PCV?
- Thread starter ham1974
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PCV.
Typically installed in a valve cover and gets it's vacuum source from a large port at the base of the carb. Some early models had the PCV screwed into the oil fill tube at the front of the intake manifold.
Be sure you also have a breather installed somewhere or it'll suck in gaskets and cause leaks.
Typically installed in a valve cover and gets it's vacuum source from a large port at the base of the carb. Some early models had the PCV screwed into the oil fill tube at the front of the intake manifold.
Be sure you also have a breather installed somewhere or it'll suck in gaskets and cause leaks.
Short answer is yes you want one.
One benefit is hydrocarbon emission reduction - less stinky exhaust, soot stains by tailpipes.
More important is that it purges unspent hydrocarbon buildup in the crankcase (which unchecked leads to backfire through carb/dieseling at shutoff) and, in theory, lessens condensation under the valve covers.
The way it works is imagine a shoebox with a hole on each end. Now, put a vacuum hose on one end - the pcv is the fitting, the hose is the rubber line, and then you use a vacuum source normally off the intake, thats your vacuum cleaner. It sucks whatever is in the shoebox (crankcase via valve covers) out and puts it into the intake to be reburned.
You need that second opening to let the air in to crossflow across, as the vacuum end (pcv) sucks out something you need to replace it. This inlet air needs to be filtered so you don't suck dirt, grit, bugs, debris into the engine to gunk things up and cause premature wear. Can be a push in breather, or a hose running to the air cleaner with a pad on the end/inside. Doesn't matter how you choose so long as 1) the air is being filtered, 2) there isn't a leak allowing unfiltered air and debris to get sucked in behind where the filter is set up, and 3) you keep that filter clean and fresh as much as you would your regular air filter.
EDIT:
Forgot to add some of the originally unintended but very real benefits:
Increases service life of emissions related parts - o2 sensors, cat converters etc
- increases service lives of exhaust parts - mild steel headers at the collectors, muffler baffles, etc
- acts as a pressure vent on older motors experiencing blowby due to ring/cylinder wear.
So even if you're "non-emissions" or "aren't running cats/o2s/no carb to backfire"... run one anyways
One benefit is hydrocarbon emission reduction - less stinky exhaust, soot stains by tailpipes.
More important is that it purges unspent hydrocarbon buildup in the crankcase (which unchecked leads to backfire through carb/dieseling at shutoff) and, in theory, lessens condensation under the valve covers.
The way it works is imagine a shoebox with a hole on each end. Now, put a vacuum hose on one end - the pcv is the fitting, the hose is the rubber line, and then you use a vacuum source normally off the intake, thats your vacuum cleaner. It sucks whatever is in the shoebox (crankcase via valve covers) out and puts it into the intake to be reburned.
You need that second opening to let the air in to crossflow across, as the vacuum end (pcv) sucks out something you need to replace it. This inlet air needs to be filtered so you don't suck dirt, grit, bugs, debris into the engine to gunk things up and cause premature wear. Can be a push in breather, or a hose running to the air cleaner with a pad on the end/inside. Doesn't matter how you choose so long as 1) the air is being filtered, 2) there isn't a leak allowing unfiltered air and debris to get sucked in behind where the filter is set up, and 3) you keep that filter clean and fresh as much as you would your regular air filter.
EDIT:
Forgot to add some of the originally unintended but very real benefits:
Increases service life of emissions related parts - o2 sensors, cat converters etc
- increases service lives of exhaust parts - mild steel headers at the collectors, muffler baffles, etc
- acts as a pressure vent on older motors experiencing blowby due to ring/cylinder wear.
So even if you're "non-emissions" or "aren't running cats/o2s/no carb to backfire"... run one anyways
Last edited:
make sure you get the right one, you can suck in alot of oil if it not the correct one
Even if you aren't running a computer or a bunch of emissions equipment, a PCV is important. During the combustion event, the cylinder space is over-pressured and a tiny amount of combustion gas makes it through the piston rings into the oil pan/crankcase. Do this several thousand times per minute and the inside of the engine becomes positive pressured, including under the valve covers. More gas, more revs, higher pressure, more leak-by. No other piston action creates enough force to relive this pressure. Without a PCV valve, over time, the positive pressure will often cause the engine to leak through the gaskets in order to relieve the pressure. By removing the pressure through the valve covers, the inside of the engine stays, more or less, neutral pressured. Using vacuum from the engine allows the pressure to be relieved and the gasses burned in the engine, without polluting the outside air.
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