Quote:
Originally Posted by johnmyster
Pumping loss is a result of the energy lost when air moves through the throttle plate, going from atmospheric pressure to a lower, state of vacuum. It's a bigger picture process, but that's where it comes from. It's like uncorking an air tank and letting it spill out into a low pressure surrounding. That energy is lost - not mechanically captured.
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John, you *almost* but not quite hit the nail on the head.
The pumping losses are a horsepower loss measurable at the crankshaft that is consumed by pumping air. The throttling process of the airflow itself has little to nothing to do with pumping losses, except that the greater the throttling the greater the pumping losses. Correlation is not causation.
The pumping loss is the shaft power required to pull air into the cylinder. Nature abhors a vacuum yet atmospheric or lower air pressure does nothing to assist a cylinder to fill with air. Since the piston moves downward into the crankcase (which let's assume is pretty much at atmospheric pressure) and it's pulling a vacuum to draw air into the cylinder from the manifold which is itself less than atmospheric pressure, the pressure differential multiplied by the cylinder area produces a counter-rotational force. This force is what is called "pumping losses."
You are correct, increasing manifold pressure reduces pumping losses. Running at high engine load (near WOT) is a means of increasing manifold pressure. Boosting, EGR, or throttle-less operation increase manifold pressure (relative to a throttled engine)
Intake turbulence only matters if you have a wet intake (as in a carburetor or a throttle-body injection system) if it even matters then. You want to increase flow turbulence once the intake air has cleared the intake port and is in the cylinder and high port flow velocity does this, which BMW's valvetronic does by limiting intake valve lift.