balls to the wall

To go at full (unregulated) power

Steam engines had mechanical regulators that consisted of a pair of hinged lever arms with a ball on the end of each arm, as the engine sped up the centrifugal force caused the arms to raise up closing a valve. If you adjust the regulator so that the arms go to horizontal (with the balls pointing to the wall) without closing the valve you are not limiting the speed of the engine.

When the captain called for balls to the wall, we stoked the fire and pushed the throttle to full.

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