I heard that Fearless Frank Fargo got one of these up to near 70 out past Verde Junction.

5 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 00:40:49.831 in the DVD version of the movie.

Quote context

[...]

- All right, all right, all right. Just let's think this thing through logically.

- We know it won't run under its own power. We know we can't pull it. But if we could figure out a way to push it up to 88 miles an hour. Huh?

(STEAM TRAIN PASSING IN THE DISTANCE)

- That's it.

- How fast can she go? Why, I've had her up to 55 myself.

- I heard that Fearless Frank Fargo got one of these up to near 70 out past Verde Junction.

- Do you think it's possible to get it up to 90?

- 90? Tarnation, son, who'd ever need to be in such a hurry?

- Oh, it's just a little bet he and I have, that's all.

- Theoretically speaking, could it be done?

[...]