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Originally Posted by quickdiversion
There is no need to dyno the facts. The facts are in the simple mechanics of how a motor works.
I'll explain this again.
When a motor is at idle, the pcv valve is used to allow the crankcase to pull in small amounts or air into it. This method is used at idle because there is no vaccum on the system.
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This is the way I understand it,
When a motor is at idle, the pcv valve is used to allow the intake manifold to pull vacuum on the crankcase (my car idles at 20mmHG). The restrictor and check ball prevent too much oil getting into the IM, and prevents boost from entering the crankcase.
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When you hit the gas the car goes into vacuum in order to run, I won't get detailed about that. Now the vacuum pulls the pcv valve closed and now must find it from another source. This is where the large tube by the turbo comes in.
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doesnt make sense to me, the PCV check ball closes under boost, not under part throttle vac. My car has vacuum from idle until 20% throttle. Once this checkball is closed and the engine is in boost, the crankpressure is directed straight out a breather to atmosphere, so it doesnt build up any pressure.
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Now, the engine mechanics part again.... If the motor can not pull vacuum under throttle, the pressure will rise in the crank case from the force of the motor pounding away at the air under the rotating assembly. To much pressure and pop go yout rings, and other things.
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This also doesnt make sense to me, because I was wondering about a atmospheric PCV is not sealed so no pressure builds up in the crankcase at all.
Interested in your thoughts. It's a trivial matter to unhook the hose on the dyno and actually get some real evidence, so I will be sure to do that as soon as I can
The way I see it, pulling 20mmHG(.4psi) vacuum on the crankcase VS none at all will only change the pressure differential of the crankcase/combustion chamber by 2%, hardly enough to notice.