Wiktionary
n. (context idiomatic English) Amount of energy.
Wikipedia
Head of Steam, formerly known as the Darlington Railway Centre and Museum, is a railway museum that is located on the 1825 route of the Stockton and Darlington Railway, which was the world's first steam-powered passenger railway. It is based inside the station building at the North Road railway station. Its exhibits are devoted to the area formerly served by the North Eastern Railway with a particular focus on the Stockton & Darlington Railway and the railway industry of Darlington.
Usage examples of "head of steam".
It took a kilometer or so, but it was getting up a head of steam when it reached the wall.
Little by little the tidal stream slackened, the close-locked floes fell slightly apart, and under her full head of steam the ship began to forge ahead towards the open sea and safety.
They had the booty on board before Tadaos could get a head of steam up.
Let's see if we've got sufficient head of steam to move the engines.
Although started with a good head of steam, the Sea Dragon got even faster by the moment, as if propelled by the anger and resentment of the old baron.
Seas were under two meters, and she was under a full head of steam heading north-northwest, great clouds of gray-white steam leaving a kilometer-long double line from her twin stacks.
And on that Friday evening, we appeared to have a full head of steam, and the way ahead looked good and clear.
The engineman on the boat had brains enough to have a head of steam up, and we had no choice but to push off and look for help.
She would go sit with them, but Di had a head of steam he was willing to let off, which would have his blood pressure up telling her the tale.
The Prince was building up a head of steam, as he often did when the subject of Ix came up.