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Old 08-20-2011, 03:07 PM
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Rear end gear ratio suggestions needed

About to ask what I hope isnít a stupid question but if it is then please just bear with me. Iím building a 1954 Chevy Truck (3600) for a daily driver. Most of the driving will be city miles with occasional trips up and down the interstate. Iíve dropped a SBC 350 and 700R4 that I pulled from a donor vehicle (1988 full size Chevy Van). My rear end comes from a 75 Nova and has as best I can tell 2.55:1 gears.
Hereís my question. Considering that Iím not looking for extremely quick acceleration or planning to do any racing and Iím more concerned about gas mileage would any of you suggest that I change the gear ratio? And why or why not?
I apologize if this seems like a truly silly question but considering this is my first build and I donít have a lot of knowledge I wanted to ask.

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Old 08-20-2011, 07:40 PM
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drive it

best way to tell is to drive it.

my 65 chevelle had a 2OOR4 and a 350 motor, running 27" tires and a 3:O8 gear, the motor rurned 21OO RPM at 6O MPH. l have been told that if the RPM gets below 19OO at speed, vibrations and other things can happen.


later
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Old 08-21-2011, 08:10 AM
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If you have something close to stock tire size for a truck (i.e., a 245/75R16 in modern sizes) it would be about 31" in diameter. When combined with a 700r4 and 2.55 gears you have a really high overall gear ratio. Use this site to make some comparisons http://www.grimmjeeper.com/gears.html .

I think you would want more like 4.11's, or perhaps 3.73's if you have stock height tires. With 4.11's and 31" tires you would be at about 2200 RPM when cruising at 70 mph in OD. 3.73's would drop it down to about 2000 rpm cruise at 70 mph. Unless you have built a real stump-puller engine, I would want to keep it in that power range.

Bruce
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Old 08-21-2011, 09:13 PM
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two more

http://project33.com/tiresize.cfm

http://www.florida4x4.com/tech/gearcalc.php

on the 4x4 site put 1.1 where it asks for tranfer case.

Later
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Old 08-21-2011, 10:03 PM
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3:50 or 3:73 would be ideal for the 700R4 and the tire size you would be running. The original 2:55 gear combined with the 700R4 overdrive of .7 and tall tires will put your engine in a lugging condition at highway speeds which will wreck your gas mileage.

Vince
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