Drift King Shop was offering the Supercharger (2.6) and Monkey (2.8) Rotors, which (supposedly) didn't require a dual cell mod. That said, it seems that they have been discontinued until he finds a new supplier (if he does). See this
thread.
Otherwise, it seems that the only other option is a RS Turbo (2.15) or NOS (2.35). I bought the Performance Booster kit to get the Turbo motor and the extra gears. I'd have bought the TFNTF Street Tunner kit if they'd have had it. Unfortuneately, this still isn't insanely fast. Maybe RS will come out with some faster motor(s). Perhaps in gearing up for the upcoming TFNTF sequel. Does anyone know if the new
PCB mentioned in this
thread will handle more motor than a 2.6?