PCV Theory ?

I finally was able to take the '61 with TriPower 250 for a reasonable cruise with a few of the family. After ten years of upgrades, cruising the interstate at high speed with family in traffic had me reviewing all my work on safety related components. After a couple hundred miles my confidence is reassured but inspection revealed the valve cover breather came off.

I thought I knew it all :roll: so I have a question:

I hadn't thought about it before but the 250 has an intake vacuum PCV on rear VC port. The setup as built had a typical vented front VC breather port/cap as well. Shouldn't an operable PCV system not use a vented port on the VC?. Better to use a non-vented cap ?. I thought the "closed crankcase venting" PCV system needed closed vacuum to work properly?. This performance built engine is intact as built years ago but has components and build specs that add bit of a mystery.

Thamks

The PCV system definitely needs an open vent on the valve cover. Usually it's the oil fill cap, and often times this is connected to the clean air side of the air filter. The valve cover has a sealing plate that is designed to limit air flow directly from the vent to the PCV.

The PCV system is sometimes criticized as some kind of power robbing smog system. In reality, it's function is to keep the engine clear of moisture and other combustion products that seep by the rings. Without a vent, the high vacuum from the PCV would encourage blow by from the rings. Not a good thing.

John/Fresno

i got rid of my pvc system since it seemed to take away power but now my oil go's black after like 2 weeks, im looking into getting a vac pump of some sort or crank evacuation kit, im leaning more to the vac pump http://lightningmotorsports.com/i-298096.aspx

8) PCV stands for positive crankcase ventilation. it does not mean a closed system. some PCV systems use an open breather in the valve cover, others use a tube that runs from the air cleaner to the valve cover. however all use intake manifold pressure, well vacuum, to draw crankcase air into the combustion chamber to burn off the blow by from the cylinders to reduce emissions.

One of the biggest byproducts of combustion is water. If you remove the PCV, that moisture stays in the block where it contributes to acid and sludge formation.

You need a source of fresh air to replace the air sucked out by the PCV, either from the air cleaner or a breather. It might be better if the air were coming in from someplace else and all the fumes were evacuated from the block, but something is better than nothing.

Good read.

http://www.britishv8.org/Articles/Posit ... on-PCV.htm

If you have the time an patience, the PCV topic linked below was eye-opening for many of us. Some portions mention vented vs non-vented caps.
Doug

viewtopic.php?f=5&t=53111&hilit=+PCV