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During run-up checks, we set the Throttle such a manner that RPM IS 2000 then we do run-up checks

  1. Magneto check 2.prop check
  2. Notice RPM drop
  3. MAP increases
  4. Oil pressure decreases

Why does MAP INCREASE AND OIL PRESSURE DECREASE ?

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When you do the prop cycling check, pulling it to min RPM and having the prop make that cool "zzzhheewwww w w w w w w" sound, manifold pressure goes up because of the reduction in air velocity in the intake ducts as the big air pump that is the engine slows down. Basically, the vacuum level goes down, which is an increase in manifold pressure closer to ambient.

The oil pressure decrease is from the oil flowing into the propeller to drive the blades toward low pitch.

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