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jspilot said:you are reducing the engine power which in turn reduces the air flow through the intake which increases manifold pressure....slower velocity - higher pressure......well at least it sounds good!!
flyifrvfr said:Can someone please tell me why manifold pressure increases when you decrease RPM'S when you are doing a run-up
UnAnswerd said:It doesn't actually increase, technically. You see, anyitme the engine is running, the pressure within the manifold will be lower than atmospheric pressure. We tend to think of it as a "vacuum". But "vacuum" isn't really the best term, because the pressure inside the manifold is not negative, it's just lower than atmospheric pressure.
When you close the throttle, the downward moving pistons are pulling this "vacuum" against a restriction. The actual pressure in the manifold decreases, but the pressure differential or so-called "vacuum" within the manifold increases.
Yellow Snow said:Keep trying you're closing in on it. Think about turbo charged engine though might have to rethink this.
UnstableAviator said:When you reduce the engine RPM, you reduce the engine's demand of air. Since the throttle position hasn't changed, the air will in effect "back up" in the intake tract thereby causing a pressure increase. It is just like Bernoulli's principle in reverse to the way we commonly think of it; Slower moving air exerts a higher pressure.