Fuel economy

Discussion in 'Trucks [ Eighteen Wheelers ]' started by GCK, Oct 12, 2017.

  1. GCK

    GCK Bobtail Member

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    Jan 18, 2017
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    I'm running a 99 Freightliner Classic with a 500HP Detroit. Super 10 , 373 rears. Averaging about 6 mpg. Is that about what I should expect or are others doing better. All info appreciated. Thanks
     
  2. uncleal13

    uncleal13 Road Train Member

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    I had a 2001 Classic with a 565hp ISX. It got 5.88 mpg, so yours sounds right to me.
    Certainly can get better on some days, but the wind kicked the heck out of it.
     
  3. benjamin260_6

    benjamin260_6 Light Load Member

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    Are you happy with 6mpg? With some adjustments to your driving and some upgrades to the truck there's no reason you can't get 7.5+ but it's all in how bad you want it.
     
    KB3MMX Thanks this.
  4. KB3MMX

    KB3MMX Road Train Member

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    Bingo.

    Those trucks are capable of 7.2-7.5 with correct specs and driving.

    Change to a modern VVT turbo , add economy tuning and downspeed the rears(2.85-3.08 range), change to a 13spd and you'll be 8+ capable.
     
    GCK Thanks this.
  5. little cat 500

    little cat 500 Road Train Member

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    that's normal only way your getting better is drive like granny
     
  6. benjamin260_6

    benjamin260_6 Light Load Member

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    That's a $15000-$20000 upgrade and it's not going to get you from 6 to 8mpg. Things like high flow mufflers/air filters, low rolling resistance tires, making aerodynamic improvements like roof fairings are all a lot cheaper and will get a better return on investment. Things like re-gearing, transmission swapping, and variable vain turbos are things you do when you're already getting 8mpg and want that little extra when you're already changing those parts
     
    gokiddogo Thanks this.
  7. Luwi67

    Luwi67 Medium Load Member

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    Oct 24, 2012
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    I have a long nose Pete, Cat 550, 13 spd, 3.73 and 24.5 rubber. Zero aero mods, pulling a dropdeck and average 6.8. I rarely see lower than 6.6 and see 7 to 7.2 often.

    Only thing I do is keep the rpm at 1350-1400 at cruise, tach never sees over 1600 when shifting and I try to keep my boost gauge as low as I can on hills. I also noticed the boost gauge will rise when using the jake on downhills so I only use it when I'm heavy.
     
  8. benjamin260_6

    benjamin260_6 Light Load Member

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    Just FYI you're Truck isn't using any fuel when the Jake's are on. The Jake's only open the exhaust valve at the top of the compression stroke. That exiting exhaust is spinning the turbo and causing the boost pressure.
     
    BoostedTeg and uncleal13 Thank this.
  9. Luwi67

    Luwi67 Medium Load Member

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    I had wondered about that, makes sense now.
     
  10. GCK

    GCK Bobtail Member

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    Jan 18, 2017
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    Thanks everyone.
     
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