Moroso 5" alternator pulley for street?

Mopar General Discussions

  1. QuickDart360

    QuickDart360 Well-Known Member

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    Hey guys! Just wonder if the 5" pulley to underdrive alternator is a good or bad idea? I found one to use. My car will have 3.91s out back. Large hydraulic mopar cam (so rpm a little high). I don't have a stereo or power drawing accessories @ the moment. Alternator is a 60 amp. I saw larger pulleys on factory hemi darts but nit sure of diameter. Please give me some insight.
     
  2. mullinax95

    mullinax95 Well-Known Member

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    I'm not sure it will be a over all benefit ... you might not gain a whole lot ... although you will gain something. I saw a 5" alternator pulley for sale the other day on here and thought "WTF".... never saw that before.
    Now to use a under drive crank pulley you will gain for sure. Got both my 408 stroker in my truck and the 360 in my cuda under drove using smaller crank pulley. :D

    Sorry I can't answer your question. Curious myself.
     
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    • QuickDart360

      QuickDart360 Well-Known Member

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      I have seen in my archive of older mopar magazines that factory hemi race cars had a larger diameter alternator pulley. So I imagine chrysler engineers had a good reason for this!! Just info on this is very vague sadly!!:(
       
    • Garry in AZ

      Garry in AZ Building a 9 second Valiant FABO Gold Member

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      The really large diameter alternator pulleys were designed for use on engines that would see continuous high RPM use, and they significantly reduce alternator output at lower engine speeds.
      In my opinion, I would not use such a large alternator pulley on a car that sees regular street duty. Maybe the handful of horsepower gained would be worthwhile for a serious track car, but there are too many disadvantages for a street car, even if you don't have a big stereo or other big loads. Your 60A alternator only makes that much current when it's spinning around 5000 rpm. (Engine RPM approx 2000) When your car is idling, or anytime you're driving slowly, the output is less. The output is also less when it gets hot.
      Now think about the current your car needs to drive on the street, and remember, anytime the car is running, the alternator is the primary source of electrical power. Here are some ballpark current values for typical systems, which your particular car may or may not have.
      1 - Ignition 5-7 amps
      2 - Fuel pump 7 -15 amps or more
      3 - Headlights 9-12 amps (low beams)
      4 - Electric radiator fan(s) 20-45 amps
      5 - Heater/AC blower fan 4-10 amps
      6 - Radio 2-4 amps
      7 - Wipers 8-12 amps
      8 - Turn signals 2 amps
      9 - Brake lights 2 amps
      10 - Other? (Stereo, additional lighting, computer, dashlight bulbs, dome lights, horn, etc)

      If you start adding things up, you can see it's not hard to use up 50 amps just driving the car normally, which only leaves 10 amps (under ideal conditions) to re-charge the battery.
      Add in a moderate car stereo amp, and a set of driving lights, and your alternator could already be too small. This is why I don't suggest a 5" alternator pulley on a street car. You'd need to keep the engine rpm's over 3500 for the majority of the time, just to keep the battery charged.
       
      Last edited: Jul 5, 2018
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      • Dana67Dart

        Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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        for street driving it is a waste of time.
        I had 3.5 dia pully and amp meter would be in the discharge at idel with breaks on. swapped out to a 2 3/4 and it is in the charge under the same conditions.
         
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