Cummins isx pulling rpm

Discussion in 'Ask An Owner Operator' started by Massey1100, Feb 7, 2023.

  1. Massey1100

    Massey1100 Bobtail Member

    Feb 7, 2023
    Just purchased a 2012 international Lonestar equipped with a deleted Cummins isx 450, 18 speed eaton, 3.73 rear end with 22.5 tires. So far love the truck. Comfy, and a joy to drive, haven’t got a whole bunch of time behind the wheel of this truck yet. I am just wondering what the best rpm to pull at is, I pull a grain trailer, gross weight would be 46 tonne or about 100,000lbs loaded for primary winter weights in SK Canada. Pull flat land with some rolling hills. 65mph I sit about 1700 in 17th or 1450 in 18th. It seems to pull just fine in either gear, and fuel economy didn’t change much going between the two gears. So I’m just wondering which is better for longevity.
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  3. Bean Jr.

    Bean Jr. Road Train Member

    Mar 30, 2014
    This is not specific to the ISX, but engines haven't been lasting as long as they used to. N14, series 60, and 3406 were all million mile motors. Some of the longevity is due to emissions, but a lot, IMO, is because the manufacturers recommend lugging them. I don't think 1450 is lugging an ISX, so it's up to you. Buzzing it a little would mean you're already in a more effective gear for when you need your Jake.
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  4. Judge

    Judge Road Train Member

    Mar 19, 2014
    Newport, Ar
    The ISX's sweet spot is 1,400 to 1,500 rpm at 65 mph for linehaul applications.

    1700-1900 is high end
    Won’t hurt to go to 2100.
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  5. lester

    lester Road Train Member

    Jan 2, 2012
    NW, Iowa
    I've always wondered how the can recommend such low RPM in these new engines. Maybe they are just lower torque? But I agree lugging at low rpm and high torque is a killer.
    That said 1200-1300 is about as low as I would go, and that's only if you aren't putting a full foot into it. If you are really pulling hard I'd keep it 1300+. And 1700 isn't gonna hurt a darn thing either
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  6. D.Tibbitt

    D.Tibbitt Road Train Member

    Apr 26, 2013
    Gettin' down westbound
    I always pulled with the isx at 1600 -1700 rpm and about 20psi of boost...seems to just chug up the hill, without abusing it.
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  7. seamutt

    seamutt Light Load Member

    Jun 15, 2021
    The compromise I arrived at was - for fuel economy - to try and run at lower rpm's on the flats (in low torque situations, I have a gauge), but to not be cheap and wind her up a bit going up hills. Especially so when heavily loaded. I have a new 'Endurant' automatic, and actually, 95% or more of the time, it seems to keep the rpm's about where I would, anyway. Which is convenient. But every once in a while I'll go to manual mode to keep it working constantly in a lower gear.
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  8. snowwy

    snowwy Road Train Member

    Jul 6, 2009
    Lower rpm requires more fuel and speed will drop on hills. I understand the less revolutions. But not if more throttle is required.

    Cruising the mostly flat California. I found 1500 to be better with a .5 bump in economy. I didn't lose much speed on the small ups either. But that was a 16 FL with dd15.

    1600 - 1700 is the peak range for isx 450. As mentioned above.
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  9. mitmaks

    mitmaks Road Train Member

    May 16, 2014
    I have isx15 450hp and usually cruise at 1500rpm @70mph. I do have 10spd with 3.55 gears
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  10. Brettj3876

    Brettj3876 Road Train Member

    Nov 18, 2014
    Land of local
    Since you're always heavy I say 1500-1700 for longevity. The isx 12 and 15s I've driven liked that rpm range for pulling. (2011-2015 era). Easy as hell to keep it in that range with your 18sp. And turn your fan on at the bottom of the hill, don't wait for it to heat up
  11. Brettj3876

    Brettj3876 Road Train Member

    Nov 18, 2014
    Land of local
    Back when you had mechanical engines and actually had to be a driver and not a steering wheel holder. Most trucks on the dash stated something like, operating rpm range and DO NOT LUG ENGINE written somewhere visible. Now you have color coded idiot lights
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