alrite. I know Im stupid So what is it?

 

It's what the serpentine belt or v-belts ride on to turn the aternator, water pump and accessories.

 

Glad you asked because I didn't know it either. Thanks guys!

 

How does increasing or decreasing your pulley size of your sc make any difference with RPMs, HP, or anything of the sort?

 

Smaller pullies are easier for the engine to turn, which equals less work for the engine which equals more horsepower. Not much though.

 

with a sc, a smaller pulley will make more boost which means more hp

 

All of the pulleys are not smaller. To decrease the hp loss through the accessory drives, the driving pulley, which is the crank pulley is made smaller. This decreases the rotational speed of the whole system. In addition, the kits for stangs usually have a water pump and alternator pulley that is larger than stock. This further slows down those two accessories even more. Just remember, when the driving pulley in the system is made smaller it slows the whole system down directly proportional to the decrease in size. When the driven pulleys are made larger they decrease the rotational speed of that component.