Positive Crankcase Ventilation Questions

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Positive Crankcase Ventilation Questions

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Corvette Forum >> Corvette Models >> Corvette C3 Forum >> Positive Crankcase Ventilation Questions

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Positive Crankcase Ventilation Questions - 9/28/2008 9:08:31 AM

piratejosh

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Joined: 7/29/2008
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I had a quick question that doesn''t necessarily have to do with C3s specifically, but I thought someone here might know.

Does forced air induction eliminate the negative pressure in the intake manifold?

Also, what about other situations in which the intake manifold is actually running at higher-than-atmosphere pressure (such as when a turbo is used): how does the Positive Crankcase Ventilation system work in such situations because it only works based on that slight vaccume, right?

I''m still very new to this game, so thanks to anyone who could answer this question!

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RE: Positive Crankcase Ventilation Questions - 9/28/2008 12:08:41 PM

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The PCV valve works on vacuum, it draws the blowby fumes out of the crankcase and recycles them into the carb to be burnt and exhausted out the tail pipe.

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RE: Positive Crankcase Ventilation Questions - 9/28/2008 6:49:02 PM

73shark

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I think his question is, is how does that work when you have say, 10 psi of boost. I think what will happen is that the blowby gas will be forced back thru the pipe that is connected to the air cleaner. That would tend to get oil vapor on the filter element. Have to use a K&N, I guess. Since I''ve never had a boosted engine, can''t really say.

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RE: Positive Crankcase Ventilation Questions - 9/28/2008 8:47:41 PM

Texas Jim

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Joined: 12/15/2005
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quote:

ORIGINAL: pg

The PCV valve works on vacuum, it draws the blowby fumes out of the crankcase and recycles them into the carb to be burnt and exhausted out the tail pipe.

And even w/o vacuum, the pressure in the crank case will blow out of the crank case vent tube (used prior to the PCV).

And if you have oil on your air filter from the PCV, then you have "blow-by; compression leaking past the compression rings and creating "excess" pressure in the crank case-time for a bottom end, or run a vent tube-not to the air cleaner (and pollute alittle). LOL

I do know that when running a turbo, you run lower compression, like 8 or 8.5 to 1 as opposed to a high performance 10 or 10.25 to 1 or higher ratio. I remember this from drag racing bikes years back. I was always into carbs and never got into turbos. You can check on bottom ends built and kits made for turbos, cars and bikes.

(in reply to pg)

Post #: 4