The FrankenTurbo F4H turbocharger is no longer offered, but I had it for a while on my S4.  During that time I collected a significant amount of basic performance data on the car.  Recently I have been looking at turbocharger alternatives to the BW K04 and the metric shown below, 2-11 time, is something I have recorded for the candidate turbocharger systems.

Just to see how the F4H stacks up I pulled this data to compare the F4H to one of the top contenders, the TTE550.

The F4H uses a smaller compressor wheel and turbine wheel as compared to the TTE550, so the outcome is not surprising.

Below is the F4H under a range of ambient temperature conditions.

No surprise that as the ambient temperature increases the 2-11 time grows longer.