Originally Posted by Onurleft
You need test pipes, pullies, full intake and a custom dyno tune by companies like Epic MotorSports or Evolve.
There have been E9x's with these modifications reach over 390rwhp. That'll be plenty to hang with a stock C63 with all your extra weight
I dyno'd 401whp on a dyno dynamics running on 100/91 blend. My mods are listed in my sig. I haven't raced a c63 yet but I beat the previous body style E55 & E63 from a roll.