Cummins X15 questions.

Discussion in 'Experienced Truckers' Advice' started by Barricadebouncer, Sep 1, 2026.

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  1. Sep 1, 2026 #1
    Barricadebouncer

    Barricadebouncer Light Load Member

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    Considering buying a ‘21 or ‘22 KW T680 with a Cummins X15 efficiency package.

    Assuming that most of them setup that way will have a 3.55 rear end.

    How do they run?

    Average fuel economy?

    How do the run deleted?

    How do they run with the power turned up?

    Any information will be appreciated.

    Thanks in advance.
     
    Barricadebouncer, Sep 1, 2026
    Barricadebouncer, Sep 1, 2026
    #1
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  3. Sep 1, 2026 #2
    me myself and I

    me myself and I Heavy Load Member

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    If it's a auto box it'll likely will have 3.08 rear end
     
    me myself and I, Sep 1, 2026
    me myself and I, Sep 1, 2026
    #2
    Otr Traveler Thanks this.
  4. Sep 2, 2026 #3
    snowwy

    snowwy Road Train Member

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    The 21 579 i ran had 2.64.
     
    snowwy, Sep 2, 2026
    snowwy, Sep 2, 2026
    #3
  5. Sep 2, 2026 #4
    Concorde

    Concorde Road Train Member

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    I don’t associate a 3:55 axle ratio with fuel economy.
     
    Concorde, Sep 2, 2026
    Concorde, Sep 2, 2026
    #4
  7. Sep 2, 2026 #5
    D.Tibbitt

    D.Tibbitt Road Train Member

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    Ive never got better than 6.5 mpg on any cummins. But flatbed only ... Dont turn the power up. can delete it but they have problems with bad deletes..
     
    D.Tibbitt, Sep 2, 2026
    D.Tibbitt, Sep 2, 2026
    #5
    Deere hunter and Diesel Dave Thank this.
  8. Sep 2, 2026 #6
    Diesel Dave

    Diesel Dave Last Few of the OUTLAWS

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    Turn up a Cummins today ? :laughing-guffaw:They’ll grenade before you know it.
     
    Diesel Dave, Sep 2, 2026
    Diesel Dave, Sep 2, 2026
    #6
    D.Tibbitt, Deere hunter and Short Fuse EOD Thank this.
  9. Sep 2, 2026 #7
    Short Fuse EOD

    Short Fuse EOD Road Train Member

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    I wouldn’t turn it up unless you are ready to pay for a dropped liner.
     
    Short Fuse EOD, Sep 2, 2026
    Short Fuse EOD, Sep 2, 2026
    #7
    D.Tibbitt and Diesel Dave Thank this.
  10. Sep 2, 2026 #8
    MACK E-6

    MACK E-6 Moderator Staff Member

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    How about if it was simply neutered by the previous owner and “turning it up” only means restoring it to factory specs?
     
    MACK E-6, Sep 2, 2026
    MACK E-6, Sep 2, 2026
    #8
    Short Fuse EOD, D.Tibbitt and Diesel Dave Thank this.
  11. Sep 3, 2026 #9
    Barricadebouncer

    Barricadebouncer Light Load Member

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    Appreciate all the feedback
     
    Barricadebouncer, Sep 3, 2026
    Barricadebouncer, Sep 3, 2026
    #9
    D.Tibbitt Thanks this.
  12. Sep 3, 2026 #10
    Short Fuse EOD

    Short Fuse EOD Road Train Member

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    Good point.
     
    Short Fuse EOD, Sep 3, 2026
    Short Fuse EOD, Sep 3, 2026
    #10
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