Engine Scored Underdrive Pulleys

Discussion in 'Fox 5.0 Mustang Tech' started by theYman, Jan 10, 2014.


  1. theYman

    theYman Member

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    I just scored a set of underdrive pulleys for my 93 GT from a craigslist ad for $25 including shipping. How can I find out which kit I have? They are black steel powder coated. They measure crank 4.625" water 5.25" alt 2.75". SUPPOSEDLY they are ASP Racing. I wonder if I can use the stock belt with this kit Also should I keep the stock alternator pulley 1.875" ?
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  2. mikestang63

    mikestang63 Mustang Master

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    They may be ASP, but who knows. That alt pulley seems way to big- the stock is 2 3/8 not 1 7/8. If that is what you have now, then someone swapped on an overdrive alt pulley. Running an underdrive alt pulley like the one you bought will cause all sorts of charging issues. Is your car a stick or auto? Go to the ASP or March site and they have a chart that shows you what size alt puley to use depending on your application and rpm range. You will also need to buy 4 allen head bolts and lock washers for the crank bolt if they didn't come with the pulley, as the stock ones won't work.

    For the belt, your best option is to use a piece of string and measure it that way. Then go to parts store and buy 3 belts- one that size and one 1/2" over and under . Test fit for the proper length and within the tensioner range and return the other 2.

    That being said, I would not advise using U/D pulleys unless you have a 130 amp alternator.
    #2
  3. theYman

    theYman Member

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    I am doing the alternator up grade as well.
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  4. Mustang5L5

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

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    Even with the alternator upgrade, you still need to make sure you have enough rpm of the alternator at idle to make proper voltage.

    A 2.75" pulley on the alternator is pretty large. Stick with the stock pulley, which is slightly bigger than 2". Getting a smaller 1 7/8" pulley would be even more insurance.

    Most likely,you'll need to measure for a new belt after install. If you used all 3 pulleys, you prob can use stock belt. But with that large alt pulley. You may not have enough rpm to get a charge at idle.
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  5. Grabbin' Asphalt

    Grabbin' Asphalt Mustang Master

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    I had all 3 done and it wouldn't charge well, crank,water and alt. Went back to stock alt and left the other 2 and was way better on charging. They speak truth!!!
    #5
  6. theYman

    theYman Member

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    Was this with a 130Amp 3g alternator?
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  7. Mustang5L5

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

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    Doesn't matter. The 130A alt doesn't solve all charging woes. It allows you to power things like e fan, stereo, etc safely, buy there is still a minimum rpm the alt needs to spin at to charge the battery.

    You could have a 300A alternator, but if you under drive it too much you could still have battery drain issues
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  8. theYman

    theYman Member

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    so you wouldnt recommend doing the 3G with UD pulley swap? Even if I keep the stock alt pulley? Not worth the hassle?
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  9. Grabbin' Asphalt

    Grabbin' Asphalt Mustang Master

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    Keep the stock pulley on Both:nice:
    #9
  10. mikestang63

    mikestang63 Mustang Master

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    you'll be fine with U/D pulleys as long as you have the correct combination. As I said earlier, do not use a 2 3/4" alt pulley. For a stick, I recommend that you have at least the stock alt pulley or smaller. With an AOD you must use the 1 7/8 pulley or you'll have charging problems. You may need a washer behind the pulley to achieve proper alignment and use loctite on the nut. For the H2O pulley, 5 1/4" sounds about right for most kits.

    Your cooling system needs to be in good working order as well. Example- on my current car I am running the March Power Series with the smaller 1 7/8" alt pulley. No problems whatsoever .in charging or cooling. I do have an electric fan, alum radiator, and 130 amp 3G alternator properly wired and grounded.
    Last edited: Jan 12, 2014
    #10
  11. Mustang5L5

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

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    I run U/D's, 130A alt, and an ASP 1 7/8" pulley.

    Everything runs great at idle, even with the e-fan on
    #11
  12. f8tlfiveo

    f8tlfiveo My wife likes my spool and blow-off valve.

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    I have ud pulleys on crank and water pump, no alt.. No charging issues or cooling issues. Stock alternator
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  13. theYman

    theYman Member

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    I am using the stock 2G pulley on the 3G alt . If that is too large then Ill get the 1.875 from ASP.
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  14. theYman

    theYman Member

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    Well Im finishing this up in the next day or so. I installed the stock 2G alt pulley on the 3G alternator. I used the ASP crank and water pulleys. I almost can use the stock belt but it is slightly too long. The tensioner tightens the belt but not quite enough. The indicators arrow is right at the end. I'm thinking I need a belt 1/2 to 1 inch shorter.? I was using a NAPA 25060905 90.873" and am considering a belt that is 89.47"
    #14
  15. theYman

    theYman Member

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  16. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    pick one up from your local parts store. If its not just right, you can exchange it for another
    #16
  17. theYman

    theYman Member

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    Maybe this well help someone in the future, with my under drive pulleys and the 3G Alternator with 2G pulley I was able to use the belt linked above at 90.127".

    The 3G is installed and at idle I get 14.63V at idle with all accessories on. I am having an idle surge issue now though. With nothing extra on at idle it idles perfect but as soon as I turn on the headlights or any accessory it surges from 500 to 900 rpms. If I turn the headlights off it settles back to normal idle..... turn lights on it surges.
    I have not done the extra battery ground to block yet and I am wondering if that's the cause.
    #17
  18. Grabbin' Asphalt

    Grabbin' Asphalt Mustang Master

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    You need a proper return line for the same power,lots of bad things can happen. i have 2grounds for insurance.
    #18
  19. theYman

    theYman Member

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    Yep, this was the problem. I checked resistance from the neg battery terminal to the alternator case and it was high. I added a 4 gauge ground wire from the battery and next to the existing EECC/chassis ground. I then ran a 4 gauge ground from this new point to the block. Now the resistance from the battery to any place on the motor is ZERO even at the highest setting and the car idles good again.
    #19
  20. Mustang5L5

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

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    Don't goo too crazy with grounds. One good solid ground is all you need. Putting grounds everywhere can cause ground loops.
    #20

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