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turbo and intake vacuum 900 1993

posted by  darmstrong on  Mon Jan 17 14:03 CST 2005
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last visit: Sat Sep 13 12:21 CST 2014
[RELATED]

My understanding of a normally aspirated engine, is that while the engine is running, a vacuum exists starting from the intake manifold, and extending right on back past the AMM, due to the sucking action of the piston's intake stroke. This vacuum is used to drive the brake booster, positive crankcase ventilation, climate controls, etc.

I'm therefore confused when thinking of how a turbo impacts this. If the turbo compresses the air going into the throttle (ie. positive pressure instead of negative vacuum pressure), then how can there still be vacuum at the throttle body to run the brake booster, PCV, etc.? Or does the turbo just reduce the vacuum to a smaller value, without actually turning it to positive pressure?

If indeed the turbo only lowers the vacuum level, as I'm guessing, does this reduction in vacuum affect things like brake servo, or positive crankcase ventilation, etc., in any way?
--
David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto, ON






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