[jcus]

The dual 4-71's were connected to a 3 speed transmission that had a 2 spd clutch -- 6 fwd speeds & 2 reverse. The engines also had 2 speed settings for the engine governor, a higher speed for the lower gears & a micro switch to engage the lower speed when in 6th gear.
There are stories about how the drivers would pull the shifter back a little to leave it in the higher speed setting - this would allow the coach to exceed 100 mph.

I am lucky enough to have a friend who remembers working on the twin 4-71's as a greyhound mechanic. The stories he has. . . . .

There were tough in those days [50's] had a 4905, a newer version of the 4501, with a 8-71, once hit 95 by gps going downhill, 2400 rpm. Good name. 'Screaming jimmies' ha!