cico

I saw a wastegate and by-pass valve kit on a brochure,i called the dealer and he told me that,fitting it, i could have gained about 28-30 cv : do you think is it possible?
And what about the reliability of the car?
My impreza is a MY 98 with a full decatted exhaust and a filter panel K&N
I wanna be sure not to break anything fitting the above mentioned kit...
Thanks guys !