I'm looking at replacing my stock alternator with a high output alternator for my audio in my car. And i would like to know if i will need to change the size of my belt if i switch to a high output alternator or should my stock one work.

 

I went with DC power for my alternator upgrade:

https://www.dcpowerinc.com/high-outp...3.5L+V6+VQ35DE

And your stock belt should work fine as the diameter of the alternator pulley is not changing.