How is vacuum created in engine if intake is open to atmosphere?

[freeonboard]

Is the air filter one way check valve? Thanks. Losing sleep over this.

[seang]

The ait filter is not a check valve. Factory engines sacrifice lots of top end flow in order to enable some vaccum to be present in the intake manifold, (and subsequently the vaccum accessories), during normal driving. The camshaft specs have a LOT to do with how much vaccum is present at certain rpms. When the intake valve opens up, the piston pulls in air rather violently, it doesn't need a check valve. I can't quite find the proper words to say about this, I hope someone else can be of some more help. Maybe the engineering thread.

[480sx]

Losing sleep because of throttle bodies and IACV's?

[DaniMike]

How do the vacuum accesories work if FI?

[seang]

Every engine pulls in air the same way, whether it be FI, carb, ram air, and even forced induction (this is the N/A forum though). There is a check valve on the brake booster, however, to hold the vaccum charge once its there. All the other accessories read the vaccum as it changes, and adjusts accordingly, things like ignition timing, EGR, MAP sensor, and various others. This is very general, and every engine has its own anomalies, but essentially, they all work the same way.

[landygrundy]

an engine is just a big air pump, vacuum is created when there is a pressure difference. when the piston goes down your created a low pressure area.. thus the atmospheric pressure is much greater... creating vacuum. just like sucking on a straw in water... you create a low pressure area when you breath in.. the pressure at the bottom of the straw is greater... creating vacuum, and moving the water up the straw. so if it wasn't "open" to the atmosphere.. no vacuum could be created. the basic principal of how a carburetor works aswell(pressure differences)

[DaniMike]

How does this apply if the turbo is pushing air/ adding pressure? How can it still have a vacuum? I am sooo confused..

[RCA]

How does this apply if the turbo is pushing air/ adding pressure? How can it still have a vacuum? I am sooo confused..

Well I am no engineer but my logic tells me:Boosted applications will not have vacuum when boost is reached. As a matter of fact Boost gauges are some times split into two "sections"...Boost and vacuum. You can't be in both. Either you're in boost and then once throttle it released, and excess pressures are released via blow off valve does the gauge return to it's natural state of vacuum.