The terms “balls to the wall” “big brass balls”, and “balls out” have a lot to do with engines and nothing to do with mens’ anatomy.
On a recent harbor cruise mixing automakers and automotive media, our chow line happened to run past what looked to me like a centrifugal governor. It was actually a vintage navigational tool, but in that line I discovered that many automotive insiders didn’t know the original source of the two expressions “Balls to the wall” and “Balls out.” It was by luck that I learned what these terms meant back when I was in engineering school and took a tour of an old museum near the University of Lowell campus.
Both expressions have to do with centrifugal governors used all the way back to the days of steam engines. Rotating machinery needed a way to regulate the engine’s speed. A simple way to do this is to spin two balls off the engine’s drive shaft. These are connected by a rod or a wire to a fuel valve. As the balls spin outward with the engine’s increasing speed, they tug on the wire which acts to close the fuel valve. Thus, the fuel is managed, the machine slows down and the balls droop. The machine reaches a steady-state at its pre-set running speed.
Jay Leno owns a steam engine that has the centrifugal governor front and center and his video here explains it visually. One part not shown by Jay is the “wall.” In some machines the rotating balls are more like rollers surrounded by a cylinder, or “wall” that acts as the regulator. The balls contact the walls of the cylinder at their top speed. Thus, the balls’ contact with the wall can be the machine’s signal to slow the fuel delivery rate. So when the “Balls are to the wall” the machine is at its top operating speed and power. The bottom image courtesy of reddryder and Youtube shows this configuration. The “balls” are actually inside the flywheel, which is cool because it combines two parts into one.
The term “…must have a set of big brass balls” may also be related to this general theme. Since the balls in a governor are not subject to corrosion, they can be made of cheap and heavy iron or steel. However, some fancy machines would use brass just to make the machine more decorative. Being lighter than iron, the brass balls would need to be bigger. So, translating the expression, it means that someone is acting fancier or more showy than they need to.
The next time you are in mixed company and you need to find a phrase that explains all-out running, feel free to lob “Balls-out” or “Balls to the walls” into the conversation. If your guests have a dirty mind, that’s not your fault.