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Are there any alternators out there that will work well w/ underdrive pulle

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by PetaKane, Sep 16, 2002.

  1. PetaKane

    PetaKane 1/2 ton status

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    I've narrowed my charging problems down to the fact that I'm running underdrive pulleys. Are there any special alts out there that will work with these kinda pulleys?
     
  2. PetaKane

    PetaKane 1/2 ton status

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    Come on guys, I swear I'll never ask another alternator question /forums/images/icons/smile.gif
     
  3. heavy4x4

    heavy4x4 1/2 ton status

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    I haven't heard of any. Underdrive pulleys drive all of the engine accessories slower than normal (hence the less drag for added horsepower). So, an alternator spinning slower will not produce the power of an alternator in a stock setup.
     
  4. Supergas

    Supergas 1/2 ton status

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    I am not sure, but have you tried the Powermaster brand??? I think they are carried by Jegs... or Summit...
     
  5. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Go to any local generator shop... they should be able to sell you an under drive pully for your alt. That is what I did to counter my March pullys I put on my 454! /forums/images/icons/cool.gif

    -Dan
     
  6. RESTORE89

    RESTORE89 1/2 ton status

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    what kind of alt are you running now?
    if stock just get a higher amp unit, and it wont put out as high as rated, but it should put out higher amp than stock at same rpm's
    also think marine alternators are designed to put out higher amps at lower rpm's
     
  7. heavy4x4

    heavy4x4 1/2 ton status

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    Krazie87K5 has a point. If you could buy a smaller diameter pulley for your alternator, you'd get it to spin the alternator as fast as stock even though the belt is going slower than stock. (For those who need extra convincing that this would work, think about a bike. Pedal the same speed, but shift gears into a higher numerically gear, smaller sprocket. What happens? That's right, you go faster) Good thinking Krazie.
     
  8. RESTORE89

    RESTORE89 1/2 ton status

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    doesnt that defeat teh purpose of the underdrive pulleys?
     
  9. heavy4x4

    heavy4x4 1/2 ton status

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    I don't think so. You're changing how fast the belt spins the alternator, not how fast the belt spins. You're still driving the other accessories (waterpump, ps pump) slower than normal. Anybody else agree with me? Now I'm starting to doubt myself.
     
  10. RESTORE89

    RESTORE89 1/2 ton status

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    i guess you would still get the advantages of underdrive on the other stuff, but it would take back the power savings on the alt to turn the smaller pulley faster
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Why on earth are you running under drive? Drag racers (and others who turn high revs) run them to keep from over driving the alternator AND to free up a few HP. But, as you've found, if you don't keep revs up, things don't work. If you get an alternator that puts out like stock at lower rpms, it will be harder to turn, thus defeating the "free HP" from under driving the alternator. Nothing comes for free… In fact, you will have then wasted money on a large pulley AND a special alternator just to wind up back at square one...
     
  12. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Hehe, you beat me to it. Part of it anyway... If the whole system is under driven, then he will have the same problems on PS and other "driven" accessories.

    Bottom line, if you haven’t build a machine that constantly (or at least very frequently) sees well above stock RPMs, under driving the accessories is a waste of time and money just to buy more problems… Some street racers do successfully “under drive” slightly for a few “free HP”, but all they are really doing is taking out the slight “over build buffer” from the factory, plus they are frequently ripping around, shifting at 5-7k+ and are willing to deal with the disadvantages…
     
  13. RESTORE89

    RESTORE89 1/2 ton status

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    that was my thinking also
    dont know many street k5's that would gain from an underdrive setup. less water flow less compression on A/C less power steering pressure, and with big tires we all need as much help there as possible.
     
  14. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Exactly. With a few exceptions, most of our trucks are woefully under-geared for the tires we run, so the engine turns slow at normal street speeds. Much less what they see on the trail (unless you run a hi-po mud/sand truck). Under-drive just takes a bad situation and makes it worse...
     

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