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Surprising MPG results with 4.10 gears

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Old 05-26-2015, 08:07 PM
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Car: 1991 Z28
Engine: 5.7 TPI L98
Transmission: 700-R4
Axle/Gears: Moser 9" with 4.11
Surprising MPG results with 4.10 gears

Here is the powertrain: Moser 9" with 4.10's and locker diff, 700R4 with a shift kit, bolt on L98 (est 300hp). 18" wheels (25 1/2" tire). Car is 200 lbs lighter than stock.

The speedo is off and the odometer counts wrong. I used my GPS on my trip today. I topped off the tank before and after. I drove 80 miles (70miles highway 10 miles city). Set the cruise @60mph RPM @2250.

I used 3.75 gallons = 21.33 mpg!?

Maybe that's normal? I was estimating 16
Old 05-27-2015, 06:16 AM
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Car: 1985 Trans Am T-Top
Engine: 305 TPI
Transmission: T-5 5 Speed
Axle/Gears: 3.42 posi 1LE 10 bolt
Re: Surprising MPG results with 4.10 gears

There's a margin of error in topping off, doesn't always shut off at the same point. Need to measure after using a larger amount of gas to minimize the margin of error. At least a full tank.
Old 05-27-2015, 11:25 AM
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Join Date: Feb 2004
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Car: 1991 Z28
Engine: 5.7 TPI L98
Transmission: 700-R4
Axle/Gears: Moser 9" with 4.11
Re: Surprising MPG results with 4.10 gears

I was thinking that. I think I had gas up the filler neck on the first top off. I may never know because this car never gets filled past half tank until yesterday haha.
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