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Discussion Starter #1
Given: 4bta in a cj7 3:21 gears 700r4 trans 31inch tires.
i'm getting a around 17mpgs around town and 20? highway.
need to know if this is it....
later
 

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That sounds low to me. My Carryall is 7300 pounds curb weight and loaded for my trip considerable more which included (4) 5 gallon Gerrys cans of D'zl, spare parts and tools. I am running a 4BTA (CPL 857) into a NV-4500/NP-205 turning 4.89 ring and pinions and 36" tires. My fuel use on a 3411 mile trip was 25.9115 mpg. This included 539 miles of primitave gravel road running for hours in lower gears at 20 MPH due to terrible condition of the road. Had I been on good black top for the entire trip, I would have been close to 30 mpg. I ran legal road speeds which typically were in the 50 to 60 mph range.

Paul
 

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Have any fuel rates, timing, etc been changed?
 

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Discussion Starter #4
it is a rebuilt 4bta...
no mods...
3 inch exhaust...
timming ?
i wouldn't know how?
mabey its off from the rebuild?
 

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1989 Jeep Wagoneer, 360v8, 727, stock for now,
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I average 23 in town in my 4300 lb Scout 5 speed.
 

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1989 Jeep Wagoneer, 360v8, 727, stock for now,
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what gears are you running and what rpm at cruising speed?
3.73 gears, 33x10.50 BFG mud, NV4500
About 1864rpm @ 65mph, 2004rpm @ 70mph
 

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Discussion Starter #9
i just picked up a multimeter that reads rpms....
it was about $60 but you can get cheaper ones...
it read about 650rpms on idle
in gear it read 600rpms
25 mph it read 1200-1300rpms
40mph it read 1400rpms
55mph it read 1500-1550rpm in overdrive
dose this sound about right???
i have the alternator with the pickup terminal.
jbox
 

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Feed your data into this calculator then compare. You can use the mileage markers on the highway to check for speedo error. Once you know the correct answer from this calculator you can double-check tachometer readout for accuracy.

http://www.4lo.com/calc/gearratio.htm

JimmieD
 

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Ha ha, lots o guys use them to check the accuracy of their vehicle speedo! I suppose there's good GPS and bad ones, so a qualified 'Yes', if it's a decent GPS.
 

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If your GPS displays your position, it has acquired the needed satellites. That being the case, its deadly accurate, given your GPS is working properly. Have no fear, you will not drive faster than the GPS can calculate ha ha

Paul
 

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Your Garmin will be fine. I would trust it for accuracy over any speedo in a vehicle. So you may see a small difference, trust the GPS.

Paul
 
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