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  • #46
    So the ATI damper is rated for 9000 rpm. I don't know how they get that number but they know what they're doing.

    The crank is supposedly made from billet 4340 steel, but i'm about 100% sure it's crappy china metallurgy. But just the change in material should have different vibration frequency right? If so, their marketed metallurgy is indeed stiffer.

    I think some of the frequency issues are created as a result of exerting lateral torque on the rotating assembly. So the damper absorbs the vibration frequency exerted by that torque??

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    • #47
      I'm reading this atm.

      http://www.atiracing.com/products/dampers/101/

      While your engine is running, some pistons are being pushed downward on a power stroke, some are being pulled down by the crankshaft, and some are being pushed upward by the crankshaft. Now envision this entire system happening 8,000+ times per minute! Even further, all of these different actions are happening to the same piece of metal - the crankshaft. These actions make the shaft twist in one direction away from its natural home location, and when it tries to come back to that home location, its momentum makes it travel past its original location and farther in the other direction.

      The measured magnitude of that action is called “Degrees of Twist – Peak to Peak” or crankshaft twist. This is what I measure when I am damper testing. It is this action that breaks parts and robs you of horsepower when there is nothing to counteract and eliminate the twist. In this system, the worst torsional vibrations, or twist, will always occur at the farthest point from the greatest load, or the heaviest mass. A torsional twist is defined as a twist without a bend. If you get too much of this twist, you will have a bend and this will cause engine and/or crank failures. Think about twisting a piece of rope over and over; you can make one or two revolutions and nothing happens. After that it starts to get a wave in it, and then as you twist more, the rope will pull your hands closer together.

      Once torsional vibrations get to the front of the engine, something there needs to counteract that motion. This is where the damper comes into play. The damper’s job is to absorb and counteract as much of the twist as possible. With the right damper on your engine, the majority of the twist can be eliminated. However, with the wrong damper, virtually all of the twist can remain. A damper’s job is to rebound like the recoil of a spring. In this case the spring is your crankshaft twisting and when it tries to rebound past that natural state we discussed earlier, that is when the damper needs to stop it.

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      • #48
        Wait.. that's bull then. If the material is different. The weights of the rods, pistons, and the crankshaft is different, then the natural frequency of the crankshaft is totally different, because the torque applied on those components is different, at which point the damper has to react to a different harmonic frequency.

        So.... I guess the best way is to get a custom damper made.

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        • #49
          TCI Auto makes The "Rattler" pendulum style of crank damper and they claim that Nascar uses them. They don't make one for Nissans, but they make one for a Pontiac 4-cylinder motor very similar in displacement to the KA motor. They require a center adapter anyway, so the technical challenge would be getting a machine shop to make an adapter to fit it to a KA motor. They claim it's effective at "any rpm". I know that's not really true, but my reading of pendulum balancers in general lead me to understand that they are more effective over a wider range, than rubber/urethane type dampers.

          That said, I see this thread has wandered away from the subject title...., ;-)
          Don Johnson (really!)
          Just so you know.

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          • #50
            http://www.bhjdynamics.com/index.php...roducts_id=132
            Don Johnson (really!)
            Just so you know.

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            • #51
              Originally posted by djsilver View Post
              TCI Auto makes The "Rattler" pendulum style of crank damper and they claim that Nascar uses them. They don't make one for Nissans, but they make one for a Pontiac 4-cylinder motor very similar in displacement to the KA motor. They require a center adapter anyway, so the technical challenge would be getting a machine shop to make an adapter to fit it to a KA motor. They claim it's effective at "any rpm". I know that's not really true, but my reading of pendulum balancers in general lead me to understand that they are more effective over a wider range, than rubber/urethane type dampers.

              That said, I see this thread has wandered away from the subject title...., ;-)
              I've noticed that. Heh.

              Sent from my SCH-I535 using Tapatalk
              '95 240sx

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