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  • horsepower

    I heard that the xj makes 296 horsepower at the rear wheels is that true or no.

  • #2
    Wrong. The 4.0L H.O. puts out 190 hp stock and with driveline loss probably nets around 175 or less at the rear wheels.

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    • #3
      wouldnt it be more at the rear wheels because of gearing? i've heard the term rwhp before but i dont know if it should usually be higher or lower than engine ponies.

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      • #4
        No. RWHP is less because of driveline loss.

        At the crankshaft there is nothing draining horsepower.

        Then you attach the transmission. It takes energy to turn the transmission. That means horsepower is lost.

        Then you add a transfer case, a driveshaft, or two, and a rear axle.

        They all drain energy from the engine to do their job. Then the rear wheels themselves require energy, horsepower to move.

        So the
        Rear
        Wheel
        Horse
        Power
        is less than that at the crank.

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        • #5
          RWHP is what they call functual or actual horse power. It is not uncommon to see as much as a 25 HP loss from the crank to the tires.

          That is the beauty of syn oils like Royal Purple. You actually loose HP in your engine from it turning the crank. Like LYKOS was saying, you loose even more HP in your tranny and t-case, more is lost to your driveline(s) and in your axle(s). By adding adding a viscious oil like say Royal Purple, you are actually making it easier for your engine to turn the gears. This is how these synthetic oil producers claim that you will actually gain HP. You are making it easier for the motor to turn your gears and therefore freeing up more horse power.

          *edit*
          I was thinking about this too. HP numbers are somewhat ambigious cause if you look at the average motor, it makes the most HP in the upper RPM range. So if that 4 liter motor makes 190 horse, it probably does that at above 4,000 RPM. How often do you have your motor reved that high? If you have the auto, then you probably shift at around 2,500 to 3,000 RPM at a decent acceleration so even when you are merging onto the free way, you are probably not using all your HP. Depending on what kind of wheeling you do, what you should be concerned with is torque. Torque is the important number to most Jeepers, that is why people try to get as low as gearing as they can and still keep the Jeeps function. Since small motors dont have huge torque numbers, you compensate for that with low gears. I am rambleing now, I will shut up.
          Last edited by avainaffairs; 03-15-2006, 03:34 AM.

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          • #6
            These are the actual specs for both breeds of 4.0L

            4.0L I6 "Power Tech" - 177 hp @ 4750 rpm, 220 ft lb @ 4000 rpm - used 87-90

            4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-95 and updated in 96-01 to 225 ft lb torque @ 3000 rpm

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            • #7
              Are those the specs at the crank or the rear wheels.

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              • #8
                They are engine specs. Rear wheel specs are subjective and are followed by "rear wheel".

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