Forum Discussion

pcoplin's avatar
pcoplin
Explorer II
Aug 03, 2019

Dually gearing? Coming from a SRW

Sold my 2005 F250 Powerstroke diesel SRW, 3.73 with 285s on it (34s). Gearing felt great, at 2k RPM I was around 74 mph.

This new dually (same year/engine) has 4.10s and 245s (like 31-32 inches). Aside from just being overall lower, the gearing seems super high, 2k RPM is 63 MPH. Feels like I'm in 4th all the time.


Question is, will my fuel mileage suffer cranking along above 2k RPM? I regularly go 70 or more in Utah and Nevada. I know I can go to 255s (33s) but I was thinking of regearing it myself. Worth it?

Thanks!
Truck Campers
  • jimh406's avatar
    jimh406
    Explorer III
    Aug 03, 2019
    I have 4.30s. I think the mpg loss is significant unloaded at anything near 60 or higher. Loaded with heavier load, I think it makes a minor difference.

    Check the prices, but it’s probably worth regearing if you will keep it. For my truck, it’s around 2000 to regear. A F350 will be less, I believe.
  • emcvay's avatar
    emcvay
    Explorer III
    Aug 03, 2019
    My new F350 Dually gave me 10.5mpg on a 1200 mile round trip with the latter half trucking along at 70MPH the vast majority of the time and it has 4.10's. I'm guessing the 6 speed gear box is the reason and perhaps the massive power (hard to imagine it until I drove it fully loaded for a week long trip).

    My 6.4 with 3.55's in comparison only gave me 9mpg in those conditions on the same trip.
  • Kayteg1's avatar
    Kayteg1
    Explorer II
    Aug 03, 2019
    With low gearing (high number) the mpg will suffer, but not by huge number.
    2005 comes with 6l Powerstroke? Good luck with that.
    I had F450 that would run over 2000 rpm all the time and the noisy engine was annoying.
    Now I don't hear 6.7l cruising at 1600rpm at all.
  • Grit_dog's avatar
    Grit_dog
    Navigator
    Aug 03, 2019
    Not goi g to make much difference in mileage IMO. You just bought a truck for towing heavier than your old truck is all. 6.0 won't care. No issues running a little higher in the rpm range.
  • BradW's avatar
    BradW
    Explorer II
    Aug 03, 2019
    Ditto. The 6.0 likes to run at higher rpm. Run it like a 4 cyl Yoter and it will be happy.

    Bradw
  • pcoplin's avatar
    pcoplin
    Explorer II
    Aug 04, 2019
    Thanks all. Right now it's just an annoyance, with a louder engine and more responsive throttle. I'm sure I'll get used to it, and wont be a big deal unless the mileage takes a huge hit.

    Gears are no problem for me to change, and would run 500-600 in parts with new bearings. Certainly cheaper than tires for now.
  • dwrat's avatar
    dwrat
    Explorer
    Aug 05, 2019
    Of course, it will use more fuel.
    Think of it this way.
    At 1600 rpm's your squirting the injectors say 160 times a minute.
    At 2000 rpm's your squirting the injectors say 200 times a minute.
    Every squirt, under the same load, should spray the same amount.
  • pcoplin's avatar
    pcoplin
    Explorer II
    Aug 05, 2019
    dwrat wrote:
    Of course, it will use more fuel.
    Think of it this way.
    At 1600 rpm's your squirting the injectors say 160 times a minute.
    At 2000 rpm's your squirting the injectors say 200 times a minute.
    Every squirt, under the same load, should spray the same amount.


    You would so,but that's not the case. Depends on load, which changes injector pulse width and injector timing, Also depends on torque/horsepower curves of the engine.

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