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Let's just hope that they got it right this time because I've just installed the kit. Incidentally, with judicious wiggling, it is possible to remove the oil trap without having to undo anything else, at least on my '99.
I've looked the new system over, and it looks like it works as follows: (Some of this is supposition. I think it's right, but can't be sure without doing some actual pressure measurement. If someone has better info, please post it).
The crankcase vent system has two pathways
a. Path 1: A small hose from the valve cover to the bottom of the throttle body. A check valve allows air to flow only from the crankcase to the throttle body. This is the normal crankcase vent system used on older models and most non-turbo cars.
b. Path 2. A larger hose from the valve cover to the intake side of the turbo via the oil separator. A T from this hose leads to the oil filler tube with airflow only allowed into the oil filler. The oil filler is at the same pressure as the crankcase for all practical purposes.
Consider three cases.
1. At idle, or cruising with no or minimal turbo boost
a. Manifold pressure is lower than atmospheric pressure
b. Pressure on the intake side of the turbo is slightly below atmospheric
c. Pressure inside the crankcase is somewhat above atmospheric because of blowby.
Path 1 (little hose to the throttle body) is open and crankcase gasses flow into the throttle body thereby venting the crankcase.
Path 2 (larger hose from to intake of turbo via oil separator) has some flow because the intake side of the turbo has somewhat lower pressure than the crankcase. The balance between Path 1 and Path 2 depends on the magnitude of the pressures and the flow restrictions imposed by hose size, etc.
2. Turbo boosting to above atmospheric pressure
a. Manifold pressure is higher than atmospheric pressure
b. Pressure on the intake side of the turbo is lower than atmospheric
c. Pressure in the crankcase is substantially higher than atmospheric because of blowby.
Path 1 (little hose to the throttle body) is closed and the check valve prevents manifold pressure from pushing intake air into the throttle body/intake manifold.
Path 2 (larger hose from to intake of turbo via oil separator) is open because the pressure in the crankcase is higher than on the intake side of the turbo. The crankcase gets vented through this route.
3. Decelerating with throttle closed after period of higher RPM running
a. Manifold pressure is very low
b. Pressure on the intake side of the turbo is ~atmospheric
c. Pressure in the crankcase is probably close to atmospheric because there’s little blowby.
Path 1 (little hose to the throttle body) is open because the manifold pressure is low and crankcase gasses are being sucked into throttle body. However, because there’s little blowby, Path 1 can draw crankcase pressure down toward the low manifold pressure.
Path 2 (larger hose from to intake of turbo via oil separator) Probably has little flow because pressure differences aren’t large. In the event that path 1 produces a pressure in the crankcase below atmospheric, the check valve in the hose leading from the oil filler to the Path 2 hose will open and allow intake air into the crankcase which then flows through the crankcase and then through Path 1 to the throttle body/intake manifold.
posted by 70.56.5...
, Sun, 24 Sep 2006 10:32:06
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