[H Bomb]

i would say depends. if it is a custom tune just for your car then the tuner is gonna want to dyno it, or a good tuner anyway

if it is universal software for that X pipe then no you don't have to.

alot of people like to see what there gains are and have the car dyno bf and after though

for instance i have the Dinan Midpipe (x pipe) and Dinan Rear Muffler with there matching software and i didn't need to dyno my car. they did that already in the R&D process and so the software tune is universal for the car