Dunno - I thought that Iron Horses were steam engines. BTW, did you know an idling diesel engine has the same rhythm as a purring cat?
“an idling diesel engine has the same rhythm as a purring cat?”
That tidbit seems to be ‘out there’.
Different types of diesel engines, two-stroke cycle, and four-stroke cycle also the number of cylinders.
If my ciphering is correct a 4 cylinder four-stroke idling ~800 RPM would produce 26.6 pulses/sec
And why would it be different than a gasoline engine?
Cats purr for reasons beyond contentment. Newborn kittens are born blind, so a mother cat will purr to orient her kittens toward her at feeding time. Cats also purr when they are sick or even in the process of dying as a self-calming technique. Cats purr at the same frequency as an idling diesel engine, about 26 cycles per second.