It is a phrase that lots of gearheads use frequently and probably few know the origin of. When you’re yapping with buddies and tell them that you’re going to run your car, “balls out” or “balls to the wall” you mean that the car will get run full on, to the floor, with everything she’s got. It sounds dirty and inappropriate as hell, but here’s the thing. It isn’t. You’re actually referencing a steam engine when you say that.

James Watt, one of the pioneers of steam engine development in the early 1800s invented lots of stuff. One item was the “fly ball regulator” which worked to regulate steam pressure and speed in a steam engine. As pictured below, the regulator used two balls mounted on arms. These were usually made of iron or brass and depending on the size of the engine they were used on, varied in weight and other details. They all worked the same though.

The regulator was hooked to the flywheel and as the flywheel spun, so did the regulator. As it spun faster the centrifugal force would cause the balls to raise higher and higher until the engine reached full speed at which point the balls would be “out” and facing toward the wall. At this point, the regulator would vent steam to keep the engine from running away or experiencing an explosion due to too much pressure.

As gearheads you know we make up saying and expressions to describe stuff all the time, so when these regulators became virtually standard and chief engineers asked mechanics at what speed an engine was running, they’d reply, “balls out” or “balls to the wall” to indicate it was humming along at full steam.

You’ll still never be able to utter the phrase at church, but the next time one of your bench racing pals says it, ask if he knows what it means and where it came from. Chances are he doesn’t!