Thrush,

I assure you it is bhp dependant and nothing to do with the engine spec. The absolute maximum I can get without a 5th injector is 280bhp but at this the fueling will be leaning at the top end. (As demonstrated on DanS car at recent RR shootout)

The most I can reliably get without leaning at the top end is around 240bhp.

The top end leaning is as a result of the MFI system being unable to detect any further increase in air flow at higher rpms. This is why we then add a 5th injector to take power levels up to and sometimes beyond 300bhp.