Jerry,
Nope, different series....80's or 88's are the big dogs...
For comparison: (using the 16x0 series as a base)
1640 = 24" rotor, 436 NA engine, +/- 145bu tank
1660 - 24" rotor, 436 DT engine (turbo), +/-165 bu tank
1680 = 30" rotor, 466 DT engine, +/-185 bu tank.
40 is a nice match for a 6 row head or 20' platform, but no speed demon or powerhouse.
60 will walk a 6 row head (and handle an 8) and cut nicely a 20'-25' platform
80 will walk an 8 row head and cut nicely with a 25' or 30' platform
There is a big difference in the threshing/separating capacity between the 24" and 30" rotors, and a noticeable power difference between all 3 models.....in real good corn that's wet the 40 will really "want" for a turbo
BTW, the numbering series goes like this
1420, 1440, 1460, 1480
1620??, 1640, 1660, 1680
1644, 1666, 1688
2144, 2166, 2188
2344, 2366, 2388
And then the new 8000 series BIG DOGS.