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minnow wrote:
Found this also about the 8.1 internal PCV valve:
Intake Manifold:
The intake manifold is a one-piece design. The intake
manifold is made of cast aluminum. The throttle body
is attached to the front of the intake manifold. A linear
exhaust gas recirculation (EGR) port is cast into the
manifold for exhaust gas recirculation mixture. The
EGR valve bolts onto the rear of the intake manifold.
The fuel rail assembly with eight separate fuel
injectors is retained to the intake manifold by four
studs. The fuel injectors are seated in their individual
manifold bores with O-ring seals to provide sealing. A
Manifold Absolute Pressure (MAP) sensor is mounted
on the top of the intake manifold and sealed by an
O-ring seal. The MAP sensor is held in place with a
retainer bolt. The evaporative emission canister
solenoid is located in the front of the intake manifold.
The positive crankcase ventilation (PCV) system is
internally cast into the intake manifold. There is not a
PCV valve. A splash shield is installed under the
intake manifold. The shield prevents hot oil from
contacting the bottom of the intake manifold, maintaining
air inlet charge density.
The L18 has an internal positive crankcase
ventilation (PCV) system, and does not
utilize a PCV valve.
OK. Now I believe there may not be a valve per se. By that, I mean a serviceable "two speed" bobbit valve. There may be just an unsophisticated fixed port size that is supposed to handle both high throttle blow-by conditions, as well as the former "restricted oriface" for idle conditions.
Still not knowing any more than this, I'm not too impressed by this OEM engineering. And having had my fill of hokey aftermarket hotrod "fixes", I normally attach far more respect to OEM engineering than aftermarket IQ. As it stands, it seems whatever vacuum port size GM chose may become plugged and impossible to service, but that is probably not the case here. The flaw, if any, is probably a case of too much oil going through an over-sized oriface (fixed?) for whatever reason. In keeping with past practice, if the port is large enough for hard throttle, it strikes me as too large for idle.
In this case I might seriously consider adding an external PCV bobbit valve off an older engine. There is one other reason this might help and that is because even the standard PCV valve size often appears inadequate when aging engine wear dictates a serious blow-by increase. I suppose the old valve covers will not fit, but one could theoretically "bolt on" another port to keep up with suitable evacuation of the crankcase. I believe some fixes for DI turbo'd engines have done this, because the excess-blow-by problem is largely the same... an overwhelmed venting system. Some DI/Turbo'd fixes have involved an oil catch can (Something Turtle should be familiar with in his racing career/hobby) to extract oil from vapor going to the intake.
I suppose there is a bit of truth to the claim that big blocks use* more oil, but I don't think Ford's 460 cubic inch V8 suffers quite as much from excess oil use. Logically, oil use should be directly proportionate to engine size, so some increase is expected of big blocks. The 8.1L seems to be notorious for oil consumption (and leaks), and I suspect the revised OEM venting system is to blame. I still wonder why GM changed it.
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* I am a former railroader. Our locomotives constituted a very large big block. I have no idea how much oil they burned, nor exactly how the crankcase vent system worked. I do know that the engines were equipped with crankcase over-pressure safety controls. A broken piston would cause the engine to shut down and require a reset, but we were asked not to do this so that it could be done later by qualified roundhouse personel. The crankcases held about 300 gallons of oil and it took 50 gallons to bring the dipstick from add up to full. The dipstick was therefore a poor measure of oil used by the measly quart. The level was always checked with the engine idling, and I think the most any crew ever dumped in (as an operating crew away from a service bay) was 5 gallons. The oil weight was so thick, it was jokingly said by machinists that one could rest their flashlight on it's surface on a cold, dead engine. There were extreme oil change intervals (years) between changes and the oil is reused indefinately after recycling.
Wes
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