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Discussion Starter · #1 ·
So can anyone confirm with a proper running 1.8t if the crankcase is under vacuum or pressure at idle???

Just curious as I plan on replacing some of thhe crankcase breather parts on my car and I would like to know what the baseline crankcase behavior is.
 

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Gustav
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Vacuum 20-25 inches of mercury at idle properly running. Boost creates pressure so the air going into the cylinders is pressurized.
There for if you run 8 psi of boost to your 9.5:1 compression ratio engine your actual CR is 14.67:1
This is why under high boost the factory connecting rods fail.
Sorry if I gave you too much information :confused:
 

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Discussion Starter · #3 ·
The question was is the crankcase under a vacuum or pressure at idle?

The reason I ask is this may be useful for people to determine if the crankcase venting and PCV valve are function properly.

I expect a small vacuum in the crankcase, but just curious what others have found in real world experience. Say cracking the oil fill cap? or checking at the dipstick tube.
 

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Gustav
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349 Posts
The question was is the crankcase under a vacuum or pressure at idle?

The reason I ask is this may be useful for people to determine if the crankcase venting and PCV valve are function properly.

I expect a small vacuum in the crankcase, but just curious what others have found in real world experience. Say cracking the oil fill cap? or checking at the dipstick tube.
Crank case is neutral the vacuum that is used to vent to the PCV system comes from from the intake system. If you open the oil cap or pull the dip stick while the engine is running it will not be pulling vacuum or loaded with pressure. If it is then you have a issue with your engine!
 
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