I have had the 5Zigen rear exhaust section for almost three weeks.
I estimate HP increase of about 3-5 HP. Driveability has improved. In other words, throttle response is better across the rev band. It accelerates better. Mid-range and top end has improved.
I do not notice bottom end loss.
The decibel level in the car has increased. At idle it sounds stock, but any amount ot throttle, especially after 3500 rpm gets noisy.
Installation was easy, about 20 minutes. If 5Zigen comes out with the remainder of the exhaust pipes from the cat-back, I'll get them. The exhaust is a quality unit, very well made.
01 IJM w/LSD & 5Zigen exhaust (soon to have springs/shocks & 5Zigen wheels).