I would assume you're running cats? If so just take them off if you want volume, changing your mid pipe will mostly influence tone and pitch. If there is any difference in HP it's pprobably very minute like maybe 3-4 HP, depending on what size piping you use. Hope this helps.
“I don’t lose any sleep at night over the potential for failure. I cannot even spell the word.”
Gen. James "Mad Dog" Mattis USMC (Ret.)