Does the torque rating really effect mpg?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by GTOVR4, Jun 21, 2016.

  1. bavarian

    bavarian Heavy Load Member

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    X1Heavy: Amen
    Well said.
    Derating an engine never did any good. On a post 2010 engine you're going to ask for trouble. Aftertreatment might not get up to temp when needed, causing failed regens and so on.
    IMO you're better off in the long run with the original setting. Swallow the higher insurance premium if you really need it but you will save on down time and loss of income.
     
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  3. Ristow

    Ristow Road Train Member

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    you lose 25 hp and keep the torque,and get a cheaper warranty? i'd go with the 475 horse. the more warranty the better,especially with all the problems the epa era motors are having.

    you won't notice the 25 hp difference.
     
    mp4694330 Thanks this.
  4. KeithT1967

    KeithT1967 Road Train Member

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    Torque "rating" doesn't effect anything at all. Torque "applied" effects everything.

    Torque is an actual measurement while HP is a calculation. The formula is (Tq x RPM)/5252 = HP

    If you look at a dyno plot of a gas engine you can see the Torque and hp lines cross at 5252. Every single time.

    When a big diesel is detuned in HP but the peak torque rating is unchanged all they are doing is limiting fuel at the top of the rpm band. Cummins does this above 1500 rpm on the ISX 15's.

    Yes the higher HP engine can cross the mountain faster but to do it you'd have to be flogging the engine. Plus using that extra 25hp means more fuel consumption, more heat, and more stress on everything in the driveline.

    Pick the right gear and there isn't a bit of difference in how a 500/1850 and a 475/1850 will climb. Nor is there any difference in the fuel consumption. Fuel consumption is gear selection and your right foot. You can get a 600hp/2200lbft fire truck tune (yes, there is such a factory tune for several Cummins) to sip fuel, and you can make a 435/1650 guzzle like a Detroit 8V92.
     
  5. GTOVR4

    GTOVR4 Bobtail Member

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    Thanks for the input guys

    I will want extended warranty for sure.

    With 2 more year and 300k miles extra it's worth it for $5200 and its inculed after treatment.....
    (Total 4 years 500k miles .

    I am not too worry about the 25 hp diffeence which I won't need that horsepower anyway

    So sounds like bigger torque rating will not burn more fuel if I drive it right?

    I wonder why those smaller block engine like D13 and MX13 limited the torque rating at 1650
     
  6. Ristow

    Ristow Road Train Member

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    turning an engine up is a lot harder on it and the rest of the truck than derating it. derating hurts nothing.
     
  7. Sportster2000

    Sportster2000 Road Train Member

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    To tell you honestly you are never going to notice that 25 horsepower not being there. Drive it easy and no drag racing from stop lights and you should get decent fuel mileage.
     
  8. NWAF

    NWAF Light Load Member

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    My buddy got an isx 475/1650 i have 525/1850 and i get better fuel avg at 80 gross driving back to back from WA to MO. Both trucks 342 ratio 13 spd manual. Only difference is i have volvo he has cascadia, both have good aerodynamics. But i do believe in slower speed and flat ground the 475/1650 would consume less fuel, but on hills he has to downshift 1-2 gears more than me and thats killing his avg. Torque does kill fuel mileage.
     
  9. x1Heavy

    x1Heavy Road Train Member

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    No torque does not kill fuel mileage. Constant over head past horsepower will killl
     
  10. allan5oh

    allan5oh Road Train Member

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    Torque and horsepower ratings have nothing to do with engine thermal efficiency (BSFC). However higher ratings make it easier to waste fuel. For example going full throttle up a hill not losing speed, only to crest the hill and get on the other side with your brakes. A good driver would back off before the crest and use the other side to get back up to speed. A gutless engine wouldn't have a choice.
     
    Last edited: Jul 7, 2016
  11. gokiddogo

    gokiddogo Road Train Member

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    Best thing you can do is learn to drive with a boost gauge .... watch and see how if you mash it up the hill at max boost versus keeping a constant say 20-25 psi you only give up a few mph but you don't work the engine nearly as hard ... try to keep it under 10 while cruising on the flat land. Higher boost always = lower mpg. Cruise is your enemy sometimes.
     
    KeithT1967 and spyder7723 Thank this.
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