3g Alt Question

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by TOOLOW91, Sep 25, 2013.


  1. 85rkyboby

    85rkyboby Active Member

    Joined:
    Mar 3, 2011
    Messages:
    453
    Likes Received:
    57
    Trophy Points:
    39
    Location:
    South ATL
    Alright. That should do it. Any idea whether I should get the overdrive or get a smaller alt. pulley? I was thinking that the smaller alt. pulley might be better just because it'll cool the it better.
  2. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

    Joined:
    Feb 19, 2001
    Messages:
    21,365
    Likes Received:
    252
    Trophy Points:
    124
    Location:
    Massachusetts
    If you have a stock crank pulley, you should be good as it is. Going a half inch smaller on the alt pulley may not make a difference with a full size crank pulley.

    The issue really applies to those with under drive crank pulleys.

    Bit it's worth a try.

    Stock 2g alt pulley is 2", but you'll need a 5/8" ID washer as a spacer to avoid hitting the case
  3. TOOLOW91

    TOOLOW91 Mustang Master

    Joined:
    Nov 30, 1999
    Messages:
    1,948
    Likes Received:
    423
    Trophy Points:
    104
    Location:
    S.I.NY
    14 volts at idle no jumping with blinkers or anything life is good !


    Sent from my iPhone using my fingers
  4. GroverDill

    GroverDill GoldMember

    Joined:
    Aug 19, 1999
    Messages:
    4,710
    Likes Received:
    258
    Trophy Points:
    114
    Location:
    Rathdrum ID 83858
    How do you measure the pulley? My car killed its alt and it has what appears to be a tiny crank pulley ( not much larger than the balancer)

    [​IMG]

    its grande!
    Last edited: Sep 29, 2013
  5. mikestang63

    mikestang63 Mustang Master

    Joined:
    Aug 28, 2012
    Messages:
    2,744
    Likes Received:
    649
    Trophy Points:
    134
    measure them from outside diameter on one side to the other outside diameter. The stock crank pulley is 6.5"? most U/D crank pulleys are around 4.5 inches, H2O 5.5 innches, and alt 2 3/8 inches. The Powermaster or full charge kits have a smaller 1 11/16 inch alt pulley.
  6. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

    Joined:
    Feb 19, 2001
    Messages:
    21,365
    Likes Received:
    252
    Trophy Points:
    124
    Location:
    Massachusetts
    That's an Sn95 pulley. You can sort of see the ford OEM part number near the nut.

    ASP makes some good pulleys. If you have a 4" crank pulley, you can run the asp 1 7/8" alt pulley with a 5/8" ID washer as a spacer.

    http://www.summitracing.com/parts/asp-520004/applications

    As you can see, it's much smaller, so it will speed the alternator up to compensate for the crank pulley being an under drive.

    This is what I've run on my car with a 4" crank since the late 90's
    TOOLOW91 likes this.
  7. TOOLOW91

    TOOLOW91 Mustang Master

    Joined:
    Nov 30, 1999
    Messages:
    1,948
    Likes Received:
    423
    Trophy Points:
    104
    Location:
    S.I.NY
    That's what I just took off mine the smaller fox pulley makes idle a delight


    Sent from my iPhone using my fingers
  8. GroverDill

    GroverDill GoldMember

    Joined:
    Aug 19, 1999
    Messages:
    4,710
    Likes Received:
    258
    Trophy Points:
    114
    Location:
    Rathdrum ID 83858
    so using just very rough math.

    crank is 4.5"
    alt is about 2.5"

    So the alternator goes around 1.8 times per crank rotation. my car idles at 950 ish so at idle the alternator is spinning approx 1710 rpms. According to PA page alternator needs 2k rpm to make power at idle. PA also states 16k rpm alternator speed is where it will fail. Sooooo I ordered at 46mm pulley


    Thanks boys!
  9. mikestang63

    mikestang63 Mustang Master

    Joined:
    Aug 28, 2012
    Messages:
    2,744
    Likes Received:
    649
    Trophy Points:
    134
    Yep, that is why I have the 1.68 pulley. The car idles at around 750

    700 x 2.67 (4.5crank /1.68alt)= 2000 alt rpm at idle. Even if I spin my motor to 5500, I'm good. 14685@ rpm.
  10. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

    Joined:
    Feb 19, 2001
    Messages:
    21,365
    Likes Received:
    252
    Trophy Points:
    124
    Location:
    Massachusetts
    Like i said, that's been my exact setup for years. I'm using a OEM 3G alt from an SN95. Have had great idle power and no issues with upper RPMs
  11. GroverDill

    GroverDill GoldMember

    Joined:
    Aug 19, 1999
    Messages:
    4,710
    Likes Received:
    258
    Trophy Points:
    114
    Location:
    Rathdrum ID 83858
    I was just doing my research as my car seemed to be killing alternators on the dyno while being tuned, I thought it was overreving.


    plus you never drive your car :)
  12. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

    Joined:
    Feb 19, 2001
    Messages:
    21,365
    Likes Received:
    252
    Trophy Points:
    124
    Location:
    Massachusetts
    That's true now, but when i first did my 3G setup, the car was a daily driver. I learned to trust it :)
  13. GroverDill

    GroverDill GoldMember

    Joined:
    Aug 19, 1999
    Messages:
    4,710
    Likes Received:
    258
    Trophy Points:
    114
    Location:
    Rathdrum ID 83858
    To be fair the alt that just died was on my car for almost 4 years with the stock SN95 size pulley. I never really had any problems but "since I am replacing it anyhow...."
  14. Grabbin' Asphalt

    Grabbin' Asphalt Advanced Member

    Joined:
    Jun 11, 2013
    Messages:
    1,545
    Likes Received:
    206
    Trophy Points:
    74
    Location:
    Atlanta, Ga
    Here is a interesting alternator website I found, when you click on the type of pulley required it has them measured from the top grove of the pulley and not the total diameter. But they sell every type of pulley if people are searching.

    http://alternatorparts.com/alternator-pulley-size.html
  15. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

    Joined:
    Feb 19, 2001
    Messages:
    21,365
    Likes Received:
    252
    Trophy Points:
    124
    Location:
    Massachusetts
    I personally would measure where the belt rides...the top of the groove.

    That's the diameter that matters when it comes to calculating belt travel

    I'd call the pulley in Grover's post a 2.5" pulley, not 2.75"

Share This Page