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Brake Power Question

  1. Aug 4, 2008 #1

    I have the following formula: brake power = 2(pi)NT

    I also have the following figures: RPM (instant) = 3550rpm and N° of cycles over 30secs = 880.

    The engine is four stroke-one cylinder. Just wondering how do I covert the number of cycles to RPM?
    I have divided by 0.5 because it was for half a minute (30secs) but it seems I have to divide by 0.5 again is that because it is a four-stroke cycle?

    And in the brake power forumla what is the units of N if T is in Nm.

  2. jcsd
  3. Aug 5, 2008 #2


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    Gold Member

    Yes. Your engine only produces work every other stroke.

    Well that depends what your units of power are.

    Power (in Watts) is Torque (in Newton Metres) times angular speed (in radians per second).

    Since the R.H.S of the equation you quoted multiplies the speed by 2 Pi, units of speed would be revolutions per second, if power was in Watts.

  4. Aug 7, 2008 #3
    To compute :

    N = 3550 divide by 30 times 1/2 = rps unit then the unit of brake power is in watts if the torque is in Nm.

    Hope this will help...
  5. Aug 11, 2008 #4
    Correction to my post:

    N = 3550 divide by 30 = rps unit then the unit of brake power is in watts if the torque is in Nm.
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