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.
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2013 2SS/RS L99/A6 Crystal Red Metallic Tincoat 12.76@108.98mph Bone Stock
12.46@111.19mph with New Era CAI & U/D Pulley
12.12 @ 114.16 after Stainless Power headers and no tune yet on stock P-Zero's!
12.007@ 115.20 With 18" Drag Radials - 11.93 @115.19 Added a PTB 11.76 @116.59 With Yank SS3200 Converter - 11.63 @116.52 After PI and Tuning 11.44 @118.75 New Best
10.72 @127.93 after heads and Cam and Yank SS3600