug a pcv valve into

 

[Tim]

I have the same intake with a Edelbrock carb. This is how it came off the 327. They have the PVC inline to the carb. Don’t know if it’s right or not but it didn’t have any issues with oil. There’s instructions that came with the intake how to trim that plastic pipe in the grommet. If you stick it in it almost touches the shield.

 

[64ss409]

All of the suggestions above move the air from the vented oil filler cap to the rear of the engine, then through a pcv valve. Some have had oil consumption problems routing this way because of intake baffles.
Here is another possibility. Since you say they furnished plumbing to go from the rear of the intake to the air cleaner, how about moving the air the other way with a 64-65 409 oil fill tube similiar to the one below and screw on cap. Then from the fill tube 3/8 fitting to pcv valve at the carb. This would be similar to Chevy's closed pcv system. Air is drawn from the air cleaner to the back of the intake, through the engine to the oil fill tube, then pcv to rear of the carb.

 

[409gang]

My 67 Corvette 327/300hp has a oil filler tube with a twist on cap and a threaded nipple where the PCV valve screws into, kinda the same thing as above.

 

[1958 delivery]

If you connect the PCV to the oil fill tube then you run a sealed cap on the oil fill tube. The rear blow by opening would then go to the bottom of the air cleaner, air flow will be from rear to front.
If you run the pcv at the rear of the carb (vac source) then you use an open oil fill cap so air flow would then go from front to rear

There is another version of the oil fill tube that has a screw in provision for the PCV

 

[Jim Sullivan]

I tried using the valley hole in my Edelbrock intake, sucked alot of oil. I ended up drilling a hole in the side of the oil fill tube, installed a grommet from a valve cover and stuck the PC valve there. I then had to make up a baffled tube that ran between the valley hole and the bottom of the air cleaner to prevent any oil from blowing into the air cleaner.
Never did take a picture of it all welded up. I can get one if needed.

 

[heddrik]

Neat Jim, as always.

 

[Skip FIx]

Remember too if you are using a PCV the engine has to have a fresh air intake to be able to suck air in. Usually in the air cleaner so sucking clean air.

Like Jim said amazing how it can suck oil!

 

[Tim]

These are the instructions I got with the new Edelbrock 7158 intake. The second pic is what I have off the old intake. The hose from the front of the carb goes to what used to be the road draft tube that isn’t on the new intake just a vent hole. The carb has an additional outlet on the back that can be used for the power brakes, vac gauge and trans. Based on what everybody is saying is the PVC in that line enough to use off the intake vent hole to prevent the oil issue? The oil fill tube is a vented one. The original breather had no provision for a tube to it either.

 

[Skip FIx]

Yep that is the air intake into the motor. My Trans Am has one into the side of the air cleaner Shaker scoop Base. I think some of the SBC oil fill tubes for PCV had a tight cap and not a breather cap.

 

[1958 delivery]

Yep that is the air intake into the motor. My Trans Am has one into the side of the air cleaner Shaker scoop Base. I think some of the SBC oil fill tubes for PCV had a tight cap and not a breather cap.

"If you connect the PCV to the oil fill tube then you run a sealed cap on the oil fill tube. The rear blow by opening would then go to the bottom of the air cleaner, air flow will be from rear to front.
If you run the pcv at the rear of the carb (vac source) then you use an open oil fill cap so air flow would then go from front to rear "

 

[Don Jacks]

SIMPLE,Run your power brakes,vac gauge off the back of the carb,plumb the pcv to the port in the front of the carb.Beware,that push on oil filler cap ,unless they've fixed it,will not stay on.Use the one from the 327.

 

[Tim]

The 327 one goes on a lot farther and tighter than that chrome one.

 

[rarerodder]

Guys I really like all the replies and info-thanks. My new plan: I'm going to use the 327 fill tube shown below with a twist-on (non-vented) cap,then screw PCV into that and run line from PCV to front carb base vacuum port. Then I plan to use the hole in rear of the intake as vent for air to enter the crankcase by using the grommet/tube from this hole up to the bottom of air cleaner. That should give me rear to front air flow.


Now, one more question that keeps nagging me: Wouldn't that vent tube into the rear of the intake work better if it vented somehow to atmosphere rather than into the air cleaner? Seems to me that the air inside the air cleaner is being suctioned into the carb which would also put suction to this vent tube-opposite to the direction the air needs to flow thru the tube?