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Posted by: robkammer Dec 8 2021, 02:10 PM

I'm in process of cleaning up all of the electrical and vacuum lines in the engine bay. The car does have a check valve of sorts, maybe a PCV. I read differing accounts of whether or not a 74 should have one or should it just be plumbed without?
And I've gotta say, it sure looks nice in there without any vacuum lines!
Rob

Posted by: 914_teener Dec 8 2021, 03:12 PM

You should run one IMHO. Otherwise stock up on valve cover gaskets.

Posted by: emerygt350 Dec 8 2021, 05:04 PM

The 74 was a passive vent system into the air cleaner. I prefer the positive flow on my motors (like the 73) but if passive was good enough for Porsche/VW...

You need it.
1) you don't want to vent that to atmosphere
2) gaskets
3) engines last longer if those gases are not in there too long.

Posted by: KELTY360 Dec 8 2021, 08:34 PM

PCV not PVC

One is a valve the other is plastic pipe.

Posted by: JamesM Dec 9 2021, 03:16 AM

Not sure exactly when the changeover was, but every 74 I have had has the PCV getting suction from the plenum. 75+ had the larger passive vent to the air cleaner.

To properly remove it though you will need to swap both your plenum and airbox to later parts.

I think there are pros and cons to both, the biggest con of keeping the PCV now is that new/good ones are near impossible to come by.

Post pics of your plenum and I can tell you what you have.

Posted by: emerygt350 Dec 9 2021, 05:39 AM

The last 74 I looked at was passive but perhaps it had been messed with.

Posted by: robkammer Dec 9 2021, 08:50 AM

Thanks guys. This isn't the best picture, looks like a valve but confirmation would be good.

Posted by: BeatNavy Dec 9 2021, 09:36 AM

That little circular thing next to the oil (or "oel") filler neck is indeed a PCV valve.

Posted by: emerygt350 Dec 9 2021, 11:49 AM

Clean it up and plug her in....

Posted by: JamesM Dec 9 2021, 08:39 PM

That is indeed an early crank case vent system/PCV valve.

It looks like your intake plenum is the later style though (based on the thicker throttle cable bracket) and that presents a bit of a problem as the later style does not have the port necessary to attach the CCV to it.

You can verify this by checking the two ports on the side of the plenum. The late style has a large and small port, the early style that is needed has two larger ports.

Not sure what airbox you have but you will need the matching early style as well.

Posted by: r_towle Dec 9 2021, 11:01 PM

Yes, but pvc could be pcv

Posted by: robkammer Dec 11 2021, 04:47 PM

Dislexia is not something to laugh at. Although feel free to laugh at me! Positive Crankcase Ventilation from the 70's,
Sheesh