The Kooks X-pipe connects to the headers via a ball-and-socket-style connection, which takes some coercion to get properly seated, but seals well once in place. Once the X-pipe and mid-pipes were all bolted up, the 02 sensors were reinstalled. | 
Though the owner was loyal to his after-cat, switching to the high-quality Corsa stainless steel pipes would ensure compatibility with the Kooks X-pipe. | 
Given its reputation for quality, the Corsa Cat-Back came highly recommended from Kooks. The saucy Pace Car Edition mufflers (the loudest of two choices) have an aggressive high-pitched tone at WOT and a muscular idle, yet no low-rpm droning thanks to Corsa's Reflective Sound Cancellation Technology. The Power Pulse system uses several chambers to reflect exhaust pulses at various rpm to selectively cancel out certain tones. Additionally, the 304 stainless pipes should last the life of the car. |
The Corsa Cat-Back is bolted up one side at a time. The mufflers slip onto the hangers just behind the vented bumper, and are maneuvered until perfectly straight and even on both sides. | 
421 rear-wheel horsepower-that's a gain of 71 horses at the wheels! A not-too-shabby increase of 39 lb-ft of torque was also observed. After about five or six pulls, A&A had the air/fuel ratio pegged at 12.7:1 and the timing at 29 degrees, though with a little retard the LS1 was actually seeing 26 to 27 degrees. | 
At long last it was time to strap the C5 back to A&A's Dynojet and spin those rollers. Earlier baseline pulls had shown 350.19 hp and 353.66 lb-ft of torque (SAE). |