help with rpms

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Jan 8, 2013 | 12:30 PM

1989_f250

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help with rpms

i just put a 6.9 in my f350, it originally had a gasser so i have no tach, it has a 4 speed with 3.55s about what kind of rpms at 60 mph and what kind of fuel mileage am i looking at?

Jan 9, 2013 | 04:58 AM

LittleRedRanger4.0

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From: Croswell, MI

at 55 mph about 2300 rpm and at 60 mph prolly 2500 rpm. i get 14-18mpg

Jan 9, 2013 | 05:35 AM

Ford F834

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From: Northern Arizona

If you are running stock 235/85/16's (calculated at 31" diameter) tires, with 3.55 axle gears, in 4th (1:1) your rpms will be:

35 mph = 1,374
40 mph = 1,540
45 mph = 1,732
50 mph = 1,925
55 mph = 2,117
60 mph = 2,310
65 mph = 2,502
70 mph = 2,694
75 mph = 2,887
80 mph = 3,079