PCV system
From Crankshaft Coalition Wiki
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| + | ==Why a PCV system is needed== | ||
| + | Positive crankcase ventilation (PCV) is needed to help remove the acidic gaseous buildup inside the crank case. This is caused by combustion gas blowby around the rings as well as fumes released as the oil gets hot. It also helps ring seal by creating a slight vacuum below the rings. | ||
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| + | ==History== | ||
| + | Before the PCV system road draft tubes were used. This basically vented the gasses directly to the atmosphere. This was major source of smog in big cities and an initiative was launched to solve this. GM invented the PCV system and "gave" it to other manufacturers to use. This was the first emissions control device on automobiles and it drastically reduced the smog problem. | ||
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| + | ==Typical configuration and components== | ||
| + | There are only a few components involved in the PCV system. | ||
| + | * A breather is located in one valve cover through a rubber grommet. This allows fresh air to enter the engine. There are two popular ways to do this. | ||
| + | ** A tube that connects the valve cover to the air filter. | ||
| + | ** Or a small air filter/breather that pushes directly into the hole in the valve cover. | ||
| + | * The PCV valve itself is located on top of the valve cover opposite the one with the fresh air intake, usually through a rubber grommet. | ||
| + | ** The area inside the valve cover below where the grommet is located should be baffled. This helps to avoid oil getting sucked into the PCV valve. | ||
| + | * A rubber hose that connects the PCV valve a vacuum source, usually at the front of a carb or into the plenum area of the intake, not routed into an individual intake runner. | ||
| + | * This setup allows fresh air to enter one side of the engine, go through crankcase, and be introduced into the intake tract. | ||
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| + | You should avoid attaching the breather tube and PCV to the same valve cover. This will not vent enough of the combustion gases. | ||
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==PCV valves for modified engines== | ==PCV valves for modified engines== | ||
| − | Big cams with low idle vacuum throw can throw off a stock PCV valve, creating a lean idle. Normally at idle the PCV is in the low flow position. But if the PCV valve is open at idle (because of low idle manifold vacuum caused by a big cam), the idle gets lean and unstable and may suck too much oil along with too much air. This is akin to a big vacuum leak at idle because the PCV is open at idle instead of in the idle (low flow) position. | + | Big cams with low idle vacuum throw can throw off a stock PCV valve, creating a lean idle. Normally at idle the PCV is in the low flow position. But if the PCV valve is open at idle (because of low idle manifold vacuum caused by a big cam), the idle gets lean and unstable and may suck too much oil along with too much air. This is akin to a big vacuum leak at idle because the PCV is open at idle instead of in the idle (low flow) position. |
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| + | ===PCV on a turbocharged engine=== | ||
| + | *Hotrodders forum post [http://www.hotrodders.com/forum/correct-way-plumb-pcv-system-turbo-car-247049.html The correct way to plumb a PCV system on a turbo car] | ||
==PCV valve specs== | ==PCV valve specs== | ||
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==DIY catch can== | ==DIY catch can== | ||
| − | *Catch can if used need at least a 3/8" connectors and baffles inside. Without some sort of baffle inside the catch can the engine will suck up some oil. | + | *Catch can if used need at least a 3/8" connectors and baffles inside. Without some sort of baffle inside the catch can the engine will suck up some oil. Avoiding oil is important because it will create carbon deposits on valves, pistons, and combustion chambers which hurts performance and can cause preignition when the carbon gets hot. Oil vapors also are a source of detonation which can destroy pistons. |
| − | The catch 'bottle' below is made from an air compressor oil separator. | + | The catch 'bottle' below is made from an air compressor oil separator, it is a cheap alternative to commercially available off the shelf units. |
[[File:Pcv catch1.jpg|250px]] | [[File:Pcv catch1.jpg|250px]] | ||
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==Fixed orifice PCV system== | ==Fixed orifice PCV system== | ||
The LQ4 6.0L crate engine from GM comes with a fixed orifice in the valve cover. The paperwork says to throw the original PCV valve away and connect the hose to the nipple. It appears they are finding the correct size orifice for the engine vacuum and are no longer using a valve. Perhaps a small inline needle valve to adjust crankcase vacuum flow might be the ticket. Not too much to cause a major leak, just enough to evacuate the crankcase. | The LQ4 6.0L crate engine from GM comes with a fixed orifice in the valve cover. The paperwork says to throw the original PCV valve away and connect the hose to the nipple. It appears they are finding the correct size orifice for the engine vacuum and are no longer using a valve. Perhaps a small inline needle valve to adjust crankcase vacuum flow might be the ticket. Not too much to cause a major leak, just enough to evacuate the crankcase. | ||
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| + | A fixed orifice system may not work in all applications, especially forced induction. The pintle valve acts a check valve allowing pressure to move one direction. Likewise, the pintle valve system acts like a spark arrestor, preventing any combustion gasses from entering the valve cover should a backfire occur. | ||
==High tech adjustable PCV== | ==High tech adjustable PCV== | ||
For those who can spend ~ $130.00 for an adjustable PCV valve, this might fit the bill: | For those who can spend ~ $130.00 for an adjustable PCV valve, this might fit the bill: | ||
[http://mewagner.com/ M/E Wagner] | [http://mewagner.com/ M/E Wagner] | ||
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[[File:M-E Wagner Cutaway-3-views.jpg|250 px]] | [[File:M-E Wagner Cutaway-3-views.jpg|250 px]] | ||
[[File:M-E Wagner pcv1.jpg|250 px]] | [[File:M-E Wagner pcv1.jpg|250 px]] | ||
| + | ==Alternatives== | ||
| + | * Road draft tube: should be avoided | ||
| + | * Venting to the exhaust: instead of feeding the crank fumes to the carb, and hard line can be run to the exhaust. The escaping gas creates a low pressure enough to draw the fumes out of the engine. This is a slight improvement on the road draft tube, but complete burning of the byproducts will not occur. Deposits on your exhaust system is likely and if you go this route be sure to plumb the line downstream of any catalytic converts and O2 sensors. The EPA will not like this and is more than likely illegal for street use and will not pass local inspections. Check your applicable laws before proceeding. | ||
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<br><br> | <br><br> | ||
[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Undeveloped articles]] | [[Category:Undeveloped articles]] | ||
[[Category:Undeveloped Engine articles]] | [[Category:Undeveloped Engine articles]] | ||
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