By the way, forcibly moderating the speed by grasping the governor was referred to in Victorian times (not making this up) as "cupping the governor's balls" which was one of those "plausible deniability" phrases (it was literally true so if someone objected they were the ones with the dirty mind).

But those people knew that they were being risque, right?

I’m sure, yes.

Ahahah, came here to mention this. You beat me to it! Also called "balls to the wall".

Balls to the wall has a different etymology. It implies pushing a throttle lever all the way forward. An airplane version of “pedal to the metal”.

“Balls out” and “balls to the wall” are two different technological metaphors with the same general idea though (going at top speed).

I had a very different assumption of where those phrases came from until now