im running just an upper... trucks been 12.83@107 on F1's and 12.76@107 on DR's i dont really have that much belt slip. as for what the smallest upper is... some trucks its a 2.80 some you can run a 2.7. smallest i could run was a 2.75 which gave me almost 2lbs of boost. it all depends on the snount and how well it was casted and machined.... the centerlines of each can be off quite a bit on some

 

What Is The Dia. Of The Sc Pulley That Comes On The 2008 Harley? What Is The Size Of The +2? Put A 3.40 On Yesterday And Saw No More Boost. Changed SC pulley, MAF and tune. Saw 372 hp at rw.

 

You're running 12.8 with just two more pounds of boost?