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Figured out the odo/speedo difference. Man, I'm not very swift sometimes (actually I'm part Swift now, but... bad pun, never mind)...
The 5.7% difference has nothing to do with the final drive. Since the speedo cable runs off the FD, it *should* show the same vehicle speed on the gauge regardless of FD because the axles/wheels/tires are going to turn the same number of revolutions for a given distance. Only the engine speed changes.
BUT... the Swift the 3.52 FD came from had slightly different sized tires on the end of its axles: 165/65/13's if I remember right. Since I'm running the stock 155/80/13's that came with my original 4.39 FD, I've reduced the RPM of the axles.
As it turns out, the outside diameter difference between the 2 tire sizes results in a calculated 5.8% axle RPM difference. Pretty darned close to the 5.7% difference I saw last night. That's where my odo/speedo error is coming from.
Mystery solved!
Bonus: since my stock tires have a slightly bigger outside diameter than the tires that were spec'd for the 3.52 final drive from the Swift, that means is I'm actually adding to the gearing difference even more than the FD swap alone. Cool!
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