These three in the furnace will ignite sequentially, make the fire burn hotter, kick up the boiler pressure, and make the train go faster.
7 seconds sound clip from the Back to the Future Part III movie soundboard.
You can hear this line at 01:34:09.694 in the DVD version of the movie.
Quote context
[...]
(STEAM TRAIN BRAKES SCREECHING) (2)
- Uncouple the cars from the tender!
(STEAM TRAIN WHISTLE BLOWING) (2)
- I've wanted to do that all my life.
- What are these things, anyway?
- Marty, are the time circuits on?
- Input the destination time. October 27, 1985, 11:00 a.m.
- Check.
- Okay, we're cruising at a steady 25 miles an hour, Doc.
- I'm throwing in the Pres-to-Logs.
[...]