PCV Question

[AU Doc]

Can I route my passenger side valve cover vent to this port on my TB?

in my rush to get my engine running, I completely forgot to hookup my vent.

[badazz81z28]

That tube is meant to pull fresh air in. As long as the air source is metered (tapped after the MAF), it will be ok. That air will make its way back into the intake. What’s currently hooked to that port? I have mine blocked off in a retro swap.

[AU Doc]

Awesome. Thanks for the response!

Yes. The port on the TB is currently blocked. I just grabbed a piece of fuel line and stuck a bolt in it until I could cap it properly. But now I have something I can do with it :-)

[dhutton]

I would have thought you would want that connection on the other side of the throttle body but I am no expert. Hopefully our favorite expert will chime in...

Don

[parsonsj]

No -- you don't want to do that. First off, that's not a vent port on the valve cover. That's the fresh air inlet.

You want to connect that to clean fresh air somewhere in your intake tube after the MAF, but before the throttle plate.

[AU Doc]

Can you explain the difference in plumbing this before vs after the throttle blade?

I don’t have a MAF (I doubt that matters here). I’m running a Holley EFI

I only ask because I would have to have a nipple TIGed to my intake pipe. I would have to get someone to do that for me.

[dhutton]

Pretty sure there is no pressure differential between that port and the port the other end of the crankcase ventilation system is tied to. Hence no air flow....

At least that is my thinking. Expert opinion still needed.

Don

[parsonsj]

PCV = Positive crankcase ventilation. V8s typically implement this by routing fresh clean air from the intake tube into the engine on one valve cover, and pulling dirty air from the other valve cover via the PCV valve. In order to get the air going in the right direction, engine vacuum is used to pull it from the dirty side, which pulls the clean air into the other side.

Connecting the nipple past the throttle blade means you are connecting to vacuum.

If you connect the clean air side to engine vacuum, both sides are pulling vacuum and there's no ventilation. Your PCV won't work at all.

[AU Doc]

Above is a pic of the passenger side of the TB. This engine is a vette pull out, and I think this is the factory routing. The port on the drivers side valve cover has a cap on it, and the port on the back of the intake.

If I understand your description correctly, can I just cap that vent on the passenger valve cover and put a filtered breather on the oil fill neck?

[dhutton]

Should be ok since you don’t have a MAF.

Don

[parsonsj]

Yes, that will give you the required clean air flowing through the PCV. No MAF, so no need to measure the total airflow into the engine.

[79 Camaro]

As I under stand the port on the drivers side was for the gas tank vapor solenoid. I typically cut the nipple off and than drill and tap it for a plug.

[parsonsj]

Right, it's just a vacuum port used for vapor purge. I usually just put a vacuum cap on it. (hadn't thought about tapping it -- I might steal that idea)