PCV plumbing

[John]

PCV plumbing for a 348 tri power how to plumb it? Road draft tube to base of center carb with a pcv. Is that enough? Thanks John:confused:

[IgnitionMan]

You also need an air entry point for the circulatory system.

Usually, it is on the other side of the engine, valve cover, from the PCV.

I remember my 1964 Impala SS with 327 had a hose fitting in the road draft tube hole in the rear of the block, had a hose on it that went to the air filter base, for the clean air inlet, and from the oil filler tube, sealed twist on filler cap, PCV valve screwed into the tube, then to the carb base vacuum fitting. No holes on either valve cover.

I have seen different year oil filler tubes with no PCV hose fitting, a screw in boss and a simple hose nipple, for an inline PCV with hose nipples on both ends.

But, no matter how it's done, there has to be a free air inlet and a PCV fitting so the air can circulate. A PCV valve alone won't do what the system wants done.

[29Coupe348]

im running a pcv valve where the road draft tube went, and plumbed it to the rear of the center carb, and i also rum my transmission vacuum off that, and i have had no prblems.

[IgnitionMan]

Well...OK, but...if there is no way for fresh air to enter the air/oil windage areas inside the engine, then the PCV doesn't get air to flow through it, now does it!

A PCV system HAS to have some form of fresh air inlet to function, and not even correctly if the wrong PC valve vacuum weighting is used, AS IT IS A CURCULATORY TYPE SYSTEM, NOT A STATIC ONE.

Now, TEST you can do to prove what I wrote, seal off a non-collapsable cup of water, with a straw sealed to it, with liquid in it, so only a vacuum can be placed to the straw by su-ck-ing on it. Now, su-ck on it, don't get much liquid up the straw, do you (remember, NO vent in the cup, top or straw), lack of available air flow into the cup stops the liquid and air flow up the straw! Your engine is doing the exact same thing if there isn't a way to get air into ot for the PCV system to flow it.

THAT is the way your particular non-air inlet vented PCV system is not working correctly.

The reason your system "hasn't had a problem" is, it doesn't have a complete PCV system, with functioning air flow, correctly valve'd or not. It is doing nothing, useless without a fresh air inlet to complete it.

[29Coupe348]

i have a breather on my oil fill tube on the front of the intake....i figured that would be a given on these motors, because there is no holes in the valve covers.

[IgnitionMan]

Aha!, Yes, THAT definately qualifies as a fresh air inlet, and your system is golden. Later years used the oil filler tube with a sealed off cap for the PCV system, then, they started putting holes in the rocker covers and messed the whole looks of the engines right up.

[John]

Thanks a lot for the help. I didnt do the suck on the cup trick just took your word for it. Now I have to decide how i want to vent and still like the way i did it. Probably oil fill spout with a vented cap. 348 is built and just waiting for the new water pump. again thanks guys John:cheers