What is that a pump thats connected to the valve cover what is it called and what does this do ive seen them on cars but dont know what the purpose of that part is for can someone explain thanks.
What is this
- Thread starter 79MaliCrazz
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Scavenge gases/pressure from the crankcase, helping the rings seal on high power engines. In OEM form, it's accomplished by a vacuum port on the base of the carb pulling through the PCV (positive crankcase ventilation) valve - purpose is to reduce hydrocarbon emissions by pulling unburnt fuel that makes it past the rings and putting it into the combustion stream. On old 265/283 engines, there was no pump, just a simple pipe that came up by the thermostat with a breather cap.
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Crankcase Evacuation Pump (vacuum pump) designed mainly for drag racing to help seal low tension oil rings and reduce crankcase pressure.
The inexpensive version would be a breather in each valve cover with a hose running to a check valve that is mounted to an angled pipe welded in the header collector, when the exhaust passes by the pipe it pulls vacuum relieving crankcase pressure.
I use a Moroso pump on my 565 BBC to help relieve crankcase pressure on high rpm blasts even though I am running standard tension oil rings.
I converted to this set up for consistency since after changing to larger headers the standard header evac. system that I was running became inconsistent.
You would also want to use a relief valve either mounted to the valve cover or to the vacuum pump itself so you can adjust how much vacuum it pulls, this set up is a closed system so there no breathers on the valve covers.
You can see the relief valve on the back of the drivers valve cover, vacuum gets pulled through the pump and exits the breather set up on the passenger side.
The inexpensive version would be a breather in each valve cover with a hose running to a check valve that is mounted to an angled pipe welded in the header collector, when the exhaust passes by the pipe it pulls vacuum relieving crankcase pressure.
I use a Moroso pump on my 565 BBC to help relieve crankcase pressure on high rpm blasts even though I am running standard tension oil rings.
I converted to this set up for consistency since after changing to larger headers the standard header evac. system that I was running became inconsistent.
You would also want to use a relief valve either mounted to the valve cover or to the vacuum pump itself so you can adjust how much vacuum it pulls, this set up is a closed system so there no breathers on the valve covers.
You can see the relief valve on the back of the drivers valve cover, vacuum gets pulled through the pump and exits the breather set up on the passenger side.
Will this prevent oil from blowing out the dipstick tube when hitting high rpms. Seen it happen a few times. Mainly oil and vapors. Not just a stream of oil.
If the crankcase becomes pressurized, the path of least resistance is where the pressure will equalize. That's why when you flip and OEM vavle cover over, there is a baffle under the PCV and breather fittings, in case the engine builds up pressure and backs up the normal path. Gases turn corner much better than liquids, so the oil hopefully stays in the crankcase, and only the gases escape. If there is some oil and a dipstick in the way, out they come!
When I had my 496 BBC it would blow the pvc right out of the valve cover when I would hit 6800-7000 rpm and of coarse it would idle high right after since I now have a vacuum leak and that is when I started using the tradition header evacuation set up which works well in most cases if set up right.
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