No theres no numbers on either of them. Next question, i know the really small pulleys can give belt slip issues but how would a 3.0" fair for me?

 

On a stock Magnuson pulley, the outside lip is .100 bigger than the ribs. So yes the one that measures 3.7 is a 3.6 Dia. Pulley.
Also belt slip is more of a HP issue not a pulley size issue.
I had a TVS 1900 with a 2.8 pulley with no slip.
Now I have a TVS 2300 and around 100HP more and with a 2.8 pulley it slips.

 

I would imagine that the 2300 slips with the same pulley as the 1900 because it takes more power to turn..........not because you're making more power.

 

Its kind of a combination. He's making more power because there is more boost. More boost is what in this case takes more power to spin a blower. I think the 2300 and 1900 at the same RPM and same boost are fairly comparable as far as blower drive power.

 

Blower drive power is basically [Boost*Airflow/Adiabatic Efficiency]

Bigger blower means more airflow at same rpm, spinning faster means more boost and airflow with same size blower.