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Internal combustion engine, front PTO

  1. Apr 10, 2016 #1
    Internal engines got a flywheel connected to the crankshaft on one side, and on the other there is a wheel that drive all the engine accessories with a belt. If the main power output would be taken from the "belt" wheel and not the flywheel, would I receive the same power output? And if no, is it possible to know which percent of the power can be achieved?
  2. jcsd
  3. Apr 10, 2016 #2


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    Assuming there is only one crankshaft in between the flywheel and the front of the motor, the engine torque should be the same at either end.
  4. Apr 10, 2016 #3


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    If only it was so easy.

    The key-way that locks the front belt pulley to the front of the crankshaft will be insufficient to transfer all the torque available from the engine. That will certainly be true for recent car engines. It is not always true for older diesel truck and tractor engines.

    The front belt pulley is often also a harmonic balancer. If you remove it, you may need to find some other way of balancing things. A motor needs a flywheel or a torque converter to keep things running smoothly. If you remove the flywheel you may have problems.

    The side force that may be applied to the front pulley is also an important consideration. The front of the crankshaft is not as well supported as the shaft in the rear main bearing, so front oil seals and bearings may be more susceptible to damage.

    If an output shaft was taken through a flexible coupling in line with the crankshaft then more torque could be carried than by using belts on a pulley. There are manufacturers tables that identifying suitable belt profiles to transfer different torque, RPM and HP.

    Remember, the sense of rotation changes when the engine is viewed from the other end.
  5. Apr 11, 2016 #4
    Pulley size and pulley material can all make a difference at the front end of the engine (racing pulleys) for example , depending on the type of transmission you have (manual or Automatic)
    At the flywheel you will have what ever the engine puts out, (rpm and HP). its the amount of this power transfer that can really make a difference at the back end. All clutches and torque converters dampen that transfer. A racing clutch for and manual, or stall torque converter for an automatic can give you more torque quicker at lower rpm.
  6. Apr 11, 2016 #5
    gjonesy, the torque at the crank on both ends of the engine will always be identical. A "racing clutch" is lighter (or sometimes simply has the mass packed into a smaller radius) than a standard clutch, so it has less inertia, so it takes less torque to accelerate it. In that sense it does change the net torque output to the drivetrain, but only when the engine is accelerating. Once the engine speed is stable the net torque is the same regardless of clutch design. I think what you are referring to as a "stall torque converter" is a high-stall torque converter. These have a higher RPM stall speed (more slip) so the engine can get to a higher RPM under acceleration conditions. Crudely stated, part of a higher torque number (at a higher engine speed) can be more than all of a lower torque number. These can be a real misery to drive on the street.
  7. Apr 11, 2016 #6
    Nothing I posted contradicts anything you just said ...lol

    Notice I said what ever the engine puts out (mostly because he never specified his HP), the only thing you can do is change how efficiently the torque is transferred.

    The only thing you can do at the front is decrease drag/resistance.....I never said he'd get more torque...lol
    What ever that crank puts out is what it puts out.

    As far as the torque converter goes I was referring to a competition kit with a low stall for lock up, A high stall basically acts like an extra gear to give you more on the top end.
  8. Apr 11, 2016 #7


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    The OP question was not about racing engine dynamics, but about how much energy could be available from the front of the crankshaft rather than the flywheel at the rear.
  9. Apr 11, 2016 #8

    Randy Beikmann

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    Baluncore's post (# 3 above) is a full, clear answer. You could theoretically take the power from either end of the crank, and get the same amount. But, the pulley-end of the crank isn't made to do it. Unless you know how to deal with the changes in stress and vibration, you're likely to have problems.
  10. Apr 12, 2016 #9
    I was simply stating that you could "maximize" the amount of power from the front with different accessories examples.....(light balanced aluminum pulleys, bypass unnecessary systems like the air-conditioning compressor ext). The correct first answer was in post 2. The crank will put out what it will put out, .. the front of the shaft spins just as fast as the back. All that being said now that I think about it, the only applications for using the front of the engine come from the crank pulley. every time you "add" something extra to the pulleys, you create more drag, and more resistance and that reduces over all performance. Unless its a supercharger..lol
  11. Apr 12, 2016 #10


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    0373.png This thread has run its course. proxy.php?image=http%3A%2F%2Fpix.iemoji.com%2Fhang33%2F0373.png

    Thanks to all.
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