Underdrive Pulleys
 

A New Zealand local special supplied by G^Sport, these pulleys underdrive the alternator and the water pump.

This frees up a little horse power, but the main benefit is being able to remove the air pump. You can run a short belt with the standard pulleys to remove the air pump, but the amount of contact on the water pump pulley is very marginal. The larger pulleys put less load on the belt and more surface area touching the water pump pulley.

The net effect is some dimming of lights at idle, a reduced chance of the water pump cavitating at high rpm (something the stock setup is prone to), and a slightly more responsive engine.