New Gears and WORSE MPG - Ford Powerstroke Diesel Forum
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post #1 of 17 Old 12-29-2012, 04:27 PM Thread Starter
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New Gears and WORSE MPG

I have a 02 7.3 and recently changed the 3.73 gears to 4.88. The truck has a 8" lift and 37" tires. There's a 4" MBRP exhaust and air raid intake and throttle body spacer. Before the gear change I was getting about 11 MPG and now I'm at 8.5 MPG. Any idea's on what the problem is since I was told it would help my MPG's.
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post #2 of 17 Old 12-29-2012, 05:00 PM
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Originally Posted by Waterman View Post
I have a 02 7.3 and recently changed the 3.73 gears to 4.88. The truck has a 8" lift and 37" tires. There's a 4" MBRP exhaust and air raid intake and throttle body spacer. Before the gear change I was getting about 11 MPG and now I'm at 8.5 MPG. Any idea's on what the problem is since I was told it would help my MPG's.
Whoever told you going to a 4.88 would improve mileage lied. Most times you go to a lower gearing, its going to hurt mileage.

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post #3 of 17 Old 12-29-2012, 05:07 PM
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4.88 for rockcrawlin, 37" tire 4.10 is all i would go. motor must be screamin at highway speeds



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post #4 of 17 Old 12-29-2012, 05:15 PM Thread Starter
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My goal was to bring the truck as close to stock performance as I could while keeping the 37's and then build up power from there. What should they have told me to go to for that goal.
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post #5 of 17 Old 12-29-2012, 05:19 PM
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oh how cruel hope that wasn`t a friend with that info for ya

2010 F350 lariat cc sb srw
H&S Black Maxx,S&B CAI,,Readylift leveling kit,,GY 325/60/20,Smoked Recon: tail lights,cab lights,3rd brake light and tow mirror lights,AVS smoked window vents,20% window tints,Curt front mount hitch,Rear hitch mounted lights,Sinister coolant filter,PMF dual steering stabilizer,PMF traction bars 51 Gal. Titan tank,Bilstein 5100`s,Rudy`s up pipes,ARP studs,RCD egr delete w/ elbow,AFE cold side pipe,AFE 4"dp, AFE 5"
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post #6 of 17 Old 12-29-2012, 05:34 PM Thread Starter
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It's what the shop reccomended that did the job. Another shop told me that I should go with 4.56's but I trusted the first shop since they had a great reputation for building rigs.
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post #7 of 17 Old 12-29-2012, 06:29 PM
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Is that hand calculated? I prob would have done 4.10 unless you tow

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post #8 of 17 Old 12-29-2012, 06:31 PM Thread Starter
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I'm not sure what you mean by hand calculated. As far as towing, I don't do a ton of towing but I do pull trailers on occasion.
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post #9 of 17 Old 12-29-2012, 08:49 PM
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37" tires with 4.30 gears would be about the same as stock tires with 3.73 gears. 4.88 is insane unless your towing really heavy or always off the pavement.

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post #10 of 17 Old 12-29-2012, 09:12 PM Thread Starter
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Thanks for that one JSchuricht. I'll look into getting those changed out for that.
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