I have the PE TT kit, and NISMO exhaust. When the kit was first on, I had Xerd test pipes, great pipes, fit perfect, but too loud. I took them off and put the stock cats on, now the car was quieter than stock. Stealth mode, but I wanted at least the original NISMO sound. So I got some Kinetix hiflow cats from a forum member, and took the car to my friend, a mechanic at Infinity, on Saturday we installed the high flow cats. The sound is much better but still quiet, no police problems at all driving normally, when you get on it sounds good. It does do a "gurggling" sound on deacelleration, like the test pipes, but not bad. I also had the NISMO finned differental cover installed, very nice, and since I just mounted my Kazera rims with new AVON M500 tires, had him do a 4 wheel alignment. All in all a productive day, the car sounds great. BTW, he has never driven my Z since the TT install, so he took it out back and did a massive burn out, about 20 feet, and it was loud and smokey.