Quote:
Originally Posted by 66birdman
I guess I must be lucky or something. I have a 66 C15 with a completely stock 351E, SM420 and Dana 60 with either 4.11s or 4.56s (havent dug that far into it yet) and I get around 14mpg cruising at 55ish. Not sure what my RPMs are since I dont have a tach but I did put slightly oversized tires (235/85/R16) on it to make it capible of highway speeds. Side note the vintage salvage yard here where I live has a 4 speed with an aftermarket overdrive still attached to a 65 GMC if anybody wants me to go ask about it. I dont remember if the tranny was a SM420 or a SM465 though.
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At 55mph with that tire size 4.56s=2658rpms
4.10s= 2390
3.54s=2063
To get that good of mileage I'm guessing someone might have changed your years already.
My best friend owns a gear shop and he told me that 3:31s are available for the DANA 60. He looked it up right in front of me but he might have made a mistake...