I see several aftermarket pulley kits out there.. do they help the water pump last longer? Or is just for engines that are upgraded for performance?

 

they are lighter and usually smaller except in the case of the alternator pulley i think.. this allows your crank pulley to spin more freely.. they can free up to 10 or so hp

 

There are two ways to underdrive your accessories:

1. Make the accessory's pulley larger
2. Make the main pulley smaller

The pulley kits typically to a little of both. Does it make a difference? If you are lightly modified, it's probably not worth the effort. The accessories that you are using while not work as well as they are not getting the same power (i.e. being underdriven). So if you like/need A/C, you probably don't want to use the underdrive pullies.

 

Lighter and smaller = less rotational mass

 

You don't have to go smaller to underdrive the accessories.

If you have 2 pullies, and it take one rotation of pulley #1 to turn pulley#2 one rotataion: When you make pulley #2 larger, now it doesn't complete 1 rotatation per 1 rotation of pulley #1. Thus, underdriving it.

The same works by making pulley #1 smaller (or a combination of making pulley #1 smaller and pulley #2 larger).

 

BAH power and weight difference is negligable. The only reason to get them is when eliminating the air pump, you loose alot of the belt wrap around the water pump pulley. This makes it easier for it to slip at high rpm. The Greddy pullies and other copies are larger and grooved to provide more surface area for the belt to grip.