If you change the VTEC crossover point with the VAFC, you absolutely must adjust fueling as well. Start with -5% HI, +5% low, once you get this right you will definitely notice a difference, I have VTEC set at 4800, and on boost she just takes off as soon as the transition occurs. It's all about the fueling. If you need more help with specifically adjusting the VAFC let me know, make small changes, if you don't have access to a dyno it' s not worth the engine damage.