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Underdrive pulley's... good or bad?

Discussion in 'The Garage' started by Topdown, Nov 12, 2003.

  1. Topdown

    Topdown 1/2 ton status

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    Underdrive pulley\'s... good or bad?

    well, I have been thinking lately that I would like to go to an underdrive pulley system in the K5... I drive it about 90% on the paved roads and rev the [darn] out of it when off-road (sand/mud) so... who knows what about underdrive pulleys? I know the benefit is more power, but whats the down side? I dont have much as far as electronics in the blazer and I dont drive much at night so I am not terribly worried about undercharging my battery... should I be? I am not terribly worried about spinning my power steering pump too slowly either... should I be?

    Someone has to know this...

    Thanks for the help!

    -Ryan
     
  2. earl87gta

    earl87gta 1/2 ton status

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    Re: Underdrive pulley\'s... good or bad?

    I have them in my TA I wouldnt put them in my truck if you ever get a winch KC lights you will notice a difrence. I would use the cash tward somthing else you will get just as much poer from buying a k&N fillter if you are looking for more performanc cheap think abought a better egnition coil ditributer intake and carb if you havet already you will be much happeir with the results unless you gust have a good deal on the pullies that is to good to pass up.
     
  3. leadfoot067

    leadfoot067 1/2 ton status

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    Re: Underdrive pulley\'s... good or bad?

    i run the moroso little crank pulley on my race car...really slows stuff down.i did it to keep the belts on at 7000+ rpms...doesnt seem to affect the cooling...although theres different schools of thought on how fast water needs to go thru a radiator to properly cool...my car never ran over 200 on the track...then when i slowed down the temp would drop about 15 degrees....as far as undercharging your battery......thats only affected at idle...how much do ya sit and idle the thing???not very often i would presume....i say go for it...the little pulleys had no negative effects on my power steering either...
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Underdrive pulley\'s... good or bad?

    Do you like your heater?

    I say leave the underdrives for dedicated vehicles that are only for fun...the charging system alone is woefully inadequate at lower RPM's even with very little load (a 37 amp stock alternator in some cases) so even something like the heater can cause issues. I know my headlights dim noticeably with the heater on high. I too would spend money on something else that isn't a tradeoff in one way or another.

    As to water pump speeds, most people have cooling problems at idle, and the slower you turn the pump, the worse cooling will be at idle. Obviously you can turn it too fast, but in general applications, I'd say underdriving the water pump is a bad idea.
     
  5. 99firehawk

    99firehawk 1/2 ton status

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    Re: Underdrive pulley\'s... good or bad?

    I have underdrive pullies on my crank and water pump on the blazer. It is daily driven, day and night. With my lights on high (all 4 lights) the heater on full (which gets very very toasty btw) the driving lights on, and my twin electric fans going at idle, the dash guage reads 13 volts
    the battery still reads 13.3-13.4.
    I do have a 1?? amp alternator off a b4c tpi camaro though.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Underdrive pulley\'s... good or bad?

    I've got an 87 amp alternator off a mid 80's Monte Carlo on mine, and with nothing on but the headlights and heater on high, the lights visibly dim. Lucky to get 13V out of the system at idle, with a brand new rebuild on it. '

    Works fine once the RPM's are up a bit, but with underdrive pulleys, it MIGHT put some of us in a really bad idle situation. Of course, I put an overdrive pulley on my alternator, and it also made no difference in output at idle.

    Just don't think the gains are worth the potential risks in most cases. Too many people already have idle cooling and idle alternator problems, underdriving those systems isn't really the right direction, but that IS my opinion, not fact, as every vehicle is going to be different.
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: Underdrive pulley\'s... good or bad?

    You know dorian, what you're saying makes perfect sense. A guy from JCI came to my work a few days ago and I was picking his brain about alternators and batteries and what it'd take to make them last longer.

    He said that 90% of today's vehicles have such a large elecrical load and not enough alternator capacity to the point that the average battery is only seeing about a 60% charge with most people taking short trips. I agree with him too from what I've seen with customer's vehicles.

    I don't think that underdriving the alternator is a good idea at all.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Underdrive pulley\'s... good or bad?

    [ QUOTE ]
    He said that 90% of today's vehicles have such a large elecrical load and not enough alternator capacity

    [/ QUOTE ]

    Why does GM need to run 140amp alternators? /forums/images/graemlins/smile.gif

    I'm sure that when I add electric fans, the already inadequate 87 amp unit will need to be replaced since I'm already seeing "problems".

    I don't really mind that I'm "only" seeing 13 volts at idle, because I spend very little time idling, but I *do* mind the dash lights and headlights visibly dimming when I come to a stop.

    Like I said though, there are a lot of variables when it comes to vehicles, and unless two vehicles are identical (which is never the case), someone will have a good experience, and others will have a bad experience. That's why it's so hard to speak in absolutes when dealing with vehicles.
     
  9. Thunder

    Thunder 3/4 ton status

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    Re: Underdrive pulley\'s... good or bad?

    Like above posts say it depends on the vehicle and how it is driven if UD pulleys will work for you. I dont know if you will see much performance boost running them in a truck.Espically if it is stock. They work best in light cars.
    If you dont already have headers, manifold, ign, exhaust, The money that UD pulleys cost would be better spent there.
    UD pulleys are basicly something you put on after you have already modified the engine to help you get the most out of it.
    I run UD pulleys on my DD 5.0 Mustang with A/C with no problems. but I have a strong batt no unusual elect loads and a good cooling system and keep idle above 750 rpm.
     
  10. 99firehawk

    99firehawk 1/2 ton status

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    Re: Underdrive pulley\'s... good or bad?

    If your lights are getting dim at idle or when you stop, you should check your battery connections, and your grounds on the fram and body and engine, even a low powered alt should do just fine at idle with factory loads on it.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Underdrive pulley\'s... good or bad?

    Actually, it's a well known fact that most older GM alternators (not sure when they changed) do NOT supply enough at idle.

    This is one of the reasons you are seeing higher amp alternators stock (it IS to put up with increased loads, but they have to compensate for idle)...a higher amp alternator still will not put out (say) 140 amps at idle, but a 140amp unit at 800RPM puts out more than a 37 amp unit at idle. Neither is capable of their rated output at idle.
     

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