Thread: rpm reducing
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Old 01-29-2016, 02:37 PM   #7 (permalink)
elhigh
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Join Date: Jan 2008
Location: SE USA - East Tennessee
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Josie - '87 Toyota Pickup
90 day: 27.96 mpg (US)

Felicia - '09 Toyota Prius Base
90 day: 53.29 mpg (US)
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Standard tire size = 195/75 R14
790 revs. per mile

Truck's rear = 3.73:1
W56 5th = 0.85:1


Overall top gear ratio = 3.17:1
engine revs = 2507

With 3.55:1 rear = 3.02

= 5% rpm reduction
engine revs = 2385

With 3.35 rear = 2.85

= 10% reduction
engine revs = 2251

The 22R isn't really powerful but makes good torque for its power, and makes it pretty low in the rev range. It's a super flexible, meaty engine down low if you don't ask too much of it. Puttering along at 50 in top feels great, 60 feels thrashy. Having 3.35 gears would move my cruising speed down into less buzzy territory.

As to what that would do to my MPG, I can only speculate. It's carbureted. I can only record tank-to-tank, there's no instant display that really helps. Even the vacuum gauge isn't much use, it keeps wandering up to where it shows 10" when the engine is off. But I know that this is a pretty light truck, I never drive very fast and rarely have a large load (firewood once in a while, the wood splitter once in a while, Lowe's once in a while). I've had it since it was new.

ROI = never. There is no such thing on a truck this old, there's just wrenching because it's more interesting than watching TV.
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