> -----Original Message-----
> so is the 3.90 rear good for acceleration (track)? what rear diff
> would be better suited for the track?
> and does the change in rear make the truck not good a daily driver?
> =====
> Dan K.
Dan, the 3.90 is very nice for the street and track with a stock or mildly
modded engine. As you have noticed, you can change the "effective" gear
ratio with tire diameter. For best acceleration, the numerically higher
gear ratio is better (but referred to as a lower gear ratio). I was
running high 13's at the track with my 3.90 gear and 26" dia tires. I
switched to a 4.30 gear with a 28" dia tire to put a larger "footprint" on
the track for more consistent traction. The "effective" gear ratio resulted
in basically the same as I had before with the 3.90/26" combo. Cruising
rpm went up about 100 at 70 mph and I saw no difference in gas mileage.
(was still 21 mpg until I went with the Hughes cam and M1 intake, now just
above 20 mpg) Another example...if I were to switch back to 26" dia tires
with my 4.30 gear I'd have an "effective" ratio of about 4.56 and I would be
a little quicker in the quarter mile (assuming I had traction).
RayB
http://www.dragtruk.com/ENTRIES/20KM1FD2KWBP.html
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