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Old 02-08-2012, 12:51 PM
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Originally Posted by Msgt
Sorry to bother you..but my question is on your gear ratio of 3.27 with a 700r4. You said you were getting 20 mpg with it. I read that the best mpg is had by keeping your rpm between 2000 and 2200. Now i drive a 70 mph and my calculations came out to a rearend from 3.48 to 3.80. So with a 3.27 did it feel doggy at highway speeds and what speed do you drive. Im curious if i calculated wrong. ie 3.48 @70mph came t0 2010 rpm. If you feel you could go with a higher rearend it would help on gas and i would sure be interested in that.I have never had a 700r4 so im in the dark here, but I dont want to be lugging the engine down by going to far on the high side. Let me know what you think. And i would like to know what mph your at when you hit 2000 rpm in overdrive..Thanks
msgt pm'ed me, i figured i'd answer in this thread to bring it back to life

a lot depends power vs weight, the ramjet 350 i installed has 350 hp and 400 ftlb and these trucks are light.
my 09 sierra cruises 70 mph at 1800 rpm and gets 19 doing so.
my 58 truk does not have a tach, but it is a lot lighter than my 09.
driving 75 mph with the cruise on, on I75 thru the kentucky mountains it never downshifted or felt doggy.

being a light truck it is still a tire smoking monster due to the low 1st gear of the 700r4.
under normal acceleration it shifts into 2nd about 30 ft from start.
under hard acceleration, my truk is moving 10 mph when the speedo shows 60 mph
if i was so inclined, i'd go lower with the ratio, maybe as low as 3.00, just to see my mileage and performance.

a previous motor and trans i had in this truck with the stock rearend, we put in my son's elcamino.
while it was a hot motor in my truck, it was a dog in his elco.
we ran the casting numbers that showed it was a 1975, 140 hp motor.
don't over engineer your mileage numbers, these trucks are just very light.

as far as what speed do i drive? usually the speed limit, but i consider the freeway open to interpretation

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