This is a common question. Here is the chart from Alta Mini Performance.



Can someone please make this a sticky for future reference.

 

That's a nice chart there. Good to see it posted here.
And this is coming from a MC owner with no supercharger.

 

But what is the Napa belt number for the stock belt?

 

I just looked online using our company NAPA Prolink,and they list the 060547 belt.And here's my story.My friend and I both had 20K miles when we both installed a 16% pulley.I used the old stock belt,he used a new one purchased at a parts store,I don't recall which one,but it wasn't NAPA.A few blasts down the street,and my car was fine! His new belt squealed above 4K RPM!Man was he mad! We put his stock belt back on,and he decided he would take the belt back to the parts store and yell at them later.However,he did drive off that night with a big grin!