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Racers use vacuum on their crankcases not to decrease pumping losses, but to cut down on the amount of air that must be moved between the backs of the pistons. For a big-block V8 at 6K rpm, this is significant. For us, it's not.
Pumping losses come from the pressure differential between the intake and exhaust. With a shut throttle, your engine is basically an air compressor, compressing the ~2psia intake charge to the 14.7psia atmosphere. With an open throttle, it's simply moving air. There's no net compression going on.
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