Where did this term "chunk" come from?

I will have to say I am guilty of this.Way back in younger days.
Home was Pa.School was Denver Colorado. Would swap in 2.94 for the 1600 mile drive.
Swap in 3.91 once at my destination.On the ground. 4 times a year during school breaks.
Being 17-18 never thought twice about it. 70 340 4 speed Duster. Do the tall tire thing too.
Yup those were the days! LOL