At 08:57 PM 9/9/01 -0700, you wrote:
>Well, I have an important decision to make.
>
>Previously, I had 30" tires and 4.10 gearing in the rear. Now that I'm
>running Hotchkis, with 27.8" tires (275/50R17) I'll be getting at best
>13.5-14MPG with about 80% highway driving. (70/80MPH). I'm to the point of
>not being able to stomach the mileage any more. I could slow down, yes, but
>in California if ya do that, you're going to get run over!
>
>So, should I go back to the original 3.55's, or run 3.92's? I have a 4.7L,
>with QuickD intake, 2x2.25" exhaust, Hotchkis. Future mods: PCM by Mike
>Leech, Flometrics TB & intake that goes with the TB.
>
>I appreciate your help!
>William
If your original OEM tires were 255/65x15s, there is not that much difference
in overall diameter from the 275/50x17s (28.05" vs 27.83" according to the DML
calculator). Your speedo error is less than 1% on the high side.
A 3.55 ratio would be an effective gear ratio of about 3.58 with your
17"ers and
a 3.92 ratio would be an effective gear ratio of about 3.95. You are now
running with an effective gear ratio of 4.13 with your 4.10 and 17"ers.
Going to Carlisle from Burlington, I averaged about 20-21 mpg with 3.55 and
about 19-20 with the 3.92s at about 65 mph on the modded 5.2L. I guess the
choice is between a little mpg loss vs a little more acceleration
performance gain
with the 3.92s. The 3.55 should give you about the same mpg as you had
when you had the 3.55 gears and stock tires.
I doubt very much you'll be able to improve mpg very much seeing as you have
to do 70/80 mph most of the time. HTH.
Bob Tom Burlington, Ont., Canada
'97 Dakota Sport, 4x2, CC, Flame red, 5.2L, auto., 3.92SG
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