If any one can help me that would be tops.

I have a VAV system and over the years extras boxes have been added on to the system with out taking into account the effects on the static pressure, flow rates etc. Which means now i am struggling to condition tenancies at the end of the duct run. I have the following fan info and am wondering how to work out the maximum speed i can drive the fan for maximum efficiency before getting cavitation etc.
Is there a program data can be input to show direct changes on motor load etc when adjusting pulley sizes?



Make : Howden
Size : 270DW Duplex
S/N : HFC 3523

Fan Motor Name plate amps : 29.5 amps
Fan motor RPM : 1460 RPM
Fan motor running current @ 50hz : 20.0 amps

Fan Motor Pulley Size : 170mm
Fan motor Shaft Size : 42mm

Fan Pulley Size : 236mm
Fan Shaft Size : 50mm

Belts : 2 x SPB-1500