1. 3.8 inches
2. normally around 7-9 psi It really does vary from car to car.
3. A lot of people tend to like it, a lot of people tend to think it's too loud. It is an aggressive sounding exhaust, maybe finding video clips of it would give you a better idea.
4. Again, this varies from car to car. Some turn a 15.5, others turn a 14.9.

hope that helps