Ideal cruising RPM for MP8?

Discussion in 'Experienced Truckers' Advice' started by Bdog, Feb 4, 2021.

  1. Bdog

    Bdog Road Train Member

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    Right now my MPGs average low 4s. If I regeared and got it down to say 1300 at highway speed would it make a significant difference?
     
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  3. Bdog

    Bdog Road Train Member

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    Do the make tires taller than what I have now? I don’t know. That would effectively change the ratio. The low hole gear I have honestly never used. Never needed it.
     
  4. KB3MMX

    KB3MMX Road Train Member

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    You are beating the engine up hard and are correct that 1300-1350 is ideal on that rating for cruise rpm. (1700 is out of the power band on those motors, they are happiest at 1100-1600)

    Fuel economy will definitely increase and the engine will last much longer.

    You most likely need to be in the 3.08 range. I would bet a steak dinner you pick up about 1.5 mpg or better with 3.08s ... the Mack motors hate rpm and get very thirsty up there
     
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  5. AModelCat

    AModelCat Road Train Member

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    I dunno why RPM terrifies truckers so much. Its like they think its gonna come apart if it ever hits 1800 lol.
     
  6. RockinChair

    RockinChair Road Train Member

    With 3.23 rears you could run 78MPH at 1450 RPM.
     
  7. Bdog

    Bdog Road Train Member

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    I don't think it will come apart. I have piece of heavy equipment with a CAT engine that runs at 2200 RPM all day. I just know the engines in our trucks are not optimized to be ran that high. What little reading I have done on my engine suggests that best economy and performance happens below 1,500 RPM. Torque curves and all that. It just seems if you are going to be driving 10 hours a day on the interstate with the cruise on it would be advantageous to have your engine operating in its sweet spot.
     
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  8. Moosetek13

    Moosetek13 Road Train Member

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    The sweet spot in torque is a balance between the final gear ratio and the camshaft.
     
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  9. Ridgeline

    Ridgeline Road Train Member

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    You need to change the ratio to 3.08, with the 18, you can use the lower gears without any issues at 65k
     
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  10. Brettj3876

    Brettj3876 Road Train Member

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    I know i think it's funny as hell. The schlumberger trucks were ran wide open 1900 rpm at 65 isx. The fuel mileage will suffer a bit but your not constantly pounding the #### out of it at max tq all day. Trust me that motor will last longer running higher rpms than lugging it all the time. A rebuild will cost way more than a little extra fuel
     
  11. Brettj3876

    Brettj3876 Road Train Member

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    I've driven all these newer motors except the paccar and below 1300 they all fall flat on their face
     
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