We often hear tell here of the Wärtsilä RT flex 96C, because it was (sadly it’s obsolete) the biggest piston engine in the world. It was an engine of superlatives, with up to 14 cylinders (yes, an I14 is a thing) with 1,820 litres per cylinder and 107,000 bhp which corresponds to very few hp per litre. Then again it could produce 5.6 million torques and had a thermal efficiency of just over 50% which makes the average car engine look silly.
It’s called a “cathedral” engine because it’s built like one with a weight of about 2,300 tonnes, or if you prefer 2,260 tons or if you further prefer 2,535 little American tons.
However it’s not all big numbers.
During development Wärtsilä found that they could persuade the 12 cylinder model to run at 7 rpm. Yes, the crankshaft would turn once every nine seconds or so which is something like those steam engines they had in the 19th century.