general pulley question

[Fenvy]

I am looking at Genuine TRUST Greddy Pulley Kit for s13

what I dont understand is what's the difference between overdrive and underdrive pulley? which is better and why?

what kind of gain am I looking at? and how is this achieved?

[Fenvy]

bump?

[TunaFish]

An underdrive pulley is going to spin the accessory slower than normal, resulting in less load on the motor.

Powersteering would get increased effort, AC probably would not function as well, the alternator would generate less power and tend to cause lights to dim at idle.

I have never run into an overdrive pulley, but I imagine one could run one on the alternator to generate more power. However chances are it would ware out the alternator faster.

[rudee023]

BTW Greddy are neither overdrive or underdrive. They are just lighter than stock, and blue of course:D