Hey does anybody know what size supercharger pulley I should get for my 1995 SSEI, what does the pulley do?

A small pulley makes the supercharger roots spin faster, creating more boost, which results in more horsepower. That'* the basic idea, but many other factors come into play. As for what size pulley you should get, wait for one of the Series I members to chime in because I'm only familiar with Series II L67'*.

2.5", or the stock pulley from a 92/93 SSEi.

Moving to Forced Induction.