PCV Clarification

[cortcomp]

I've been researching the PCV system on my truck (california emissions '66)

From what i read and how it was hooked up, it was basically the rear vent port to the air cleaner, and then the PCV in the filler tube to the manifold, and a non-vented cap on the oil fill.

I am going to somewhat re-create that (with a rear vent to the drivers side and putting my own connection into the air cleaner with flame arrester, since my passenger side oriented vent tube was mangled and i don't need it's A.I.R. system bracket, and my air cleaner doesn't have any fittings yet.)

In the pic below, basically the bottom setup is what i think i'm aiming for. My questions are (and sorry if it's been covered, haven't found answers searching):

1) In the diagram, they don't show a PCV but show a metered orifice. My fill tube has the threaded port for the PCV valve and i have one in there. Assuming that the PCV acts as the orfice and i can just connect the rubber line from it to manifold vacuum?

2) I see a lot of guys going the other way, rear vent to pcv to vacuum, and the front with the vented filler cap (basically top in the pic below). Does it matter? I have the parts for the second option and it is kind of closer to original for my truck.

[Paul Y]

Personally I would go with option 1.

The PCV basically acts as a one way valve to stop anything from the manifold finding its way into the engine (blow back etc). The metered orifice is there to create a greater draw, so the PCV will and can replace it.

You will need a vented cap to stop the creation of a vacuum within the engine. Without it the engine will find its own source of fresh air!

The lower picture pulls air in from the cleaner so that would not need a vented cap...

Would vent the PCV into the manifold rather than the air cleaner, especially if your motor is breathing a bit heavy...

Not sure if that helps or not!

P.

[markeb01]

I did several “Smog Control” kit installations back in the mid-1960’s before smog systems became mandatory on newly produced cars. The lower set of instructions look much like the aftermarket kits.

For a while California required (mandated) all cars have smog controls, which sent quite a few older cars straight to the junk yards. There was no PCV valve, just a “metered orifice” that was essentially a raw vacuum leak. This caused the engine to run rough and burned the intake valves. The “flame arrestor” was a chunk of wire brush that was stuffed in a hose, and was supposed to prevent exploding the crankcase in the event of backfire. The greatest damage however was caused by drilling a hole in the intake manifold and pounding a lead plug/adapter in place to connect the vacuum hose.

Many unethical mechanics drilled that hole with the manifold in place, sending shavings and debris right into the intake valve seats, cylinders, and rings, ruining the engine in short order. On the ones I did, I at least removed the intake manifold before drilling! These early (ruin your car) smog systems were responsible for much of the resentment against smog controls when finally implemented by the big 3.

However you choose to route the connections, never run a system without a PCV. It remains mostly closed at idle and keeps the engine idling relatively smoothly. A metered orifice system does not adjust to engine vacuum and simply leaks all the time.

[chewychevy67]

These are the pieces for 66 67 small block to do a closed pcv system without A.I.R. which is option K24 except the hose between the pipe and cleaner base. I am not sure about the metering valve in 67 but could very well be in 66. 67 had a pcv valve threaded into the tube. the brass fitting goes into the rear of the carb not the intake manifold. this in my opinion is much nicer set up than the standard breather cap set up.

[cortcomp]

That is the exact setup i have except my repop air cleaner doesn't have the tube yet, i found one i can install and glue the spark arrestor inside the air cleaner. If it works that's good enough for me since i have those parts in hand, i just wanted to make sure that i wasn't missing a piece to the setup.

Thanks all of you for your info!

[chewychevy67]

if you do use a pcv instead of a metering block it uses part CV726C. I emailed you some pic's of my 67 A.I.R. 327 as well.