Do some search man, most gains comes from the hardware in the case of a downpipe, do you think all the people that has been going catless and increasing the diameter of the exhaust/downpipe are wrong??? Most people don´t have access to reprogramming their ECU´s, but the gains are still there, on the MKV our ECU´s are adaptive, the increased flow along with the lower EGT´s are taken into account by the ECU then timing advance occurs, IF you are already on stage 1 you already have a boost level that takes advantage of a downpipe and make some power out of it, even on stock tune you may find gains, stop buying all the information that comes from the dealers and do some investigation first.
On my own car i had the DP about 3 days before the Stage 2 update, i was at Stage 1 + Downpipe, the gains were there almost from the minute the DP was installed, additional 3psi on my boost gauge and great top end power, the Stage 2 tune basically removed the CEL and gave me very little gains (if any).
