could be the dyno calibration, the ramp rates, air temp sensor not used
what kind of dyno is it?
i know my old 120,000km '93 GT-R made 262rwkW on two separate occasions on a DynoDynamics in shootout mode with only the following mods- Microtech LTX12 (map sensed), boost set at ~ 16psi, front pipes, 3.5" zorst, and an Exedy twinplate clutch.