I would like to know the theory behind the underdrive pulley and why/how it gives us more power please

It's a smaller pulley so it turns the accessories slower. There by leaving the power in the motor instead of the accessories.

so what affect does this have on those accesories? Is it bad for the a/c? Bad for the alternator?

It can be I´ve heard. I have the FS PP and I have no problems what so ever with my AC or alternator. The car does accelerate a bit quicker and it revs up a lot faster than with the stock one. It´s a cheep mod, and if you´re not too heavy on the right foot like I am, you will save a few $ on gasmoney aswell.

Good luck

I guess if you sit in traffic a lot with the A/C and a powerfull sound system going full blast and the lights on your alternator might have a problem keeping up with the load.

What about the harmonic balancer thats behind the pully?

I don't see that the underdrive pulley will have any effect on the harmonic balancer. The harmonic balancer is keyed to the crankshaft and secured by a large bolt through the center.

The "under drive" crank pulley has a smaller diameter and thus pulls less belt per rev. This means all items driven by it spin slower. While this might give a tiny bit more power, it's not problem free either.

The V6 pulley is separate from the balancer. It just bolts on. The balancer or crank is otherwise not affected by this.

The pulley will not damage the water pump, AC compressor, or the alt. However it will spin them slower. This means that if you have any cooling system or electrical problems that are boarder line now they could go critical with the slower revs. AC may simply not be able to keep up with demand.

It all depends on the condition of the cooling system, AC system, how much electrical load is on the alt, what alt is in the car, and where you drive.

There is a discussion of the power pulley effect on the alternator in the Watt Story article in my cave. (electrical section.)

In general I think most people are not well served with such products. If you have to deal with allot of heavy traffic these can be a really bad idea. In traffic you could actually run the battery dead even with the car running.

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No good ever came from dark and spooky. Norville "Shaggy" Rogers

The Ogre's Fiero Cave (It's also at the top of every forum page...)

Is there such a thing as an overdrive pulley? I have one of those borderline systems and I wouldn't mind if I could spin the A/C and Alternator faster.

As far as I can see, an overdrive pulley might be bad too... you could spin your alternator way too fast at high revs and wear on the bearings. I'm not quite sure if that's the case- the ogre would know. It's probably in his cave.

Yes, there are "over drive" pulleys. Typically this is just a smaller size pulley for the alternator.

Yes, over driving is bad in many cases. You can actually blow up an alternator if you over rev it. Think same result as a skattered clutch... Can do major damage. The OE pulley is chosen partly to make sure that can't happen.

If you are low amps read Watt Story and the CS alt articles in my cave.