Yes the car is loud and not for everyday around town. It does get peoples attention though. I tried to link a quick video of my 80sc rounding turn 1 at willow springs.
It is a blast on the track and i've had no complaints on it being too loud.
I have no specific numbers on hp difference just my own feeling when i drive, and i do feel a difference.
greg.
80SC with cat & muffler bypass.