Op , you mean a better powerband/ more useable torque right ?
Because " hp" generally won't make your car faster. Most mods mentioned will only shift the powerband up a give you a few hp more up top but lose hp lower down. This , combined with the extra noise gives a false indication of speed :0)

If you are truly after more power , look at altering gearing or turbo/supercharging. Anything else on a euro appears to be a waste of time