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wayne1234 |
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#1
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Member ![]() ![]() Group: Members Posts: 260 Joined: 6-April 09 From: indianapolis in Member No.: 10,238 Region Association: None ![]() |
Ok dual webber carbed 2.0, I think the PO had the head vents running to a T then to the oil breather near the oil cap... Is this right?? I did a search and now I'm really confused,,,,
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HAM Inc |
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#2
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Senior Member ![]() ![]() ![]() Group: Members Posts: 846 Joined: 24-July 06 From: Watkinsville,GA Member No.: 6,499 Region Association: None ![]() |
The pressure in the crankcase at large is generated in the bottom end, not the heads. The issue with the T4 is that the drain back passages that are just above the lifters in the crankcase are relatively small. If blowby generated crankcase pressure is moving out toward the heads it does so through these small drain passages, making it more difficult for the oil to drain back into the case.
As a side note we experimented with some jaw dropping big vents (over 1.5")on the chimney to see if this would prevent the pressure differential; it did not. Oil still exited the rocker vents. By eliminating the rocker vents you ensure that the pressure in the bottom end is the same (or there abouts) as the pressure in the rocker chambers, which allows the oil to return to the bottom end without fighting a pressure differential at the point of entry into the case. The bottom line is that if you have rocker vents the pressure in the crankcase at the drainback point will exceed the pressure in the rocker chambers, thereby inhibiting oil flow back to the bottomend. Period. The more blowby or full throttle time; the more of an issue this is. Ask yourself why you want your oil to exit the rocker chambers through a hose that then has to run to a vent can and then make its way back to the engine when it could just run back to the case directly through the pushrod tubes. As Jake said a bit more venting at the chimney is in order, though not a lot more seems to be required. (Brent of Raby Enterprises gets the credit for that observation!) |
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