Actually, there are both 4.11 and 4.10 Eaton gears. Earlier stuff is 9/37 4.11:1, and later stuff is 10/41 4.10:1. All SM420 are 1:1 in high gear, as are almost all older light truck/car transmissions. (The input shaft locks to the output shaft; no actual gears being used.)
BTW,
this is another good site (
http://f-body.org/gears/)
If you're using the tire diameter to figure speed, remember that you need the theoretical "loaded diameter" (loaded radius x2). Making a mark on the tire and pavement and rolling it (while it's on the truck) is an easy way to get the "loaded circumference". Then divide the 63,360" in a mile by that, and you have your revolutions per mile figure.
Here's some of my own crap, FWIW:
Engine RPM x 60 / (final drive reduction x tire revolutions per mile) = MPH
MPH x (tire revolutions per mile x final drive ratio) / 60 = RPM
Also; RPM = (mph x trans ratio x gear ratio x 336 ) / effective tire diameter (loaded diameter)
235/85r16 MT @ 645RPM x 4.1 = 2,645 /60= 44RPM @ 1MPH
80@3,525
75@3,300
70@3,075
65@2,875
60@2,650
55@2,425
50@2,200
45@2,000
40@1,775
35@1,550
30@1,325
