Re: Now here is an interesting item
the stock system either the road draft tube or the PCV valve was to remove the oil vapors from the crankcase but the header collector or even a vacuum pump on the engine or built into the dry sump oil pump is to create a vacuum in the crankcase to cut down on the windage inside the engine.they are so efficient that you need to use pressurize oil to oil the piston wrist pins to prevent them from seizing. it also allows the use of light tension oil ring expanders so the engine will develop more HP do to less friction caused by the rings. without the external vacuum source the light pressure oil ring expanders would allow too much oil left on the cylinder walls and you would have oil getting into the combustion chambers and causing a burned piston.
No matter how precise and well built an engine is, THERE WILL BE a certain amount of blowby (combustion pressure going down the cylinder walls past the piston rings). This blowby puts (depending on the wear condition of the engine) pressure in the crankcase. My whole point here is that it IS NOT necessary for a fresh air source entry point for the crankcase. All that is NECESSARY is an EXIT point for the pressure buildup resulting from blowby. If no exit point existed for this pressure in an engine-------------THE SEALS AT EACH END OF THE CRANKSHAFT WOULD BLOW OUT------------and that has happened to a few unfortunate folks who did not understand this!
In fact, there ARE some engines that DO NOT provide an inlet source for crankcase air, only an exit-----------by way of a PCV valve!
Engines prior to 1963 (62 in Calif), a road draft tube system was used to allow vapors/pressure to escape. As the vehicle moved along the roadway, the air passing over the end of the road draft tube (notice road draft tubes are always angled toward the rear of the vehicle) created a vacuum and sucked out the vapors/pressure. Then in 63 (62 for Calif) a positive crankcase ventilation (PCV) system was installed on all engines. And some auto manufacturers sold retrofit PCV kits to install on older vehicles. The early PCV systems had an inlet (usually a breather type oil fill cap) for fresh air and a PCV valve plumbed into the fuel intake (usually the base of the carb, or FI plenum). Shortly thereafter, the fresh air inlet was a hose between the air filter and the crankcase so that clean, filtered air, instead of unfiltered outside air, was introduced into the crankcase. But all of the crankcase vapors/pressure (now dirty air) were STILL sucked into the intake manifold by way of a PCV valve. On heavily worn engines, or engines that are subjected to severe duty (ie racing) conditions, that little ole PCV orifice just is not sufficient to allow excessive pressures to escape from the crankcase. So, guess where they go???
Anyone ever seen headers on a race car where there is a hose running from each valve cover to a check valve plumbed into the header collector? The header collector is sucking all that high pressure blowby out of the crankcase!
In fact, there ARE some engines that DO NOT provide an inlet source for crankcase air, only an exit-----------by way of a PCV valve!
Engines prior to 1963 (62 in Calif), a road draft tube system was used to allow vapors/pressure to escape. As the vehicle moved along the roadway, the air passing over the end of the road draft tube (notice road draft tubes are always angled toward the rear of the vehicle) created a vacuum and sucked out the vapors/pressure. Then in 63 (62 for Calif) a positive crankcase ventilation (PCV) system was installed on all engines. And some auto manufacturers sold retrofit PCV kits to install on older vehicles. The early PCV systems had an inlet (usually a breather type oil fill cap) for fresh air and a PCV valve plumbed into the fuel intake (usually the base of the carb, or FI plenum). Shortly thereafter, the fresh air inlet was a hose between the air filter and the crankcase so that clean, filtered air, instead of unfiltered outside air, was introduced into the crankcase. But all of the crankcase vapors/pressure (now dirty air) were STILL sucked into the intake manifold by way of a PCV valve. On heavily worn engines, or engines that are subjected to severe duty (ie racing) conditions, that little ole PCV orifice just is not sufficient to allow excessive pressures to escape from the crankcase. So, guess where they go???
Anyone ever seen headers on a race car where there is a hose running from each valve cover to a check valve plumbed into the header collector? The header collector is sucking all that high pressure blowby out of the crankcase!
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