Doc: [into the walkie-talkie from inside the cab of the train] Each detonation will be accompanied by a sudden burst of acceleration. Hopefully, we'll hit 88 mph, before the needle gets much past 2,000.
Marty McFly: [into the walkie-talkie] Why, what-what happens after it hits 2,000?
Doc: [into the walkie-talkie] The whole boiler explodes.
Marty McFly: Perfect!