Hi Chavvy.. no probs dood...
on a turbo car ie A3 t... then it is simply a change to the boost level and boost level cut off..
allowing a small increase in rpm can allow the boost to spiral up too. so 30 bhp is simple.. (but, the owner could do it himslef in a cruder way for 2 quid !!!! (with a brass tee piece, plumbers solder and a fine set of drills )
superchips can alter a limited amount of positions in the ecu fueling map and ignition map. These can overide the manufacturers data and richen up the mixture mid range and top given a small increase in power but hardly, if at all, noticable.
Manufacturers lean out the mixture on cruise and part throttle for both economy and emissions.. so you will lose economy slightly and emissions may increase.. all in all not really worth it on a N/a car.
Joe