I spent quite a bit of time searching for the correct belt for a Mechman alternator install.  What belt are you running on your small pulley high performance alternator?

 

THANKS!

UPDATE:
I installed the factory size belt. I'll update this after a few miles.

Factory size belt
New Tensioner and pulley
New Mechman alternator with the smaller pulley.

Isn't there an RPM limit? Curious of how fast you can run the alternator? 

I have run alternators with smaller pulleys for years on cars that rev to 7k plus. The 3250 rev limit on our trucks shouldn't be a problem.

I used the stock belt, no issues