I swapped the factory L99 exhaust out for a factory ZL1 NPP exhaust on my car.
Dynoed before and after a couple of hours apart. The factory L99 exhaust is not to bad, the ZL1 NPP exhaust made 4rwtq and 2rwhp at peak and 4-5rwhp through the middle over the L99 Exhaust!
It has a deeper tone at idle than the L99 and is not as raspy at wide open throttle.
Also I have 1 7/8's Stainless Power headers and no cats with both combo's.