hey guys if decided to start modifying my o4 xr6turbo, its envy green,leather, s/roof,premium sound, factory 18s, its a bit of a side project as my 1200 ute is getting finished off, looking at going for valve springs, 4inch exhaust in to twin 2.5's, with upgraded intercooler and piping, already have flash tuner and 60lb injectors, ready to go in, just wanting too know if you have to change the cross over section or can you leave it as is? only looking at high 200kw maybe low 300kw as I don't want the auto playing up as my wife drives the car. any advise or suggestions are greatly appreciated cheers