Regear 3.55 or 3.31 - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 6 (permalink) Old 08-27-2014, 01:33 AM Thread Starter
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Regear 3.55 or 3.31

I acquired this 05 and I'm thinking of regearing. I was planning on regearing the 7.3 but if we sell the 7.3 then it will be the 05 to be done. I see threads about going taller but I'm not towing and I'm not running big tires.

Does this thing produce enough torque to comfortably push 3.55 or 3.31's at 1800-2000 rpms/highway speeds? I know what is possible w/ the 7.3 but I'm new to the 6.0.

"New" 05 no payment, all original 305k and runs like a champ
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post #2 of 6 (permalink) Old 08-28-2014, 05:22 PM
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Re: Regear 3.55 or 3.31

I run 3.08 gears (no longer available I'm afraid) and two stages of overdrive (the 0.78:1 in the ZF6-650 and the 0.8:1 in the Gear Vendor overdrive) resulting in an overall ratio of 1,.92:1 between the flywheel and the tires.

I run OEM-sized rubber (235-85x16). Engine is more or less stock.

At 70 MPH I'm turning 1325 RPM and the engine handles it just fine. At about 50 MPH its on the ragged edge of a lug.

3.31s ought to work just fine. That would give you 1775 [email protected] MPH.

Always a question with changing gearing is: Automatic or stick? With a stick, it doesn't matter but slower down your TC too much could result in spectacular automatic transmissions failures. Parts scattered down the road. Been there. Done that. Paid the bills. Check with your automatic tranny guy of choice.

The 444 Powerstroke has vast low-end torque and will handle it just fine. and get better MPG doing it.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #3 of 6 (permalink) Old 09-10-2014, 05:30 PM
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Re: Regear 3.55 or 3.31

I put 3.31 gears in my Y2K PSDX last year (302K mi). A year and 26K miles later and everything is good. Commuting mileage is about the same, but continuous Interstate mileage improved 1.5 to 2. Engine turns 1700 at 70 MPH, which means you don't get to the dreaded 2000 until 85. EGT is a tad higher. I have single shot injectors and Beans' tunes so acceleration is not an issue.
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post #4 of 6 (permalink) Old 09-10-2014, 08:17 PM
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Re: Regear 3.55 or 3.31

6.0 hates life below 1600...... Doesn't get happy till 1800.

06' F250 Harley Davidson Edition(Factory 2.5" lift)CCSB-blue sping kit, ARP, gaskets up, Driven Diesel Coolant Return, Sinister Diesel Coolant filter, Rotella ELC, SCT X4, 55gal Aluminum Fuel tank, B & W turnover. ...Hauling New RV's daily.
02' F250 687,000 miles towing...traded to friend for a boat
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post #5 of 6 (permalink) Old 09-11-2014, 05:07 PM
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Re: Regear 3.55 or 3.31

I suppose "...hates life..." is in how you look at it.

For almost all turbocharged diesels the lowest brake specific fuel consumption (lb/HP-hr) "island" is generally in the "high load - low RPM" part of the performance envelope. In short, just at the ragged edge of a "lug". There's no free lunch, you make a gain, you give something up.

At 70 MPH/1325 RPM, I can feel just a hint of torsional vibration. At 45 MPH/850 RPM , it's time to downshift.

But the more of that vibration I can feel, the better my MPG gets.

But for an aerodynamic nightmare like a pickup pulling an RV and the lack of torque/RPM control that my manual transmission gives me, I'd say the load is so high that 1600 RPM at highway speed you are probably into a lug.

Load matters - and that's why pickups are the most challenging vehicle to wring good MPG out of.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #6 of 6 (permalink) Old 09-17-2014, 10:56 AM
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Re: Regear 3.55 or 3.31

I have a 3.55 with the E4OD in my 96 7.3 used for towing a 28-foot travel trailer. My total rig is at 15000 pounds, which I believe Ford specified as maximum GVWR with that axle.

My normal towing speed is 55mph at about 1450 rpm in fourth gear (O/D). At this speed, I average about 14mpg.
Not towing, at 70mph I average 21mpg.

I'm happy with that.
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